MSDGC MODELING GUIDELINES AND STANDARDS VOLUME I SYSTEM WIDE MODEL

Transcription

1 MSDGC MODELING GUIDELINES AND STANDARDS VOLUME I SYSTEM WIDE MODEL REVISION 3 February 2013 Prepared for: METROPOLITAN SEWER DISTRICT OF GREATER CINCINNATI Project & Business Development Division 1600 Gest Street Cincinnati, Ohio 45204

2 EXECUTIVE SUMMARY INTRODUCTION The Metropolitan Sewer District of Greater Cincinnati (MSDGC) Volume I - System Wide Model (SWM) Modeling Guidelines and Standards is to guide modelers in model development, calibration, validation, and documentation of the System Wide Model. The intention is to provide MSDGC with accurate and consistent models of the sewer system. HISTORY OF UPDATES The initial version of the MSDGC Modeling Guidelines and Standards Volume I - System Wide Model was prepared by XCG Consultants, Inc. and developed in 2011 with the Revision 0 issued on July 29, The reviewers of Revision 0 and included: Joe Koran, P.E., MSDGC Eric Saylor, P.E., MSDGC Edward Burgess, P.E., D.WRE of CDM Philip Cheung of City of Toronto, Ontario Taymour El-Hosseiny, Ph.D., P.E. of EMH&T Philip Gray P.E., P.Eng of XCG Consultants Susan Moisio, P.E. of CH2M HILL Nancy Schultz, P.E., D.WRE of CH2M HILL Donald Wendorf, P.E. of CH2M HILL Based on the reviewers comments, an updated version of the Guidelines and Standards was issued as Revision 1 April MSDGC developed validation and calibration report templates. Revision 2 was issued in June i

3 TABLE OF CONTENTS MSDGC MODELING STANDARDS VOLUME I SYSTEM WIDE MODEL TABLE OF CONTENTS 1. INTRODUCTION Purpose of Document Audience Allowable Variance from SWM Modeling Standards (Innovation) Purpose of SWM Modeling Standards Compatible and Comparable Methods and Results Checklist for Completeness Software Discussion Software Engine Revision of SWM Modeling Standards Software Changes Innovations in Technique Document Organization MODELING OVERVIEW Uses Limitations Situations That Do Not Require Modeling Pipe Lining Addition of New Dry-Weather Flow Changes in Horizontal Layout, Manning s Value, Planned Pipe Slope Topics Outside MSDGC System Wide Model Water Quality Modeling Groundwater High Receiving Water Levels Snowmelt Modeling of Wastewater Treatment Plants MSDGC MODELING AND REVIEW PROCESS MSDGC Update Due to New Information Project Modeling Steps Step 1 - Acquire SWM from MSDGC Step 2 - Determine Project Boundaries Step 3 - Review Model Inputs Step 4 - Review Validation Data Step 5 Data Collection Plan Step 6 - Model Validation Step 7 - Model Calibration Step 8 - Documentation Step 9 - MSDGC Review Step 10 - Model Alternatives, Evaluation, and Recommendations Step 11 - New Information Following MSDGC Review of Base Model STANDARDS FOR DETERMINING IF CHANGES TO THE MODEL ARE NECESSARY Existing Conditions Version of the System Wide Model Increased Detail and Model Updates for Project Area ii

4 TABLE OF CONTENTS 5. GENERAL MODELING METHODOLOGY Standards for General Modeling Methodology Data Quality Review Flow Data Rain Data Radar Rainfall Thiessen Polygon Method Single Rain Gauge or Design Storm GIS Field Verification Survey vs. Measurement Coordination with MSDGC General Model Options Infiltration Method Ponding at Nodes Dynamic Model Routing Time Frame of Model Run - Dates Time Period Before Recording Results Start of Analysis Time Period Before Rainfall Start of Reporting Time Period Following Rainfall End of Analysis Time Step for Model Run Reporting Time Step Runoff Time Step Routing Time Step Boundary Condition and Hot Start Files MSDGC Modeling Units Evaporation Evaporation from Literature Evaporation from Calculation Hydrology EPA-SWMM Surface Runoff Methodology Subcatchments Allowable Changes to Hydrologic Parameters Width Slope Percent Impervious Hydraulically Connected Impervious Area GIS Calculation Literature Value Surface Roughness Using Manning s n Depression Storage Infiltration Method Hydraulic Network Nodes Junctions Outfalls Dividers Storage Units Inflows to Nodes Subcatchment Runoff Dry Weather Flow Estimation from Observed Data iii

5 TABLE OF CONTENTS Estimation from Water Supply Data Estimation from Similar Land Use Estimation from Literature Values Diurnal and Seasonal Patterns RDII Methodology Links Conduits Straight Line Alignment Significant Bends Drop manhole Pumps Orifices Weirs Outlets MODELING TECHNIQUES FOR SPECIFIC SITUATIONS Standards for Modeling Specific Situations Naming Conventions Review Impacts Upstream Backwater Impacts Pipe Capacity & Flooding Manholes Downstream CSO Volumes High Rate Treatment Systems Level of Detail in Modeling Storage HRT Pumping Sludge Return to Interceptor Possible Variations Control Rules Condition Clause Action Clause Priority Value Control Curves Control Rule Examples Real Time Control Full Real Time Control Direct Real Time Control Proportional Integral Derivatives Pumps and Force Mains Pump Force Main Flap Gates Storage Tanks Tunnels Regulators and CSO Structures Single Chamber Regulator Dual Chamber Regulator Control Curve Non-Circular Sewers Pipe Shapes Custom Link iv

6 TABLE OF CONTENTS 6.12 Lining of Sewers Low Impact Development Modeling Parameters Porosity and Storage Volume Infiltration Parameters LID Controls Modeling LID Control Editor LID Within Subcatchments LID as Subcatchments Sewer Separation GUIDELINES FOR VALIDATION OF UPDATED MODEL Validation Storms Expected Accuracy Dry Weather Flow Peak Flow Total Flow Volume Flow Hydrograph Shape Velocity Depth of Water Validation Results Compliance Non-Compliance CALIBRATION METHODOLOGY WaPUG Code of Practice for the Hydraulic Modeling of Sewer Systems Dry Weather Flow Peak Flow Total Flow Volume Flow Hydrograph Shape Velocity Depth of Water Selection of Calibration and Validation Storms Antecedent Conditions Duration of Storms vs. Time of Concentration Continuous Period vs. Storm Duration Limitations to EPA-SWMM Calibration Moving Sediment Debris Inflatable Dam Weir Coefficients Calibration Discussion Incremental Sub-basins Timing of the Rising Limb Surface Runoff Subcatchments and RDII Areas Output checks Continuity Error Review Rainfall Hydrology Hydraulics Node Flooding Standard Tables, Plots, and Summary Discussion Requirements v

7 TABLE OF CONTENTS 9. GUIDELINES FOR DOCUMENTING CHANGES TO THE MODEL Reports by Modeling Phase Model Review Report Model Changes Report Model Validation Report Model Calibration Report Model Review Documentation Modeling Project and Project Area Description Boundaries of Modeling Project Boundary Conditions Files Used For the Final Model Boundary Conditions Files Provided by Others Boundary Conditions Files Used by Modeler to Speed Development Projects Outside the Project Area Developed by Others Description of SWM provided by MSDGC Model Parameters Outside of Expected Values Proposed Changes to Model Parameters Based on Review Description of Available Data Data Collection Plan Model Changes Documentation Description of Data Sources Used References and Methods for Determining Parameters General Description of Changes Appendix Containing all Parameters Changed Model Validation and Calibration Reports Description of the Flow and Rain Data Sources Used Justification of the Storms Used Recurrence Interval and Other Descriptions of Storms Used Justification of the Flow Data Used Available Data Quality Challenges in Validation and Calibration Tables and Graphs Comparing Observed and Modeled Flows and Levels Overall Discussion of the Results Justification of Accepting Model as Validated Resulting Course of Action Project-based Actions SWM Actions Impacts of Changes Conclusion References APPENDIX A APPENDIX B SYSTEM WIDE MODEL WORK PLANS STANDARD FORMS AND REPORTS LIST OF TABLES Table 5-1 Table of General Modeling Methodology Standards Table 5-1 Standard Units Table 5-2 Monthly Pan Evaporation for Hamilton County, OH Table 5-3 Percent Impervious by Land Use vi

8 TABLE OF CONTENTS Table 5-4 Manning's Roughness n for Overland Flow Table 5-5 Typical Depression Storage Values Table 5-6 Infiltration Parameters Table 5-7 Soil Characteristics Table 6-1 Table of Standards for Modeling Specific Situations Table 6-1 Control Rule Attributes Table 6-2 Soil Classification and Porosity Table 6-3 LID Control Layers Table 6-4 LID Surface Layer Parameters Table 6-5 Characteristics of Various Soils Table 6-6 HCO by Soil Type Table 9-1 Example Flow Monitor Location, Contributing Inflow Pipe and Acreage9-9 Table 9-2 Example Wet Weather Events Table 9-3 Example Recurrence Intervals Table Table 9-4 Example Peak Flows and Volumes for a Wet Weather Event Table 9-5 Example Visual Checks for Peak Timing and Hydrograph Shape LIST OF FIGURES Figure 3-1 Project Modeling Steps Figure 4-1 Flow Chart for Achieving Validation Figure 5-1 Thiessen Polygon for Rain Gages Figure 5-2 Losses at Bends Figure 6-1 Typical HRT Set-up Figure 6-2 Typical Starting Parameters for PID Values Figure 6-3 Variability Around Set Point based on Proportionality Factor, K Figure 6-4 Variability Around Set Point based on Derivation Time, TD Figure 6-5 Variability Around Set Point based on Integration Time, TI Figure 6-6 Pump Modeling Figure 6-7 Schematic of Single Chamber Regulator Figure 6-8 Schematic of Dual Chamber Regulator Figure 6-9 EPA SWMM Standard Pipe Shapes Figure 6-10 EPA-SWMM Pipe Shape Comparison Figure 7-1 Example Plot showing Observed vs. Modeled Flow data and the Acceptable Error Bands Figure 8-1 Flow Meter Locations Figure 9-1 Example of Rain Gauge Network and Flow Monitoring Locations Figure 9-2 Example Observed vs. Modeled Flow Data and Acceptable Error Bands9-14 Figure 9-3 Example Calibration or Validation Plot with Smoothed Observed Data9-14 vii

9 TABLE OF CONTENTS Acronyms and Definitions CAGIS Cincinnati Area Geographic Information System Calibration Adjustment of model parameters to better match observed data CAPP Capacity Assurance Program Plan sanitary sewer system upgrade plan CSO Combined Sewer Overflow flow from combined sewer in excess of interceptor capacity that is discharged to an open channel or stream DUC Dynamic Underflow Control System of sensors and gates to automatically maximize flow to the interceptor and minimize overflows DWF Dry Weather Flow low flow of sanitary discharge and base groundwater infiltration without stormwater or rainfall derived inflow and infiltration EHRT Enhanced High Rate Treatment Chemically-based enhanced sewage treatment system for treating wet weather flows before discharge to receiving stream GIS Geographic Information System (includes generic mapping and CAGIS) HRT High Rate Treatment Primary sewage treatment system for treating wet weather flows before discharge to receiving stream LID Low Impact Development structures and techniques for reducing water quantity and water quality impacts of development compared to standard construction LTCP Long Term Control Plan combined sewer system upgrade plan MSDGC Metropolitan Sewer District of Greater Cincinnati PBD MSDGC division for Planning and Business Development RDII Rainfall Derived Inflow and Infiltration rainwater directly or indirectly flowing into a sewer RTC Real Time Control System of gates, moveable dams, and sensors that automatically operates to maximize storage in combined sewers, maximize volume of flow to interceptor, and minimize overflows RTK RDII modeling method using R as fraction of rain entering sewer, T as time to peak inflow and K as duration of recession limb to time to peak SSES Sewer System Evaluation Studies The inventory and inspection of a sanitary sewer system which may include manhole inspections, smoke/dye testing, and closed circuit television inspections (CCTV) SSO Sanitary Sewer Overflow flow from sanitary sewer in excess of interceptor capacity that is discharged to an open channel or stream SWM System Wide Model model input file of sewer system Validation Comparison of model results to observed data without adjustment of model parameters WaPUG Wastewater Users Group group of experts that developed standards on expected model accuracy viii

10 TABLE OF CONTENTS WWIP Wet Weather Improvement Plan merged plan for upgrading both sanitary and combined sewers WWTP Wastewater Treatment Plant ix

11 INTRODUCTION 1. INTRODUCTION In 2003 the Metropolitan Sewer District of Greater Cincinnati (MSDGC) developed seven hydraulic models of a portion of its collection system to study, plan, and design solutions. Each sewershed has its own distinct hydrologic and hydraulic model. For the purposes of this document, System Wide Model (SWM) encompasses each of the seven distinct collection system models. The SWM includes all combined pipes 18 inches in diameter and larger, and all sanitary pipes 12 inches in diameter and larger. The SWM is intended for modeling hydrology and hydraulics in the sewer system. Other uses such as water quality modeling are outside the current scope of the SWM and are not discussed in this document. The current SWM uses the U.S. Environmental Protection Agency (EPA) SWMM engine. This document will be adjusted if MSDGC decides to use different modeling software in the future. The SWM gives MSDGC a tool to evaluate for both existing and future conditions, as well as to analyze proposed improvement projects before construction. The SWM was further developed to include proposed solutions models supporting the Wet Weather Improvement Plan (WWIP), the Capacity Assurance Program Plan (CAPP), the Long Term Control Plan Update (LTCP Update), and other studies. For the CAPP released in 2006, MSDGC used standards developed by CDM as documented in the CAPP Modeling Standards dated January These standards and protocols were further developed by a team of experts as documented in the Wet Weather Improvement Program Volume IV: Protocols and White Papers, June MSDGC regards this as a dynamic document, with continual updates and reviews occurring as needed. Just as the MSDGC collection system changes over time, the SWM and the methodology for that SWM will also change and be updated as needed. 1.1 Purpose of Document As land development and redevelopment, and sewer system repairs, replacement, and improvements continue throughout Hamilton County, MSDGC needs to standardize methods as much as possible and to allow innovation where needed. MSDGC views the modeler as owning the particular version of the model developed for a project. This Guideline & Standards document is intended to guide the modeler through the development and documentation of the model for a project. The modeler s documentation forms a justification of the changes to the model. This document is intended to: 1. Provide technical support and guidance to those involved with developing, using, reviewing, or any other aspect or activity related to hydrologic, hydraulic, and water quality modeling for MSDGC 2. Ensure consistency in modeling and reporting on the MSDGC collection systems. 3. Produce accurate and reliable models that represent MSDGC s collection system. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 1-1

12 INTRODUCTION Audience The primary audience for this document is those who are directly responsible for developing, updating, using, and reviewing the hydrologic and hydraulic computer modeling of the MSDGC collection system. While some of the information will be of interest to planners and other non-modelers, this document assumes some familiarity with modeling and the modeling software Allowable Variance from SWM Modeling Standards (Innovation) The modeling techniques described in this document have been successfully used to model MSDGC sewer systems. Although specific model approaches are described in herein, alternative approaches are not excluded. Additional data, changing conditions, updated software, etc. may allow new methods. MSDGC recognizes that innovation will occur and intends this document to provide a framework for the documentation, review, and acceptance of alternative methods. However, it should be noted that at any time during the project, deviation from these standards requires written approval from the Principal or Supervising Engineer of the Planning and Business Development (PBD) Modeling and Monitoring Group. 1.2 Purpose of SWM Modeling Standards The objective of the MSDGC SWM Modeling Standards is to provide a consistent approach to modeling, documentation, review and acceptance. The following section describes elements considered in establishing modeling standards Compatible and Comparable Methods and Results The SWM Modeling Standards are intended to provide MSDGC with a consistent approach to the development, validation/calibration, application, and interpretation of models regardless of the individuals and organizations performing the modeling. This document presents decisions already made (i.e., acceptable range of Manning s roughness coefficient (n), methods of modeling the separation of combined sewers, etc.) in other situations so the modeler can focus on new or unique situations Checklist for Completeness Sections regarding review and documentation can be viewed as a checklist for use by the modelers and reviewers during a project. Modelers are expected to use this Guideline & Standards document to review their own efforts and to produce the documentation required by the reviewers. Additionally, this document describes the expectations of the model reviewers so the modelers can fully document their efforts and speed the review process. 1.3 Software Discussion MSDGC has invested significantly in the development of the SWM. The SWM has played an important role in the hydrologic and hydraulic model used extensively in the development of the 2006 WWIP and by MSDGC staff and the consulting community in the planning, evaluation, and design of many projects in the District. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 1-2

13 INTRODUCTION The SWM was originally developed in EPA SWMM4 and migrated to EPA SWMM5 in The model has been updated as projects or assignments have moved forward. MSDGC has been using EPA-SWMM software for system planning analysis as well as project-specific needs Software Engine EPA-SWMM is the current modeling software used by MSDGC. EPA-SWMM is a single-user software package and has no direct cost associated with it. MSDGC has selected EPA-SWMM as the software to be used in developing future hydrologic and hydraulic models. This document assumes the use of this version of the EPA-SWMM software. The EPA-SWMM modeling software package has several benefits including: Federally approved modeling software Free download Not proprietary, and easily ported to other hydraulic software packages Used to develop MSDGC s SWM Online users group available to discuss software and modeling issues While EPA-SWMM is a capable software package for a majority of MSDGC s modeling needs, it does have limitations with respect to data management, review, and scenario management. Challenges include: No scenario manager, as each input file is a single time period and set of input parameters Limited results review including fixed output tables Limited data management, such as formats for input data No Geographic Information System (GIS) interaction Limited user interface All modeling work performed must be provided to MSDGC in the format of the MSDGC standard software. Calibration runs and final alternative scenarios must be run in the standard software, with the input and output files provided to MSDGC. Submissions for review include the model input files as well as any supporting files, such as boundary conditions time series, rainfall time series, and any supporting external files. All documentation reporting and supporting changes to the model and describing calibration efforts should be included. 1.4 Revision of SWM Modeling Standards As stated before, this SWM Modeling Standards is a living document and will be updated and changed as needed. Several different changes may come about in the future that will require an update of techniques or the addition of different sections as new or updated features become available. Proposed changes to the SWM Modeling Standards should be submitted to the Principal or Supervising Engineer of the PBD Modeling and Monitoring Group for review and possible inclusion in future versions of the SWM Modeling Guidelines and Standards. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 1-3

14 INTRODUCTION The following sections highlight only a few reasons for an update/revision of this document Software Changes The standard modeling software for MSDGC at this time is EPA SWMM The developers of EPA SWMM are constantly updating and making revisions to the modeling software. In the future, EPA SWMM may offer different features that ease working with Low Impact Development (LID) strategies and Real Time Control (RTC) facilities. In the future, MSDGC may want to move to a different modeling package. In either case, this document will need to adapt to future decisions made by MSDGC Innovations in Technique The modeling techniques described herein have been used to best represent the physical reality within the limitations of the software and the available data. Improved (more accurate, more fully representative) techniques are expected to be developed through the experiences of various modelers, the availability of more information, and on-going development of software tools. 1.5 Document Organization The remainder of this document is organized as follows: Section 2 provides an overview of general modeling Section 3 describes MSDGC modeling and review process to ensure consistency Section 4 provides guidance to the modeler on determining when the existing model needs to be updated Section 5 lists general modeling guidelines for MSDGC sewer systems Section 6 offers guidance on modeling specific situations that may be encountered Section 7 provides validating the existing model as sufficiently calibrated without further changes Section 8 describes guidelines for calibrating an updated model Section 9 presents documentation requirements for describing model validation and calibration, and model changes MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 1-4

15 MODELING OVERVIEW 2.1 Uses 2. MODELING OVERVIEW A hydrologic and hydraulic model is a computer-generated simulation of flow into and through a sewer and channel network. A sewer system model allows users to view flows, levels, velocities, and surcharge conditions in many areas of the sewer network at the same time. Blending fixed information (pipe diameter, manhole elevation, etc.) with variable information (rainfall, flow, water level, etc.), a model will estimate the conditions throughout the sewer system. The computerized model is a valuable tool for assessing current conditions and for the planning, evaluation, and design of projects within a system. Models allow the user to simulate proposed system improvements before construction, and to develop and evaluate different scenarios. Models also allow future conditions to be simulated to help determine the impact of changes. In the development of computer models, the objectives must be defined early in the process. The objectives will help define the importance of modeling assumptions (i.e., Dry Weather Flow [DWF] pattern vs. average value) and the level of detail in the model (i.e., 18-inch-diameter pipe only, or down to the 6-inch-diameter pipe). 2.2 Limitations One limitation of computer modeling is the quality of data used in the model development, update, and calibration. Often there is not sufficient data available for model development and calibration for specific areas. For example, as-built records of an older collection system may be difficult to acquire. Calibration data (rainfall, flows, etc.) may be limited in location, time, and quality of data. The primary limitation in flow monitoring for calibration data is the possible inaccuracy in the flow measurement. This inaccuracy can be ±10% error or more, resulting from errors in the level measurement, the velocity measurement, and the pipe cross section measurements. These three measurements are used in each instantaneous calculation of flow, so small errors (on the order of 2%) in each measurement combine to become a larger error. Turbulence and debris movement during high flows can exacerbate errors in flow monitoring. The 10% error can be expected during normal flow conditions and can be greater during higher flow conditions. In building and calibrating the model, parameter selection and estimation is usually determined by the modeler. Tables of typical value ranges are available for parameters such as Manning s roughness, soil characteristics, etc., but it is up to the modeler to make an engineering decision concerning the application of these values. For many of the parameters, the model software or the observed data support the selection of a single value for a parameter that varies in the physical reality. For example, the roughness of a grass surface varies throughout the year: low in the winter (lack of growth), high in the spring and fall (growth triggered by warm temperatures and adequate rainfall), and low in the summer (drought). MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 2-1

16 MODELING OVERVIEW The end-user of the model should understand the uncertainty and sensitivity of the assumptions made in model development. Therefore, modelers must quantify and present the uncertainty of their model output. This information allows end-users the opportunity to evaluate the results and the confidence that should be placed in them. Another concern with computer modeling is not with the structure or processes of the model itself, but in how the model output is interpreted. This issue can be minimized by clearly defining the design problems to be addressed by the modeling exercise to end with a thorough interpretation of the model results, their uncertainty, and their relationship to the design questions. 2.3 Situations That Do Not Require Modeling Pipe Lining Model requests for pipe lining typically fall into two categories: a. Does the current pipe have capacity? b. How will lining affect the capacity of the pipe? Modeling requests that fall under the first category should be performed to evaluate the current capacity of the pipe and determine if lining is the appropriate solution to the problem. If the pipe is modeled as under capacity, additional investigation may be warranted. Modeling requests that fall under the second category do not need to be performed. Typically, liners range in size from 6-mm thick for an 8-inch pipe to 27-mm thick for a 30-inch pipe. This translates to a loss of 6-7% of pipe diameter, which is well within all of the other sources of potential error in the model Addition of new Dry-weather flow Generally, unless it is a large area, the addition of dry-weather flow to the model does not have a great impact. Adding new dry-weather flow area most likely does not require a full-scale modeling effort. Currently, model results are reported in cubic feet per second (cfs) to one decimal place. If the additional dry-weather flow is less than 0.1 cfs, the impact will not be shown in the reported model results. If the additional dry-weather flow is greater than or equal to 0.1 cfs, modeling is still not required if it is adding less than 10% to the existing dry-weather flow Changes in Horizontal Layout, Manning s value, Planned Pipe Slope Changes to horizontal layout do not generally need to be re-modeled if the change does not increase the pipe length or change the pipe slope. Even if the pipe length or pipe slope is changed, modeling may still not be required, if the designer calculates that changes in pipe slope or length will not change the design flow of the pipe by more than 10% MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 2-2

17 MODELING OVERVIEW 2.4 Topics Outside MSDGC System Wide Model For this Guidelines & Standards document, the topics outlined below are considered outside the MSDGC SWM effort. The level of effort involved in developing and adding the required model data are greater than the presumed level of accuracy and the impact on the model results would justify Water Quality Modeling At this time, MSDGC generally does not use EPA-SWMM for modeling water quality. Flow hydrographs from EPA-SWMM have been used by MSDGC as inputs for separate water quality models. Water quality modeling is discussed in Volume 3 of the MSDGC Modeling Guideline & Standards Groundwater MSDGC does not generally model the groundwater flows in its system. Given the volume of data needed to model groundwater impacts on the sewer networks and the presumed accuracy of the model results, the value of the model impacts is considered minimal. The inflow into the system from groundwater is modeled using other methods such as RTK into separate sewer systems or adjusting the runoff parameters for combined sewer systems High Receiving Water Levels The SWM generally does not consider receiving stream water levels. For major streams such as the Ohio River, Little Miami River, and Mill Creek, the scale of the effort in developing models is beyond the current scope. Specific smaller streams, such as Duck Creek and West Fork, have been added where the receiving stream water levels have a direct impact on combined sewer overflow (CSO) performance, water level data are available, and the modeling effort is manageable. Surface water intrusion is a problem in the MSDGC network. Sometimes the Ohio River, Mill Creek, etc. will rise and enter the MSDGC system either through infiltration by raising groundwater levels or by direct inflow through an open CSO flap gate, damaged manhole, etc. Estimation of this inflow is difficult. One way to manage the effects of direct inflow to the MSDGC system is to set a boundary condition on all CSO overflows equal to the river stage of the receiving stream. Unfortunately, this analysis can only be done for observed storms with reliable river stage data or for design storms. Water level data (usually 15-minute interval) is available through the United States Geological Survey (USGS) website for limited locations in the MSDGC service area. The impact of high water on sewer flows can only be accurately reproduced with flow monitoring and receiving water level monitoring. From these data, relationships may be determined linking the water level to the resulting flows in the sewers. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 2-3

18 MODELING OVERVIEW Through frequency analysis of the local storms and the levels in the receiving waters, an assumed receiving water level can be determined for a project. These water levels are normally determined specifically for a project Snowmelt Snowmelt is a form of runoff not commonly accounted for in the SWM. Although the model has the capability to simulate snowmelt, this analysis is only possible when coupled with a tremendous amount of reliable data. Some of the parameters required are real-time temperature, temperature at which snowmelt occurs, and many other snow pack parameters. Snow can only be incorporated into the model as it as an equivalent depth in rain. For calibration of the model, the observed snowfall is only possible through the use of heated rain gauges. Currently, MSDGC does not have any heated rain gauges in its network and has decided not to install them. In addition, the climate for the greater Cincinnati area limits the need to model snowmelt. Typically, snowmelt in this region does not significantly impact the performance of the collection system because limited depth of accumulated snow leads to limited volumes of runoff during snowmelt. Therefore, the climate does not justify the time and expense required to gather the data necessary to include snowmelt in the model Modeling of Wastewater Treatment Plants MSDGC staff is currently in the process of developing hydraulic models for each of the seven major wastewater treatment plants (WWTPs). The modeling of the WWTPs is discussed in Volume 2 of the MSDGC Modeling Guidelines & Standards. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 2-4

19 MSDGC REVIEW 3. MSDGC MODELING AND REVIEW PROCESS This section describes the steps that modelers will follow when the SWM is required for project modeling and model updates. This section is intended to guide the modelers through the model development and review phases. 3.1 MSDGC Update Due to New Information As MSDGC continuously improves the collection system, the SWM needs to reflect the system or condition changes. Sources of new data include construction of new or replacement structures, changes to pump ratings or operating rules, discovery of construction drawings, as well as surveys and inspections. Periodically MSDGC will update the model parameters based on updated information. The updated model may not be adjusted to improve calibration following the update. The modeler is responsible for the validation and documentation of the model status before project development. The update of the model based on new information and an overall re-calibration of any of the seven collection system models will follow the work plans developed by MSDGC for each model. 3.2 Project Modeling Steps MSDGC believes the modelers for a project need ownership of the model used for the project. The depth of review, the type and detail of data collected for model update, the adjustment of parameters, the level of validation or calibration, and the techniques used for modeling are the responsibility of the modelers. In the proposal stage of the project development, the modeler will propose the level of detail to be used in following the SWM Modeling Guidelines & Standards, including boundaries of model review and possible deviations from the SWM Modeling Standards. For example, small projects may not require the same level of review as WWIP bundle projects. The modelers must defend and thoroughly document in EPA-SWMM any changes to the SWM for MSDGC s review as part of the review process. The steps for project modeling are shown in Figure 3-1. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 3-1

20 MSDGC REVIEW Figure 3-1 Project Modeling Steps Project Modeling Steps Step 1 Aquire SWM from MSDGC Step 2 Determine Project Boundaries Step 5 Data Collection Plan Step 4 Review & Document Validation Data Step 3 Review & Document Model Inputs Step 6 Model Validation Step 7 Model Calibration Step 8 Documentation Step 11 New Information Following MSDGC Review of Base Model Step 10 Model Alternatives, Evaluation, and Recommendations Step 9 MSDGC Review Step 1 - Acquire SWM from MSDGC Project modeling should begin by acquiring the most recent SWM for the project from the MSDGC PBD Modeling and Monitoring Group. The modelers must review all aspects of the model with MSDGC to identify possible limitations of the current model (level of calibration, certainty of pump curves and WWTP operation, etc.) for the specific project needs. In addition, the needs of MSDGC for updating the model will be discussed as well as the status of the model work plan. Appendix A includes the MSDGC work plan for each SWM. Documentation of previous modeling projects that changed the model parameters will be available from PBD Modeling and Monitoring Group for modelers of current projects. The modeling software to be used for each project should be verified with MSDGC to maintain consistency between model input files. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 3-2

21 MSDGC REVIEW An important topic of discussion with MSDGC will be the status of other projects in the same sewershed as the project. Current and possible future projects may impact flows into the project area, change the downstream conditions (flow and/or water levels), alter the timing of flows, and/or change the WWTP operations. The combined impact of all projects must be considered for Sanitary Sewer Overflow (SSO) and CSO volumes, pump station and conveyance capacity, WWTP capacity, etc. Proper modeling of the other projects will likely involve coordination within the MSDGC organization and with other consulting groups Step 2 - Determine Project Boundaries Once the specific SWM has been obtained, the modeler shall perform the following tasks: 1. Delineate and confirm the specific area of interest within the sewershed model. Identify SSOs and CSOs that may be affected by system hydrology or hydraulics modification. 2. Establish suitable boundary conditions for assessments. Define boundary conditions (head and flow) sufficiently to recognize upstream and downstream influences. Be aware that other projects may impact the boundary conditions. 3. Identify where additional catchment delineation detail or collection system information is required to meet the modeling objectives of the project. In general, the SWM combined sewer system model includes pipes as small as 18 inches in diameter and separate sanitary areas as small as 12 inches in diameter. Additional detail may be required depending on the specific project and the availability of information Step 3 - Review Model Inputs The modeler will perform a preliminary review of model hydrology and hydraulics with data needs assessed and identified. Model attribute information should be reviewed in GIS and any discrepancies resolved through data requests to MSDGC and field visits. Model input parameters will be reviewed to ensure that values fall within expected range corresponding to the physical condition. Input parameters will also be analyzed for possible anomalies and flagged for further investigation Step 4 - Review Validation Data The modeler should work with MSDGC to identify available flow monitoring and rainfall data and to review GIS data. If flow monitoring data are not available or are insufficient, the modeler should identify the need for flow monitoring and potential locations, and provide this recommendation to MSDGC. Insufficient data may include flows collected during: 1. Unusually wet or dry periods with abnormal rainfall-to-runoff characteristics. 2. Periods with only small storms (if calibrated only to small storms, the model may poorly simulate larger storms). MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 3-3

22 MSDGC REVIEW 3. Periods before major system changes (major change in land use, sewer separation, RTC, etc.) such that the flows do not correspond to the modeled collection system. 4. Periods of data with large or frequent gaps (poor data quality), so peak flows or water levels are missed or volume calculations may not be complete. The modeler will review available flow and rain data for completeness and utility for model validation and calibration. The modeler will prepare a data summary to document the available flow and rain data, discuss any data shortcomings, and identify additional data needs. MSDGC has procedures in place for the initial review of rain and flow monitoring data. Because of the volume of data regularly collected by MSDGC, this review will never be as comprehensive as a review by modelers investigating a specific area and period of time. The modeler is expected to review the available data to identify periods of data for use in modeling. For flow and level data, the data review should include: Conservation of volume through downstream monitors; Extreme changes in depth, velocity, and/or flow; Extreme values of depth, velocity and/or flow; Depth or velocity measurements outside range of instrument; Scatter plots of depth to velocity and depth to flow for consistency; Periods of supercritical flow and hydraulic jumps; Periods of receiving water intrusion Step 5 Data Collection Plan Based on the review of the SWM, discussions with MSDGC and others about the project area and about other projects in the system, and the monitoring data review, the modeler will develop a Data Collection Plan. Data Collection Plans include the following tasks: Acquire construction drawings Review reports related to the project area and the sewer system Site visits Meetings or other communication with MSDGC personnel Detailed review of flow monitoring Schedule of activities After review and acceptance by MSDGC, the Data Collection Plan will be implemented. This step may continue for some time and may coincide with other aspects of the project. For example, flow monitoring may coincide with the initial calibration of the model using existing flow data Step 6 - Model Validation Model validation occurs if the model inputs have not been significantly changed, or once the calibration process has taken place. The objective of validation is to document that the model is a reasonable representation of the system. Model MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 3-4

23 MSDGC REVIEW validation will use observed data to verify that the model represents the MSDGC system. Data used in the validation process includes flow and level monitoring, overflow activations, WWTP records, reported manhole flooding and basement backups, and discussions with field personnel. The validation results should be compared with the calibration requirements discussed in later sections (Sections 7, 8, and 9). If the model is validated as adequately representing the current conditions, the results are documented according to later sections of this document (Sections 7, 8, and 9) and submitted to MSDGC for review and approval. This documentation will specifically discuss whether further data collection and calibration are needed. A model validation report template is included in Appendix B Step 7 - Model Calibration Calibration of the hydraulic model must be completed if the model data have been revised, or if the model was not validated upon initial simulations. Acceptable errors from observed data are discussed in later sections (Sections 7 and 8). The project area of the model may be isolated and used for calibration with appropriate boundary conditions. The full SWM with adjustments for calibration must be used for the final calibration runs to define the impacts of the changes on the entire system. A model calibration report template is included in Appendix B Step 8 - Documentation The modeler must submit a Technical Memorandum (TM) to MSDGC documenting all the changes to the model inputs as well as an analysis of the calibration and validation of the model inputs. Appendix B provides an example of this documentation. Additionally, all updated datasets and model results must be submitted to MSDGC using EPA-SWMM along with any recommended changes to the GIS dataset. Changes to the model input file should be noted generally in the Title section of the input file and in the comment lines of the changed parameters. The necessary documentation is discussed in later sections (Sections 7, 8, and 9) Step 9 - MSDGC Review MSDGC will review the TM and associated datasets, accepting or rejecting proposed changes. Using the work plan as a guide, MSDGC will review the parameters changed, added, or removed from the SWM as well as the resulting calibration. The time required by MSDGC for review and comment of the TM as well as the time required to respond to the comments must be considered in the project schedule Step 10 - Model Alternatives, Evaluation, and Recommendations Once updated and accepted by MSDGC, the SWM model for a project can be used to identify and model potential alternatives. Alternatives must take into account MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 3-5

24 MSDGC REVIEW other projects in as much detail as possible. The specific projects included in the future conditions models will be a matter of coordination with MSDGC and with other consultants. The final alternative details may require coordination with other projects to meet MSDGC system-wide goals. The modeler may use only the project area portion of the SWM, with appropriate boundary conditions, for developing and testing alternatives. The final alternative must be modeled back into the SWM on a broader scale to document the impacts on the system outside the project area. The scale of the SWM modeling depends on the scale of the project and its expected impacts downstream. The portions of the SWM modeled with the final alternative will be coordinated with MSDGC. As discussed in the Section 1, the software used by the modelers for alternative development and analysis does not have to be the MSDGC standard model software. However, the modeler must test the final alternative using the MSDGC standard software and present those results to MSDGC for review Step 11 - New Information Following MSDGC Review of Base Model As MSDGC is likely to have multiple projects simultaneously in each sewershed area, new information should be expected to arise following the approval of the base model. MSDGC and the modeler will review information regarding areas outside the project area based on the expected impact on the project boundary conditions. The modeler will recommend data for inclusion in the model for MSDGC written approval. A cut-off date for model revisions should be set during project negotiations. After this point in the project schedule, no updates to the project model should be made without discussions between the MSDGC project manager, the modeler, and other project team members about the impact of the new information on the project analysis, schedule, and cost. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 3-6

25 DETERMINING IF CHANGES ARE NECESSARY 4. STANDARDS FOR DETERMINING IF CHANGES TO THE MODEL ARE NECESSARY The known information about the MSDGC sewer system is continually changing. Site inspections and surveys clarify details on existing structures. Cleaning and lining may change the roughness of pipes. Pumps are repaired or replaced resulting in changes to the pump curves. New pipes, pump stations, and other structures change system capacity. New development and redevelopment affect dry and wet weather inflows. When updating the model, the updates must be inserted in the model based on the timing of the actual installation. Validation and calibration to observed data may depend on the coordination of the changes to the sewer system and the timing of the observed data. For example, the installation dates of Real Time Control at Ross Run and Mitchell Avenue would change the dates of validation data used for flows in the Mill Creek and Auxiliary Mill Creek Interceptors. Alternatively, correction of the modeled shape of the existing Mill Creek Interceptor is independent of the dates of validation data. 4.1 Existing Conditions Version of the System Wide Model The MSDGC policy is to maintain the SWM as up to date as possible. The SWM is intended to be as correct a representation of the existing sewer system as possible. An accurate model can be used to test and size alternatives to improve operations and reduce overflows. The modeler will update the Existing Conditions SWM whenever discrepancies are found in physically measured parameters according to the model s work plan: Subcatchment o Delineation and area o Percent Slope o Outlet location Pipe o Pipe shape o Diameters and other cross section measurements o Length, inlet and outlet offsets (elevations) Manhole o Type and resulting surcharge depth blind, buried, bolted, etc. o Depth, invert and lid elevation o Area or storage volume Pumps o On and off depths o Pump curves Whenever discrepancies are found in measureable parameters (area, pipe shape, etc.), the modeler will update the Existing Conditions SWM according to the SWM work plan. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 4-1

26 DETERMINING IF CHANGES ARE NECESSARY 4.2 Increased Detail and Model Updates for Project Area As modelers update the existing SWM with information found during successive projects within a sewershed, the existing calibration may be lost. The existing model was originally calibrated by adjusting the model parameters to fit the observed data. If portions of the sewershed above the flow meter site of the observed data are changed, the changes may impact model results (flows, levels, velocities, time of peak, etc.) at the flow meter site. These changes may cause the model to lose calibration with the observed data. The possibility of losing calibration increases with the accumulation of changes to the existing model. Figure 4-1 shows a flow chart indicating guidelines for when a model meets or does not meet validation criterion. This flow chart is primarily intended for small projects that are in unmonitored areas and that are unlikely to impact flows at the nearest flow monitoring site. Projects may require more detailed analysis of the watershed and sewer system within the project area. The issues that may require increased detail include: Smaller subcatchments for modeling flows and water levels within areas of interest Sewer separation Sustainable infrastructure Storage and Real Time Control facilities When defining smaller subcatchments than the original model, design and/or observed storms for a variety of recurrence intervals must be run with both the original and the updated subcatchments. Unless the model is being recalibrated, the original and updated models must have the same response to all storms modeled. This identical response preserves the calibration developed for the original model for areas outside the updated subcatchments. When the model does not meet the validation requirements described in Section 7 and the model must be adjusted, the model will be updated to better represent the sewer system. The model will be updated to the information matching the time period of the validation data. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 4-2

27 DETERMINING IF CHANGES ARE NECESSARY Figure 4-1 Flow Chart for Achieving Validation MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 4-3

28 GENERAL MODELING METHODOLOGY 5. GENERAL MODELING METHODOLOGY This section of the SWM Modeling Guidelines & Standards presents the requirements for the overall modeling effort. For specific situations, modelers may vary from these requirements with approval from the PBD Modeling and Monitoring Group. 5.1 Standards for General Modeling Methodology This document contains both guidelines and standards. Guidelines give the modeler a reference to aid in decision making. Standards are the values and methods expected by MSDGC and should be followed unless satisfactory justification can be provided by the documentation. Both the standards listed in this section and the available guidelines are discussed in the following text. Table 5-1 lists the model properties that are considered standards. 5.2 Data Quality Review Modelers should review data used in the model input files, including the data sources describing the physical network (i.e., GIS data, surveys, as-built drawings) as well as the calibration data (rain, flow, level, velocity, pump records, gate operations, etc.). The limits of the model review depend on the scope of the project. For each project, these limits will be determined during the project scope negotiations Flow Data Reliable flow monitoring data is necessary for the development of an accurate hydraulic model. Initial model development should include an assessment of flow monitoring data, including: depth-flow scatter plot, depth-velocity scatter plot, as well as the assumed pipe size and shape for the flow calculations. The modeler should work with MSDGC to identify available flow monitoring and rainfall data and to review GIS data. If flow monitoring data are not available or are insufficient, identify the need for flow monitoring and potential locations and submit this recommendation to MSDGC. Insufficient data includes flows collected only during: 1. Unusually wet or dry periods with abnormal rainfall-to-runoff characteristics. 2. Periods with only small storms (if calibrated only to small storms, the model may poorly simulate larger storms). 3. Periods before major system changes (major change in land use, sewer separation, RTC, etc.) such that the flows do not correspond to the modeled collection system. 4. Periods of data with large or frequent gaps (poor data quality), so peak flows or water levels are missed or volume calculations may not be complete. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-1

29 GENERAL MODELING METHODOLOGY Table 5-1 General Modeling Methodology Standards Topic Model Option Standard General Options Infiltration Horton s method Ponding at Nodes No Ponding Inertial Terms Dampen Supercritical Flow Slope and Froude number Dynamic Wave Force Main Equation Hazen-Williams Variable Time Steps On Conduit Lengthening 10 seconds Minimum Surface Area Default ( ft 2 ) Dates End of Analysis Return to DWF Time Steps Routing Time Step 5 seconds Boundary Conditions Files Not used in MSDGC submission Boundary Conditions Boundary Conditions by Not used without MSDGC others Project Manager permission Hot Start files Not used in MSDGC submission Modeling Units Modeling Units See Table 5-2 Evaporation Evaporation Data See Table 5-3 Hydrology Subcatchment Area Always correct area Subarea Routing Outlet Outfall Normal depth Dry Weather Flow pattern Use diurnal and weekly pattern but not seasonal Energy Loss at bends See Figure 5-2 Energy Loss at drop Use 1.0 on entrance of manhole downstream pipe Hydraulics Modeling of pump Most realistic pump possible, not Ideal pump Modeling pump wet well Use storage node of realistic dimensions Modeling of force main Use force main or gravity conduit as appropriate Weir coefficient Sharp crested (CSO dam) 3.33, Inflatable dam 2.5 The primary limitation in flow monitoring for calibration data is the possible inaccuracy in the flow measurement. This inaccuracy can be ±10% or more, resulting from errors in the level measurement, the velocity measurement, and the pipe cross section measurements. These three measurements are used in each instantaneous calculation of flow, so small errors (on the order of 2%) in each MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-2

30 GENERAL MODELING METHODOLOGY measurement combine to become a larger error. As the depths or velocities approach or exceed the limits of the instrument, the errors will increase. MSDGC has procedures in place for the initial review of rain and flow monitoring data. Because of the volume of data regularly collected by MSDGC, this review will never be as comprehensive as a review by modelers investigating a specific area and period of time. The modeler is expected to review the available data to identify periods of data for use in modeling. For flow and level data, the data review should include: Conservation of volume through downstream monitors; Extreme changes in depth, velocity, and/or flow; Extreme values of depth, velocity and/or flow; Depth or velocity measurements outside range of instrument; Scatter plots of depth to velocity and depth to flow for consistency; Periods of supercritical flow and hydraulic jumps; Periods of receiving water intrusion Flow monitoring data standards are currently being developed in a separate effort. The results of that effort will be reflected in revisions to this document Rain Data Rain gauges supply precipitation data for one or more subcatchments within the study area. The rainfall data can be either a user-defined time series or reference an external file. The primary input properties for rain gauges are the rainfall data type and recording time interval. EPA-SWMM has three options for the rainfall data type: intensity, volume, or cumulative. MSDGC normally uses the volume rainfall data type that records the incremental rainfall (in inches) at a specified time step. This choice is to reduce the possibility of rainfall data errors when switching between observed data and design storms (frequently intensity). Rain gauge site selection is an important aspect of model development. The lack of data about the spatial variability of rainfall and problems with rain gauges can cause many problems with model calibration and validation. Flow monitoring data standards are currently being developed in a separate effort. The results of that effort will be reflected in revisions to this document Radar Rainfall MSDGC utilizes weather radar technology in association with rain gauges to observe and record rainfall. Provisional hourly rainfall estimates, in inches, over Hamilton County is available through the MSDGC website. Complete data sets that have undergone a QA/QC review are available through data request to MSDGC. The radar data is supplied as incremental rainfall at grid points radiating from the National Weather Service (NWS) Wilmington radar site. Each grid cell is approximately 1 kilometer (km) by 1 degree (roughly 1.3 km in Hamilton County). MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-3

31 GENERAL MODELING METHODOLOGY Radar rain data can be used in one of two ways point or subcatchment average rainfall. The point method assigns the rainfall calculated for the grid cell of the subcatchment centroid. The subcatchment average method uses the average rainfall of all the grid cells that fall within the subcatchment delineation. While requiring more effort, the subcatchment average method produces more representative data than point rainfall data Thiessen Polygon Method The Thiessen polygon method assigns areal significance to point rainfall values, such as the data collected by rain gauges. In this method, perpendicular bisectors are constructed to the lines joining each measuring station with those immediately surrounding it. The bisectors form a series of polygons, with each polygon containing one station. The value of precipitation measured at a station is assigned to the whole area covered by the enclosing polygon. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-4

32 GENERAL MODELING METHODOLOGY Figure 5-1 shows an example of Thiessen polygons. This method is useful for determining which subcatchments to assign to a particular rain gauge in a model. The subcatchment area centroid is calculated in the GIS software from the subcatchment delineation. The subcatchment is then assigned the rainfall total corresponding to the center of the Thiessen polygon Single Rain Gauge or Design Storm If only a single rain gauge is used for the project area or when using a design storm, all subcatchments use the same rainfall data set GIS In this document, the term GIS refers generically to GIS maps and geospatial data and to the Cincinnati Area GIS (CAGIS) shapefiles. CAGIS shapefiles include system attributes beyond the geospatial data. An example is the CAGIS msdsewer shapefile, which includes such information as pipe length, shape, size, material, slope, and inverts. Model developers should use GIS records as a source of information. However, in cases where GIS data are incomplete or incorrect, discrepancies should be resolved through information requests to MSDGC or field visits. GIS standards are discussed in the work plans in Appendix A Field Verification During model development, field verification may be needed to obtain an accurate understanding of the structure or operation of the system being modeled. Field verification could include site visits and inspections, flow monitoring, smoke and dye studies, geotechnical investigations, and/or detailed surveys. The data quality standards are described in the SWM Work Plan. Any measured data used to update the SWM will be documented as described in Section 9. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-5

33 GENERAL MODELING METHODOLOGY Figure 5-1 Thiessen Polygon for Rain Gauges Survey vs. Measurement When performing field verification, measurements of structural attributes of the sewer (i.e., manhole depths, pipe sizes, dam height, etc.) will be taken. The modeler can use these measurements to resolve inconsistencies in the model. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-6

34 GENERAL MODELING METHODOLOGY For the purpose of updating GIS data, a licensed surveyor may be required to perform the field verification to ensure accuracy. For clarification on this topic before proceeding, coordinate the data request with the appropriate MSDGC personnel Coordination with MSDGC To avoid redundant efforts, modelers should coordinate any field verifications as well as any subsequent changes with the MSDGC PBD Modeling Group. Other projects or departments within MSDGC may have already collected relevant data. 5.3 General Model Options The options tab of the EPA-SWMM software sets the overall modeling options. The following sections describe the MSDGC settings required Infiltration Method EPA-SWMM allows the use of only one infiltration method throughout the model. MSDGC has chosen to use the Horton method of modeling infiltration Ponding at Nodes Ponding is the storage of water that is modeled as overflowing out of the top of a node. If ponding is used, the overflowing water is stored at the node and returned to the system as capacity allows. If ponding is not used, the overflowing water is lost from the system. MSDGC standard practice is to not allow ponding for modeling on a system wide basis. The possible destination of overflow water varies with the specific location of a manhole. As EPA-SWMM requires all or none of the manholes have ponding and individual ponding manholes can be modeled in other ways, not allowing ponding is the more accurate choice. However, if field data indicate that ponding occurs, the modeler should update the affected nodes. In the MSDGC service area, water overflowing from manholes has several possible fates. The first fate is for the overflowing water to flow to a natural channel or storm sewer system that is not included in the SWM. This flow would be lost from the modeled system. The second fate is ponding, as modeled by EPA-SWMM. Water ponds above the overflowing manhole and returns to that manhole as sewer capacity allows. Because the MSDGC standard is for no ponding system wide, ponding is modeled using individual manhole parameters. The third fate is for overflowing water to leave the overflowing manhole but return to the sewer system at another location. The return to the sewer system may be through street flows to a catch basin, through a natural channel that enters the sewer system, or into a storm sewer that is part of the modeled system. Depending on the required level of accuracy of modeling required, how far the overflow travels before re-entering the sewer, and whether the overflow returns to the same sewer line, these situations may be modeled in one of two ways. The first MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-7

35 GENERAL MODELING METHODOLOGY way is for situations where the overflowing manhole and receiving manhole are in proximity and on the same sewer line. For this case, the ponding and return is modeled at the overflowing manhole. An example of this situation is an overflowing manhole located a block uphill of a catch basin on the same combined sewer line. The second way is to model flows that travel a significant distance before returning to the modeled system or return to the system somewhere other than downstream of the overflowing manhole. To model this situation, add the street, natural channel, etc. to the model. In this case the overflowing and return manholes have the estimated depth of flow added to their manhole depths. The conveyance is modeled to carry the overflow to the return manhole Dynamic Model Routing Dynamic routing will be used for modeling with the SWM, as it produces the most accurate results. This method models time and location varying flow, backwater and reverse flow effects, pressurized flow, and entrance and exit losses. For EPA-SWMM , the default settings are standard for the SWM: Inertial terms are Dampen Supercritical flow is determined by both slope and Froude number Force main equation is Hazen-Williams Variable time steps are used Conduit lengthening uses 10-second time of travel Default minimum surface area is used Time Frame of Model Run - Dates The time frame for the model run is specified in the Simulation Options tab. The modeler is required to specify the Start of Analysis, the Start of Reporting, and the End of Analysis Time Period Before Recording Results Start of Analysis At the beginning of a model run, a period of model time is required to stabilize the flows, water levels, etc. During this period, the dry weather flows have time to reach the outlet of the model, storage volumes and pump rates reach quasi-equilibrium, and control rules are operated to normal settings. As the model output for this period of stabilization is unreliable, the output should not be saved for use in analysis. The length of time before the model begins to save data results is the difference between the Start of Analysis and the Start of Reporting. Setting this time period balances the time required for the software to model this period and the possibility of instabilities being saved in the model output. One method to estimate the required time period is to use the speed a gravity wave or a particle of water would travel from the farthest inflow node to the outlet. An approximate estimate of these speeds is 3 feet per second (fps). MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-8

36 GENERAL MODELING METHODOLOGY The length of time needed to stabilize the model may be reduced using either hot start files or initial conditions values for each hydraulic element. These techniques are discussed below Time Period Before Rainfall Start of Reporting A period of dry weather flow should be established before rainfall occurs in a model simulation. When performing calibration or other model analysis, this period allows review of the hydrograph starting at base conditions. For watersheds with diurnal or other flow patterns, at least one full cycle should be included in the period before the rainfall begins. This suggestion is to aid the viewer of the hydrograph in judging the significance of the runoff peak flow and volume relative to the range in dry weather flow. This period is determined by the Start of Reporting. The preferred Start of Reporting is midnight so as to begin hydrographs at the presumed lowest dry weather flow if a diurnal pattern is used. Additionally, this start time is easily understood by the viewer of the hydrograph Time Period Following Rainfall End of Analysis The modeled flows return to dry weather flow after rainfall occurs. When performing calibration or other model analysis, this period allows review of the hydrograph shape (timing and rate of decrease) as it returns to base conditions. The modeled flow should return to dry weather flow for one diurnal cycle. This period is determined by the End of Analysis. The preferred End of Analysis is midnight so as to end hydrographs during a period of lower dry weather flow if a diurnal pattern is used. Additionally, this end time is easily understood by the viewer of the hydrograph Time Step for Model Run Time steps are the length of time used for runoff and routing computation as well as results reporting. Time steps are specified in days, hours, minutes, or seconds Reporting Time Step The reporting time step should be set to approximately the same increment as the available observed data. MSDGC normally records data at 5-minute intervals for flow data and rainfall data. Other data sources, such as USGS and NWS, may use other time steps, such as 15 minutes or 1 hour. For more information, see the MSDGC Flow Monitoring Standards. For the Typical Year, the default time step is 1 hour to match the rainfall data. For design or observed storms, the time step is 5 minutes or the interval of the rainfall time step. For projects investigating more detailed operations, such as RTC and pump stations, the recording time step should match the calibration data. For investigation of rapidly changing situations, the recording time step may be very small. Certain situations, such as RTC inflatable dams and automated gates, may require very small recording times steps to enable review of modeled operations. In MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-9

37 GENERAL MODELING METHODOLOGY modeling a specific event, the recording time step may be as small as the 5-second routing time step Runoff Time Step Both the Dry Weather and Wet Weather Runoff Time Steps should be set equal to the Reporting Time Step, which in turn is set to approximately the observed data time step Routing Time Step The routing time step initially should be set to 5 seconds. The duration can be reduced to help with instability in the model. Decreasing the routing time step reduces instabilities but increases model run time Boundary Condition and Hot Start Files Boundary condition files are used to reduce the size and run time of models by providing data (flows, levels, etc.) instead of requiring the model to calculate the data every model run. Boundary condition files speed the development and testing of alternatives, and reduce the possibility of corrupting portions of the model outside the project boundaries. Boundary conditions files are allowed for alternative development by MSDGC to increase efficiencies. For final runs of the project models for documentation and submission to MSDGC, boundary condition files cannot be used. As separate files from the model input file, boundary condition file management adds complication to modeling by others. In addition, the boundary location may be influenced by either the existing conditions or the alternatives developed. In this case, running the full model instead of using the boundary conditions is the correction to possible errors in boundary location selection. When the boundary condition files are generated by MSDGC or other organizations to represent future project impacts, the modeler uses the provided data. The modeler does not need to acquire and incorporate the proposed changes. The modeler is required to document the source of the data, the date of data delivery, and a description of assumptions used. The use of boundary conditions data from other sources must be authorized by the MSDGC project manager. When an interceptor is the downstream boundary condition, the Typical Year time series should be used as the boundary condition. The surcharge condition of the interceptor may limit the underflow capacity and impact the CSO volume. At a minimum, the recommended condition for an interceptor is full pipe, unless other information is available. Hot start files provide the flows and water levels throughout the model for stable conditions (such as dry weather flow) without the delay of running the model for an extended period before the Start of Reporting. However, the hot start file must be recreated when hydraulic elements are added, removed, or renamed. While hot start files may be used for alternative development, they cannot be included for the MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-10

38 GENERAL MODELING METHODOLOGY submission to MSDGC. The extra file management and the requirement for a new hot start file for changed hydraulic networks complicate the use of the model by others. 5.4 MSDGC Modeling Units SWMM can use either US or SI metric units of measure. The unit system that is used for all quantities is determined by selecting flow units. Flow units can be selected directly from the Status Bar on the main window or by setting a project s default values. If the change is made in the project s default values, the selection can be saved so that all future projects will automatically use those units. Care must be taken when changing units for an existing model. The units will change, but the values may not. For example, if changing from million gallons per day (mgd) to cubic feet per second (cfs), the maximum flow in a pump curve (for example, 10 mgd) will not change values (10 cfs not the correct cfs). MSDGC standard practice is to use cfs-based units, as shown Table Evaporation Evaporation can significantly affect runoff, especially during the Typical Year or other continuous simulations. Evaporation reduces the amount of runoff by depleting the depression storage between rain events. Evaporation is required to be modeled for single event or design storm modeling as well as continuous period modeling. This practice reduces the chance of not incorporating evaporation for continuous period modeling when switching between event modeling and continuous period modeling. MSDGC s preferred method for modeling evaporation is to use the literature values for evaporation. For multiple event or continuous period modeling of specific time periods for which observed data is available, evaporation from calculations is allowed. For example, an abnormally warm March may encourage the growth of vegetation that would increase the evapotranspiration. The term evaporation used in EPA-SWMM is actually potential evapotranspiration. Evaporation only occurs when the subcatchment surface (depression storage) or storage unit has water to evaporate. MSDGC standard practice is to use the literature values listed in Table 5-3 for all modeling. MSDGC standard practice is also to check on the Evaporate Only During Dry Periods option of the Evaporation tab of the Climatology window as being more representative of the normal evaporation. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-11

39 GENERAL MODELING METHODOLOGY Table 5-2 Standard Units Variable Units Infiltration Infiltration Rate Inch per hour (in/hr) Decay Constant hours -1 (1/hr) Drying Time Days Climatology Evaporation Inch per day (in/day) Rainfall Inches (in) Subcatchments Area Acres (ac) Width Feet (ft) Depression Storage Inches (in) Slope Percentage (%) Imperviousness Percentage (%) Unit Hydrograph Maximum Depth Inches (in) Recovery Rate Inch per day (in/day) Initial Depth Inches (in) Nodes Invert elevation Feet (ft) Maximum Depth Feet (ft) Initial Depth Feet (ft) Surcharge Depth Feet (ft) Ponded Area Square Feet (ft 2 ) Conduits Maximum Depth Feet (ft) Length Feet (ft) Inlet Offset Feet (ft) Outlet Offset Feet (ft) Initial Flow Cubic feet per second (cfs) Maximum Flow Cubic feet per second (cfs) Transect Editor Station Feet (ft) Output Results Flow Cubic feet per second (cfs) Velocity Feet per second (fps) Runoff Results Total Precipitation Inches (in) Total Runon Inches (in) Total Evaporation Inches (in) Total Infiltration Inches (in) Total Runoff Inches (in) Total Runoff Volume Million Gallons (MG) Peak Runoff Cubic feet per second (cfs) Storage Unit Volume 1000 Cubic feet (ft3) MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-12

40 GENERAL MODELING METHODOLOGY Evaporation from Literature The evaporation data shown in Table 5-3 was obtained from NOAA Technical Report NWS 33, Evaporation Atlas for the Contiguous 48 United States, U.S. Department of Commerce, Washington, D.C., June 1982, as reported in the Natural Resources Conservation Service (NRCS) Electronic Field Office Technical Guide ( Table 5-3 Monthly Pan Evaporation for Hamilton County, OH Monthly Total (inch) Rate (in/day) January February March April May June July August September October November December Total Evaporation from Calculation MSDGC standard practice is to use the values in Table 5-3 but calculated evaporation may be used in specific circumstances. The primary issues with calculating evaporation are the selection of the equation and collection of the required data. The number of variables used in calculating evaporation varies with the method. The Hargreaves method (used in EPA-SWMM and later) uses the observed daily maximum and minimum air temperatures as well as the site latitude. The Priestly-Taylor method uses solar radiation, air temperature, and relative humidity. The Penman-Monteith method uses solar radiation, air temperature, relative humidity, and wind speed. The accuracy of these equations depends on how well they represent the physics of evaporation and on the accuracy of the data used. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-13

41 GENERAL MODELING METHODOLOGY While using the evaporation equations may represent the conditions for observed storms, the input data for the evaporation equations would have to be developed to represent the normal conditions throughout the Typical Year or for design storms. MSDGC may determine that evaporation estimates from normal temperatures are more representative. 5.6 Hydrology MSDGC uses two methods within EPA-SWMM to calculate the rainfall-derived flow into the sewer system: surface runoff (subcatchments) and rainfall-derived inflow and infiltration (RDII). The surface runoff method is used in combined sewer areas and in stormwater sewer areas. The RDII method is primarily used in the separate sanitary sewer areas. The RDII method can be used in combined sewer or stormwater sewer areas if observed data indicate additional flows that cannot be accounted for with the calibrated surface runoff EPA-SWMM Surface Runoff Methodology A subcatchment surface is treated as a nonlinear reservoir. The inflow consists of precipitation and runoff from subcatchments upstream. The outflow consists of infiltration, evaporation, and surface runoff. The subcatchment acts as a reservoir with a capacity equal to the maximum depression storage, which is the maximum surface storage provided by ponding, surface wetting, and interception. Surface runoff from the depth of water over the subcatchment exceeds the maximum depression storage. SWMM continuously updates the depth of water over the subcatchment by repeatedly solving a numeric water balance equation Subcatchments Subcatchments are represented in the model as hydrologic units whose topography and drainage system components direct surface runoff to a single discharge point. The MSDGC service area has been modeled with sufficient subcatchment coverage. For project modeling, the subcatchments may be adjusted to improve accuracy, to better represent flow paths, or to include new or changed infrastructure. Examples of when the existing subcatchments may be changed include: Redefinition of flow paths Projects examining flows within subcatchment Flow monitoring within subcatchment Subdividing subcatchments to account for differing land use, slope, etc Allowable Changes to Hydrologic Parameters The subcatchment parameters can be measured or estimated to varying degrees of accuracy. For example, the percent impervious area is very difficult to accurately measure for large areas. Determining the number and area of roofs draining to pervious areas would require an extensive field program. Finding which paved areas flow to pervious areas also would require a field program. As this parameter has a MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-14

42 GENERAL MODELING METHODOLOGY large degree of uncertainty, adjusting the percent impervious as a first step to improve model calibration is required. Conversely, impervious surface roughness is a better estimated parameter, as the types of impervious surfaces and their approximate Manning's n value can be accurately estimated from orthophotos. Because this parameter has a low degree of uncertainty, adjusting this parameter is expected to be limited as guided by Table 5-4. A recommended (but not required) hierarchy of adjustment priority is: 1. Percent impervious 2. Width 3. Slope 4. Depression storage 5. Maximum infiltration rate 6. Minimum infiltration rate 7. Percent zero impervious depression storage 8. Surface roughness 9. Subarea routing The only subcatchment parameter that MSDGC does not allow changes to (unless the modeler is certain the existing model is incorrect) is the total area of the subcatchment. Subcatchments may be subdivided, joined, or added but the total area of the watershed must be correct and accounted for in the SWM. If subcatchment area is changed, the width also must be changed to maintain the flow path length calculated from the area and width values. The change in the width is proportional to the change in area. A 10% increase in subcatchment area is matched by a 10% increase in width Width The width parameter is based on the length of the overland flow path for sheet flow runoff in a subcatchment. An initial estimate of the width can be determined by dividing the subcatchment area by the average overland flow length. The overland flow length is the length of the flow path from the farthest drainage point of the subcatchment to the point where the flow enters a pipe, stream, gutter, or other conveyance. Multiple flow path lengths should be measured for each subcatchment to develop the initial area-weighted average value. Generally, flow path lengths are on the order of 100 to 300 feet in developed areas and less than 500 feet in undeveloped areas. In the model, the width parameter best represents the physical process of flow attenuation and, therefore, adjustments should be made to the width parameter to improve the modeled hydrograph shape compared to the measured hydrograph Slope The slope parameter is the steepness of the overland flow path and is given in percent slope. Average percent slope values can be estimated by taking the average elevation difference in the subcatchment and dividing it by the maximum overland MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-15

43 GENERAL MODELING METHODOLOGY flow length. The impervious and pervious surfaces use the same slope within the EPA-SWMM software. Adjustments to the slope subcatchment parameter affect the timing of the runoff from a subcatchment and, therefore, are used to adjust the time to peak and duration of the runoff hydrograph Percent Impervious Subcatchments are divided into pervious and impervious subareas. Surface runoff can infiltrate into the upper soil zone of the pervious subarea but not through the impervious subarea. Adjustment to the percent impervious parameter has the most significant impact on the volume of runoff from the subcatchment. Percent Impervious values can be determined using GIS or estimated from land use. Determination from GIS may be more accurate for a specific subcatchment, as it accounts for individual circumstances such as large parking areas or highways within the subcatchment. By accounting for these details in the initial setup of the Percent Impervious, the modeler may require less iterations to achieve calibration Hydraulically Connected Impervious Area The impervious area is assumed to be hydraulically connected to the outlet point of the subcatchment. The meaning of this assumption is that small areas of imperviousness flowing onto pervious surfaces act as part of the pervious area. Examples include roofs draining to large pervious areas, as well as sidewalks and patios draining to yards. Subarea Routing is used to adjust the internal routing of runoff between pervious and impervious areas. The three options for Subarea Routing are: Imperv, where the runoff flows from the impervious to the pervious area; Perv, where the runoff flows from the pervious to the impervious area; and Outlet, where the runoff from both areas flows directly to an outlet. The Percent Routed is used to adjust the amount of runoff routed between subareas. MSDGC normally uses Outlet which assumes the impervious areas are hydraulically connected to the outlet. Detailed models of small subcatchments may use other routing methods as needed GIS Calculation The modeler can use GIS to analyze the land use of a subcatchment, as well as measure impervious properties such as roads, pavement, and roof area. Within each catchment, the different forms of impervious area are measured. A factor should be developed to account for the fraction that flows to pervious areas for that type of imperviousness. An example would be that 50% of roof areas less than 2,000 ft 2 are assumed to be houses with downspouts discharging onto yards. Roof areas greater than 2,000 ft 2 are assumed to be commercial or other large structures discharging to the combined sewer. When the various type of impervious areas are factored and summed to produce the subcatchment percent impervious, the result will be compared to the literature values listed below as check on reasonableness. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-16

44 GENERAL MODELING METHODOLOGY The GIS calculation can be supplemented with field data. The level of detail can vary from a windshield survey of a portion of the sewershed to inspection of every impervious surface. From the field survey, the modeler can refine the Subarea Routing and Percent Impervious values to better represent the subcatchment Literature Value Literature values for percent impervious area have been developed as a guide for modelers as shown in Table 5-4. These values are general averages and should be viewed as starting values. Factors that may adjust the percent impervious include: Extent roofs are routed directly to storm or combined sewers Use of ditches rather than gutters for stormwater Amount of landscaping around office complexes and parking lots Stormwater detention ponds allowing infiltration and evaporation Park facilities such as parking lots, tennis and basketball courts, picnic shelters Calibration is likely to require adjustment of these values to achieve acceptable results. Table 5-4 Percent Impervious by Land Use Land Use Percent Impervious Commercial/Industrial 90 Institutional 90 Parking 95 Multi-unit Residential 75 Residential 0.25 acres per house acres per house acre per house acres per house 10 Open Land 5 Forest Surface Roughness Using Manning s n Subcatchments require input of Manning s roughness n for both pervious and impervious subareas. During the calibration process, Manning s n values can be adjusted to affect the timing and attenuation of the runoff from the subcatchment without impacting the runoff volume. However, significant changes to the referenced Manning s n values listed below most likely indicate that other parameters should be MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-17

45 GENERAL MODELING METHODOLOGY adjusted, such as depression storage or slope. Generally, adjustments to Manning s n values are expected but not required to remain in range of 20% of the values shown in Table 5-5. Table 5-5 Manning's Roughness n for Overland Flow Surface n Smooth asphalt Smooth concrete Ordinary concrete lining Corrugated metal pipes Cement rubble surface Fallow soils (no residue) 0.05 Cultivated soils Residue cover < 20% 0.06 Residue cover > 20% 0.17 Range (natural) 0.13 Grass Short, prairie 0.15 Dense 0.24 Bermuda grass 0.41 Woods Light underbrush 0.40 Dense underbrush 0.80 Source: McCuen, R. et al. (1996), Hydrology, FHWA-SA , Federal Highway Administration, Washington, DC Depression Storage Depression storage is the maximum surface storage provided by ponding, surface wetting, and interception. Adjustments to the depression storage can affect the volume of the runoff hydrograph as well as timing of the beginning of the hydrograph. As previously mentioned, subcatchments are divided into pervious and impervious subareas. Surface runoff can infiltrate into the upper soil zone of the pervious subarea, but not through the impervious subarea. Impervious areas are further divided into two subareas: one that contains depression storage and another that does not. Similar to the Manning s n values, during calibration depression storage values can be adjusted to affect the volume and timing of the runoff hydrograph from the subcatchment. However, significant changes of referenced depression storage values most likely indicate that other parameters should be adjusted. Generally, adjustments to depression storage values should remain in the range of 20% of the values shown in MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-18

46 GENERAL MODELING METHODOLOGY Table 5-6. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-19

47 GENERAL MODELING METHODOLOGY Table 5-6 Typical Depression Storage Values Surface Impervious surfaces Lawns Pasture Forest litter Depth of Storage inches inches 0.20 inches 0.30 inches Source: ASCE, (1992), Design & Construction of Urban Stormwater Management Systems, New York, NY Infiltration Method Infiltration is the process of rainfall penetrating the ground surface into the unsaturated soil zone of pervious subcatchment areas. SWMM offers three options for modeling infiltration: Horton s Equation, Green-Ampt Method, and the Curve Number Method. The infiltration method is chosen in the General Tab in the Simulation Options. SWMM 5 only allows a single infiltration method to be chosen for a model. MSDGC uses the Horton s Equation method to calculate infiltration. The Horton method has four required parameters and a fifth optional parameter: maximum and minimum infiltration rates, decay curve, drying time, and the optional maximum infiltration volume. Table 5-7 lists the expected range of values for the Horton method in Hamilton County. Table 5-7 Infiltration Parameters Infiltration Expected Range Units Description Parameter of Values Maximum In/hr Fully dried soil 1 to 3 Infiltration Rate Minimum In/hr Fully saturated soil 0.1 to 0.25 Infiltration Rate Decay Rate Hr -1 Transition from Max to Min infiltration rate 2 to 4 (SWM usually 2) Drying Time Days Time to return to Max infiltration rate Maximum Infiltration Volume Inches Optional capacity of soil, no infiltration once reached 5 to 10 (SWM usually 7) 3 to 10 inches depending on depth of soil The maximum and minimum infiltration rates are initially determined from literature values or from NRCS soil mapping estimates. These values may be adjusted to impact the timing of the start of the hydrograph, the peak runoff rates, and the shape of the hydrograph recession. When adjusting infiltration rates, the adjusted rates may MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-20

48 GENERAL MODELING METHODOLOGY change by 50% but should be compared to the literature values and soil mapping. Because of the presence of clay soils and the large areas of development and compaction, most subcatchments should have low infiltration rates. High infiltration rates should be expected only in areas with sand deposits, such as stream beds and some filled areas. Table 5-8 may serve as a guide to expected maximum infiltration rates (hydraulic conductivity in table) when more detailed data are not available. The decay curve and drying time determine the rates at which the soil infiltration changes from maximum to minimum rates and back. The decay curve value should be approximately 2 hr -1, which indicates a clay soil that quickly swells and limits infiltration. The drying time should be approximately 7 days, which indicates clay soils that dry slowly. The maximum infiltration volume (volume per unit area with units of depth) determines when the soil is saturated and no longer accepts infiltration. This value is determined using a large number of storms and is not normally used by MSDGC. This parameter may be used more frequently in modeling sustainable infrastructure with surface layers of high infiltration, porous backfill for storage, and very low infiltration rates for sub-soils beneath sustainable infrastructure. Table 5-8 Soil Characteristics Soil Texture Class K FC WP Sand Loamy Sand Sandy Loam Loam Silt Loam Sandy Clay Loam Clay Loam Silty Clay Loam Sandy Clay Silty Clay Clay K = hydraulic conductivity, in/hr = suction head, in = porosity, fraction FC = field capacity, fraction WP = wilting point, fraction Source: Rawls, W.J. et al., (1983). J. Hyd. Engr., 109:1316. The Maximum Infiltration Volume is estimated from soil data based on the field capacity and depth of soil. The information for estimating the volume is found at the NRCS Soil Data Mart ( using the Physical Properties report. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-21

49 GENERAL MODELING METHODOLOGY 5.7 Hydraulic Network The hydraulic network (pipes, manholes, orifices, weirs, pumps, etc.) can be reviewed through GIS and other data sources to verify that the parameters are reasonable and represent the physical reality Nodes Nodes represent a collection point in a hydraulic network. Nodes in SWMM are categorized into four types: junctions, outfalls, dividers, and storage units. Several parameters are used by most of the node types. Depth of the node is the distance from the node invert to the ground surface. This value can be determined from GIS data or field measurements. Initial depth is the depth of water in a manhole prior to simulation. This parameter may be used to speed stabilization of the model at the beginning of a model run instead of a hot start file. Surcharge depth is the depth above the rim elevation before which water floods. Surcharge depth is often added for bolted manholes and for blind junctions to prevent overflows (flooding) from the node. When a blind manhole is modeled, a surcharge depth input value should be set so high so that the node will never flood. The value used should be an easily recognizable round number that is much higher than any expected ponding in the MSDGC service area. The recommended surcharge depth is 50 feet. The following sections provide more detail on the different types nodes located in the model Junctions The most common nodes in a SWMM model are junctions, which represent simple manholes. Junctions are assumed to be ft 2 unless changed in the Options menu, Dynamic Wave tab, Minimum Surface Area parameter field. The default value is used if the parameter field is 0. If volume is required to accurately represent the physical structure or if additional storage is needed to stabilize the model, a storage node is substituted for the junction Outfalls An outfall is a node without a pipe on the downstream end. Outfalls usually represent an exit point in the system, such as the outfall of a CSO. Five different types of outfalls are defined in EPA-SWMM: free, normal, fixed, tidal, and time series. When using elevation or level data for the outfall, the modeler should verify that the datum used in setting the level is appropriate in comparison to the model outfall elevation. The first type is a free outfall, which has no governing downstream conditions for the outfall so the flow regime passes through critical flow. This type of outfall is not normally used, as the critical flow at the downstream end may overstate pipe capacity. This outfall type may be used for a particular situation known to be a free outfall. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-22

50 GENERAL MODELING METHODOLOGY A normal outfall uses the normal depth of flow at the downstream end of the discharging pipe. Normal flow is the most likely situation for an outfall discharging to a channel. Normal flow is also a compromise between modeling a free outfall to a channel during low flow and small events, and estimating a backwater condition for high flows in the receiving stream during large events. Other outfall types would require some information on the particular outfall, such as frequency and extent of backwater in the receiving channel. A fixed outfall sets the depth or stage of the boundary condition for the downstream end of the outfall. This type of outfall produces more realistic flow conditions in the discharging pipe than the free outfall if the selected depth is appropriate. The tidal outfall curve is capable of setting the boundary condition based on the time of day, which is mostly useful when dealing with high tide and low tide of the ocean, an issue not considered in Cincinnati. The time series outfall is a user-defined series that represents the stage of the boundary condition for a certain day and time. If reliable data are available for the stage of the Ohio River, the Mill Creek, Little Miami River, Great Miami River, or other streams, the water surface elevation may be input to examine the interaction between the MSDGC system and surface waters. The USGS has stream gauge data at The gauges that may be of interest include: Ohio River at Cincinnati ( ) Mill Creek at Evendale ( ) Mill Creek at Sharonville ( ) Mill Creek at Reading ( ) Sharon Creek at Sharonville ( ) Little Miami River at Milford ( ) Great Miami at Miamitown ( ) When using stream gauge data, the modeler must consider the distance to the measurement site and flows occurring between the measurement and the location of interest. For example, the water surface elevation at the Muddy Creek WWTP will be lower than at the Ohio River at Cincinnati gauge, but will also be influenced by backwater caused by flows from the Great Miami River entering the Ohio River. Additional stream water levels may be available at the outfalls of the RTC facilities, at the WWTP, and for CSO and SSO overflow monitors. Caution should be used with these data sources as the gauges are generally intended for purposes other than stream level monitoring. Site-specific hydraulics may limit the usefulness of the data (e.g., RTC outfall measurements at CSO 487 Ross Run actually measuring depth of flow from the RTC). In this case, review of the RTC operational data may indicate when the RTC dam was storing water and the RTC outfall data reflects the water level in the Mill Creek. MSDGC standard practice is to use the normal depth outflow as producing more realistic flows in the discharge pipe unless specific site information is available. Specific information would include site visits to verify possible pooling at the end of MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-23

51 GENERAL MODELING METHODOLOGY an outfall, cross sectional data for downstream channels, or any other hydraulic situation that would inhibit normal flow depths Dividers The divider is similar to a node with many of the same input parameters except a divider can split the flow if multiple downstream links exist. Dividers were commonly used to model CSO regulators when the model was run with a kinematic wave solution. Dividers can only be used with kinematic wave; the dynamic wave solution treats dividers as a regular node. MSDGC standard practice is to not use dividers, as the SWM models with dynamic wave. Limiting flow through a particular pipe is possible using the maximum flow parameter in a conduit Storage Units Storage units are nodes that have storage capacity that can range from the inherent storage in a catch basin, a storage tank, or a retention pond. The storage volume can be entered as: Fixed plan area throughout the depth of the storage like a pump station wet well Curve equation for smooth shapes like a surface pond Table of values for variable shapes like a storage tank For ponding at an overflowing (flooding) manhole that returns flow to the same manhole, the ponding can be modeled using the table of values. The storage of the manhole with depth can be inserted in the table as well as the storage from surface flooding. The depth of the manhole would have to be increased to account for the depth of storage modeled. Evaporation from a storage unit is available using the evaporation factor, ranging from 0 (closed tank) to 1 (shallow open pond), which represents the evaporation potential in the basin. This feature allows for modeling the evaporation from sustainable infrastructure. 5.8 Inflows to Nodes Nodes are the locations where flows are added to the hydraulic system. Flows can be from subcatchment runoff, dry weather flow, RDII, and direct flows (outside calculations) Subcatchment Runoff Flows from subcatchments are calculated by the model using the subcatchment parameters. The nodes receiving runoff are assigned in the subcatchment parameters Dry Weather Flow The following sections describe ways to estimate the average dry-weather flow rates and the temporal patterns of that flow. MSDGC standard practice in the past was to use observed data whenever available and to use simple daily average values. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-24

52 GENERAL MODELING METHODOLOGY However, at the time of the development of these standards, the models are being updated to the most recent set of GIS data and MSDGC is now adding diurnal patterns into the models Estimation from Observed Data Dry-weather flow is estimated from the flow monitoring data. The first step is to identify representative dry weather flow periods when there is minimal RDII influence. Dry weather flow periods are determined by plotting daily average flow and identifying periods when daily flows are stable, with at least 3 days of no preceding rainfall. The daily average flows for these periods can be used as an estimate of the dry weather flow. The next step is to determine the isolated dry weather flow for each flow monitor. The isolated flow is the flow at a flow monitor less the flows already measured by and assigned to any upstream flow monitors. The isolated flow is that flow entering the sewer between the upstream flow monitors and the flow monitor being examined. Dry weather flow values can then be assigned to specific inflow locations. The distribution of the dry weather flow inflow locations should be based on the subcatchment characteristics within the contributing area, such as water supply data, subcatchment area, land use, and tributary sewer characteristics Estimation from Water Supply Data Combining water supply records with GIS data allows for assigning the volume of drinking water supplied to a subcatchment. Using addresses of customers and the associated volume of water used at each address, modelers can use the average volume of water delivered to estimate the dry-weather flow for a subcatchment. The water supply data should be from winter weather months (typically November through February) to eliminate periods of car washing, lawn and garden watering, and swimming pool filling. Additional periods to avoid are major holidays, when possible traveling by consumers would skew water supply demands. The two major uncertainties in this method is the estimation of consumptive use of the drinking water and the long-term infiltration from ground water. If no observed data are available, the modeler should assume that the consumptive use and the infiltration balance. In this case, the water supply data are used without adjustment Estimation from Similar Land Use When observed data and water supply data are not available, the dry weather flow may be estimated from other areas similar to the subject subcatchment. The similar areas should be similar in land use (type and mix of development, density, etc.), age of construction, and similar topography. These factors impact the volume of water supplied, the consumptive use rate, and the expected infiltration rate. Ideally dry weather flow of the similar areas is based on flow monitoring data. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-25

53 GENERAL MODELING METHODOLOGY Estimation from Literature Values When observed data and water supply data are not available, the dry weather flow may be estimated from literature values. One frequently used value is 100 gallons per day per capita (gpdpc) for residential areas. This method is highly uncertain, as the estimation would assume a population for the subcatchment. The modeler should determine commercial and industrial use rates with MSDGC project manager approval Diurnal and Seasonal Patterns Dry weather flows in a sewer vary over time, and it may be important to appropriately model these patterns. The daily change in dry weather flow (a.k.a., the diurnal pattern) can be determined through statistical analysis. The flow measurements should be sorted into time of day groups and the median flow for each time of day calculated. The pattern of the median flows should be smoothed to produce an hourly pattern of daily flows. Each flow pattern should be normalized to the flow meter s daily average dry weather flow to produce a pattern of ratios for hourly dry weather flow to daily average dry weather flow. The hourly patterns of ratios are combined to find a representative pattern. Dry weather flow may also be subject to a seasonal pattern. Using several years of historical data, the median flow for each month should be calculated using the dry periods within each month. Each flow pattern should be normalized to the flow meter s yearly average dry weather flow to produce a pattern of ratios for monthly dry weather flow to yearly average dry weather flow. The monthly patterns of ratios are combined to find a representative pattern. MSDGC standard practice is not to use seasonal patterns for the SWM. The patterns are useful in calibration for specific events so as to properly adjust flows from upstream areas and allow more representative calibration for local areas. For design storms, the patterns may change the results depending on the time of day or year selected for the design event. MSDGC s standard practice regarding diurnal flows is to add the patterns into the model to reflect the most recent set of monitoring data RDII Methodology Modeling RDII is based on the following understanding of the components of RDII. Generally RDII enters the sanitary system via three different paths. First are the short-term inflows, such as stormwater system cross connections and roof leaders connected to the sanitary system. Typically these flows peak in 1 hour or less after peak rainfall. Second is the intermediate infiltration, such as basement sump pumps to the sanitary system and leaking house laterals. These flows peak within a few hours after peak rainfall. Finally, the long-term infiltration enters the sanitary system through leaking mains and manholes. This flow peaks after many hours or even days after peak rainfall. EPA-SWMM allows the use of the RTK method of modeling RDII. The RTK method generates a hydrograph based on precipitation data and catchment area. The MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-26

54 GENERAL MODELING METHODOLOGY total I/I into the sanitary sewer system is determined by combining triangular unit hydrographs from three components of flow: Rapid inflow (short-term fast response) Moderate infiltration (medium-term response) Slow infiltration (long-term slow response) The following three parameters describe the shape and the volume of runoff that enters the sanitary sewer for each triangular unit hydrographs: 5.9 Links R is the fraction of precipitation that becomes inflow or infiltration T is the time to peak of the hydrograph K is the ratio of the recession time to time to peak R can be equated to the area under the unit hydrograph curve and represents I/I volume per unit area as a fraction of precipitation. Total time of runoff is the time to peak and the time of recession (T+T*K). Three available adjustments to the RDII flow are the initial abstraction depth of rainfall, the recovery rate of the storage, and the starting depth of abstraction. The initial abstraction is the total depth of rainfall lost to surface depressions, surface runoff, storage in the soil, etc. This loss decreases the available volume of water for infiltration to the sewer system. Initial abstraction may take several time steps to fill and so delay the onset of infiltration. The rate of recovery of the storage impacts later rainfall time steps and subsequent storms. As time passes, the volume of storage drains and becomes available to intercept later storms. Initial abstraction is used to more accurately model the delay in the start of infiltration and the total volume infiltrated. EPA has provided guidance in developing RTK parameters in Computer Tools for Sanitary Sewer System Capacity Analysis and Planning (EPA/600/R-07/111); U.S.EPA, October MSDGC allows the use of initial abstraction as warranted by the available flow monitoring data. MSDGC allows the use of RTK factors that vary by season as warranted by the available flow monitoring data. For the MSDGC service area, the highest R factors are expected in the spring, with lower values in the summer and fall. Links are the conveyance components of a model that connect a pair of nodes. Links can be categorized into conduits, pumps, orifices, weirs, and outlets Conduits Conduits represent pipes or channels in the model. The cross sectional shape of a conduit can be selected from a variety of defined geometries, both standard and irregular. Additionally, modelers can create their own user-defined closed shapes. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-27

55 GENERAL MODELING METHODOLOGY When modeling open channels, the shape must be deep enough to contain all flows. For modeling open channels that include flood plains, modelers should be careful to not double account for flood plain storage from overlapping cross sections. Energy losses in the hydraulic system are calculated as occurring in the conduit. All losses are calculated based on the velocity of flow, as described below Straight Line Alignment When the upstream and downstream pipes are close in alignment, a small energy loss occurs at each manhole. The loss coefficient varies with the type of benching and the depth of flow through the manhole. MSDGC standard practice is to ignore losses at manholes when the pipes are aligned or close to aligned and to use the pipe roughness to calibrate the depth of flow. The uncertainty in assigning values when the type of benching varies and is usually unknown prevents assigning values to the losses Significant Bends Turbulence caused by significant bends (22.5 degrees or larger) in alignment causes energy losses that should be accounted for in the modeling. Two types of bends are considered in MSDGC standards bends at manholes and bends in alignment. Both losses are assigned at the conduit. For bends at manholes, the losses are assigned to the entrance loss of the outflow pipe using Figure 5-2. For bends in pipe alignment, the losses are assigned to the Other Losses parameter of the conduit Drop manhole Drop manholes occur where the inflowing pipe invert is above the water level in the receiving junction. Inflowing water drops into the junction and creates turbulence in the water at the junction. Velocity energy and gravitational potential energy (change in elevation) are lost in the turbulence of the plunging flow. The assumption of the model is that velocity energy is maintained through a junction unless losses are assigned. A number of equations are necessary to calculate the energy loss from plunging flow. The equations include such factors as depth of water in junction above outflow pipe invert, area of junction, and height of inflowing pipe invert. The complexity of these equations is beyond the capacity of the EPA-SWMM model to calculate. MSDGC standard practice is to assign an entrance loss of 1.0 to the outflowing pipe if the invert of the inflowing pipe is above the crown of the outflowing pipe. Adding an exit loss to the inflowing pipe would cause an incorrect increase in the grade lines of the inflowing pipe. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-28

56 GENERAL MODELING METHODOLOGY Figure 5-2 Losses at Bends Source: Urban Drainage and Flood Control District, (2002), Drainage Criteria Manual Volume 1, Denver, CO MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-29

57 GENERAL MODELING METHODOLOGY Pumps Four different types of pump curves are available in SWMM. These pump curves relate the volume, depth, or head conditions at the inlet node. A fifth option, an ideal transfer pump, allows the flow rate in the pump to equal the inflow rate at its inflow node. MSDGC standard practice is to use the most realistic pump for the situation. The intention is to force development of pump curves to provide realistic estimates and to have pump curves for later improvement. Use of the Ideal pump or overly simplistic pump curves would reduce peak flows downstream, and reduce storage requirements and backwater effects upstream. Therefore, MSDGC does not use the Ideal pump curve. MSDGC standard practice is to model the pump wet well as a storage node. Whenever possible, the pump in the model represents only the actual pump. The downstream pipe should be modeled as gravity conduit or force main as appropriate Orifices Orifices are used to model outlet and diversion structures, such as openings in the wall of a manhole, storage facility, or control gate. The modeled orifice should be as close to the size and shape of the actual orifice as possible. For underflow pipes that are side orifices to a larger pipe, the orifice size is based on the size of the underflow pipe. MSDGC standard practice is to use an orifice coefficient of 0.65 as the initial value. The coefficient may be adjusted during calibration to observed data Weirs Weirs are used to model outlet and diversion structures. SWMM has four different types of weirs: transverse, side flow, V-notch, and trapezoidal. Each uses different formulas to calculate flow as a function of area, discharge coefficient, and head difference across the weir. MSDGC standard practice for sharp crested weirs, such as CSO dams, is to use a weir coefficient of For inflatable dams, the weir coefficient is assumed to be 2.5 as an initial value. If flow monitoring data are available, inflatable dam weir coefficients should be adjusted during calibration to observed data Outlets Outlets are links that are usually used to control outflows from storage units but can be used with other junctions. The outlet flow is based on the head difference between the upstream and downstream nodes. Outlets may be used to model the gravity drainage from storage nodes. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 5-30

58 MODELING SPECIFIC SITUATIONS 6. MODELING TECHNIQUES FOR SPECIFIC SITUATIONS 6.1 Standards for Modeling Specific Situations This document contains both guidelines and standards. Guidelines give the modeler a reference to aid in decision making. Standards are the values and methods expected by MSDGC and should be followed unless satisfactory justification can be provided by the documentation. Both the standards listed here and the available guidelines are discussed in the following text. In the Modeling Specific Situations section, Table 6-1 contains standards that should be followed. Table 6-1 Table of Standards for Modeling Specific Situations Topic Model Option Standard Manholes or other Nearest manhole name with nodes sequential letter appended Conduits Upstream node, dash, downstream node Naming Pumps, Weirs, etc. Location upstream node, dash, downstream node Subcatchment Based on name of first catchment downstream High Rate Treatment Sludge Return Fraction of treated flow returned to interceptor Pumps & Force Force Main modeling Model force main rather than extend pump link Mains Force Main modeling Use circular gravity conduit with appropriate manholes Flap Gate Flap Gate use Only where flap gate exists or is proposed Sewer Lining Change in pipe diameter Adjust diameter to account for thickness of liner Existing RDII stays in combined sewer Adding new storm Minimum runoff from 5% sewer Sewer Separation of original area stays in combined sewer Splitting surface Total area maintained, add catchments stormwater conveyance 6.2 Naming Conventions When adding a node not previously in the SWM, modelers should always try to retrieve the manhole number from GIS or from as-built drawings. When the manhole MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-1

59 MODELING SPECIFIC SITUATIONS number is not available, modelers should use the nearest manhole number, adding the letter A to the end. If the name is already taken, use the letter C, D, E, etc. until there is a unique manhole ID. Do not use the letter B when creating a unique node name; the letter B is reserved to identify blind manholes. The naming conventions for conduits should contain both the upstream and downstream node names. For example, the upstream node of link is , and the downstream node is The naming conventions for an orifice, weir, and pump are similar to a conduit except that orifices, weirs, and pumps are also numbered. When adding a new orifice, pump, or weir, the name should contain the link type, the location identifier, symbol, and the names of the upstream and downstream nodes (e.g., PUMP7@ ). The location identifier should be the name of the location (such as Boldface), but a unique number may be used. When existing subcatchments are subdivided, the subsequent subcatchments will be named from the original catchment name. The MSDGC standard method is to add a letter A, B, etc. to the end of the original subcatchment name. For new subcatchments, the name will be based on the name for the first subcatchment connecting to the sewer downstream of the new subcatchment. Generally SWM subcatchment names end in a four-digit number, such as LMC002C0114. The new subcatchment name will use the same characters to the left of the four digits plus a new four-digit number. The first of the four digits will be increased by one (1) and the other three digits set to zero (0). Subsequent new subcatchments will be number sequentially moving upstream. Using the example name, the first new subcatchment would be LMC002C1000, followed by LMC002C1001, LMC002C1002, LMC002C1003, etc. 6.3 Review Impacts Changes to model parameters may impact the flows and water levels beyond the immediate area of the changes. The expected impacts include decreased overflows upstream of the model change from increased conveyance capacity. An unexpected impact could be increased conveyance raising downstream interceptor levels, causing in turn an RTC facility to reduce underflow volumes, which then cause larger overflows at the RTC facility. Another unexpected impact could be the elimination of an overflowing manhole because of improved model stability resulting from the changes in model parameters. Following the changing of the SWM for a project, whether adjustments for modeling the project or updating of the existing parameters, the modeler should review the results for impacts outside the project area Upstream Backwater Impacts The changes to the SWM may cause increased water levels upstream of the model changes. Model results will be reviewed for impacts on: Peak flows and water surfaces; Regulator and RTC operations; MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-2

60 MODELING SPECIFIC SITUATIONS Pump station operation; and, Possible basement and manhole flooding Pipe Capacity & Flooding Manholes Projects (model changes) that increase either the flow (peak flow or total volume) or water level must be reviewed for downstream impacts. Projects that locally increase peak flow without sufficient downstream capacity are of special concern. An example of this situation would be the replacement of a 12-inch-diameter sanitary sewer with an 18-inch-diameter sanitary sewer for improving capacity. Downstream pipes must be reviewed to see if the now less-attenuated peak flow causes manhole flooding, basement flooding, or other undesired impacts. These impacts must be mitigated as part of the project. For projects to be built in phases, the impacts of each phase must be tested Downstream CSO Volumes One of the primary purposes of the SWM is to model CSO flows. Changes to the SWM for updating parameters and for project modeling may impact the flows and volumes at CSOs. As small changes to the model may not show a significant impact for a design storm, the CSO volumes should be compared using the 1970 Typical Year rainfall. Small changes may accumulate to significant changes during the year or back to back storms may interact. For projects that change the flows (peak flows or total volume) to the CSO regulator, the impacts on CSO overflow volumes should be noted and documented. 6.4 High Rate Treatment Systems High Rate Treatment (HRT) systems are intended to remove solids and disinfect wet weather flows that would otherwise overflow untreated to the receiving streams. The HRT described in this section is an approximation and can be modeled in greater detail. HRTs generate sludge that must either be stored on site for later disposal or returned to the interceptor for transport to the WWTP. The selection 95% of HRT capacity to discharge and 5% to sludge return to interceptor is a guideline that may vary with the specifics of the HRT being modeled Level of Detail in Modeling High Rate Treatment facilities are complex facilities that are simplified for modeling in EPA-SWMM. HRTs are modeled as a system of pumps and storage nodes. Figure 6-1 shows an example of an HRT set-up in SWMM. Note that the figure and text are an example, and the HRT should be modeled as close to the proposed design as practical. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-3

61 MODELING SPECIFIC SITUATIONS In this case, an HRT was modeled as an alternative at an existing CSO. A storage unit should be placed between the regulator and the overflow. Once flow enters the storage facility, it can be pumped by the HRT or the sludge pump, or it can overflow. Figure 6-1 Typical HRT Set-up Storage The volume of the storage unit should only be the storage inherent in the holding tanks. When a defined storage volume is not available, the modeler should use engineering judgment to determine an appropriate storage volume. The volume of the HRT storage is the storage in the node below peak elevation observed in the storage node. Initially, the offset of the overflow pipe and the node invert elevation should be set so that the volume in the HRT storage node below the overflow pipe is the storage estimated for the HRT facility. The offset and node invert should be adjusted so the design storm storage at peak water surface elevation is the estimated HRT storage volume. Careful attention must be paid to ensure that the storage unit does not flood during the operation of the HRT HRT Pumping The pumps in the model for an HRT are sized to test the impacts of the HRT on the SWM. The HRT pump should first be sized according to the design storm defined for the particular project. The HRT pump curve should initially vary linearly by depth in the storage unit, operating up to 95% of the total HRT capacity at the elevation where flow begins to leave out the overflow. The flow being pumped by the HRT pump is assumed to receive primary treatment and is pumped to an outfall (i.e., a receiving stream). For wet weather events in excess of the capacity of the HRT, excess volume will overflow from the storage node and be counted as MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-4

62 MODELING SPECIFIC SITUATIONS overflow volume. The HRT pump will initially be set to turn on when any water enters the storage node. The 95% treatment and the 5% sludge return rates are assumptions for the example model HRT. Specific fractions of the HRT design capacity should be determined for each HRT being modeled Sludge Return to Interceptor The sludge pump shown in Figure 6-1 pumps 5% of the HRT capacity back to the underflow where it can reach the treatment plant and receive full treatment. As the sludge generation generally is proportional to the total HRT treatment rate, the sludge pump curve must mirror the shape of the HRT pump. The 95% treatment and the 5% sludge return rates are assumptions for the example model HRT. Specific fractions of the HRT design capacity should be determined for each HRT being modeled. The interceptor in the vicinity of the return sludge discharge point must be reviewed for excessive surcharge or overflows because of the additional flow. Solutions to excessive surcharge include gating the underflow pipe to reduce flows to the interceptor, changing to the HRT to reduce the sludge return rate, or using sludge storage at the HRT Possible Variations One possible variation to more accurately represent the operation of the HRT is to include the possible use of the HRT as a storage facility. In this case, the HRT and sludge pumps turn on when the volume in the HRT storage node reaches the volume in the HRT tanks. For this variation, a third pump to drain the HRT storage node after small events must be used to empty the storage when the HRT is not triggered. The drain pump will discharge to the interceptor. A second variation would be to step the HRT and sludge pump curves to account for the activation of HRT treatment trains. The HRT pump and sludge pump rates must add to the total HRT capacity at each point in the capacity curve. 6.5 Control Rules Control Rules are used to adjust links, pumps, weirs, and regulators in a conveyance system during a simulation. Control Rules allow the adjustment of model parameters in reaction to modeled or time series values. Examples include: Adjusting gates to control water levels upstream or downstream of the gate Limiting flow through a pipe to control downstream flows Turning pumps on or off separate from the pump curve settings Control rule operation can be reviewed using the Options Menu, General tab by turning on the Report Control Actions under Miscellaneous. Be aware that all control actions by all control rules will be reported in the Report file. When testing a new or modified rule, the recommended method is to use only a portion of the model with MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-5

63 MODELING SPECIFIC SITUATIONS boundary condition time series as needed. Artificial time series with extreme values may be used to verify the proper response for the full range of possible values. A Control Rule is a statement comprised of a label, condition clause, action clause, and a priority value that are edited in the Control Rules Editor. An example of a Control Rule: RULE ORIFICE67A IF NODE B DEPTH > 1.1 THEN ORIFICE ORIFICE67@ A setting = 0 PRIORITY 1 Table 6-2 from the EPA SWMM Help Menu shows the objects and attributes that can appear in a Control Rule. Table 6-2 Control Rule Attributes Node Link Pump Object Attributes Value DEPTH Numerical value HEAD Numerical value FLOW Numerical value FLOW Numerical value DEPTH STATUS SETTING FLOW Numerical value ON or OFF Pump curve multiplier Numerical value Orifice SETTING Fraction open Weir Outlet SETTING Rating curve multiplier Simulation TIME DATE CLOCKTIME Elapsed time in decimal hours or hr:min:sec Month/day/year Time of day in hr:min:sec Condition Clause The condition clause has the following format: object, ID, attribute, relation, and value. The object parameter refers to the category of an object (node, link, etc.). The ID is the object s ID label. The attribute parameter is an attribute or property of the referenced object. The relation parameter is a relational operator (=,<>,<,<=,>,>=). The value parameter is a specified value of the referenced attribute. As can be seen in the Control Rule example, the condition clause identifies that Node B must have a depth greater than 1.1 for the action to occur Action Clause The action clause can have two different formats, depending on if it is referencing the status of a pump or the setting of a regulator. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-6

64 MODELING SPECIFIC SITUATIONS When referencing the status of a pump, the action clause has the following format: pump, ID, and status (ON/OFF). When referencing the setting of a regulator, the action clause has the following format: object (pump/orifice/weir/outlet), ID, and setting. As can be seen in the Control Rule example above, when the condition clause is met, ORIFICE67@ A will be fully closed Priority Value When there are multiple rules that require conflicting actions on the same object, a priority value is used to determine which rule applies. The higher the priority number, the more important the rule. Priority ranges from 5 as the most important to 1 as least important. A rule without a priority value is given lower priority than one with a value. Additionally, if two rules have the same priority value, the rule that appears first is given the higher priority Control Curves The Control Curve determines how the control setting of a pump or flow regulator varies as a function of some control variable, such as depth or flow. A Control Curve can be used in applications where continuous control in a simulation is required. The Control Curve is created in the Curve Editor and referenced in an action clause as the setting parameter. The range of values in the control curve should extend above and below any possible modeled input values. The modeler must understand the impacts of extreme values on the controlled value. For example, when controlling for the gate opening (actually fraction of full open flow) based on the depth in a manhole, the range of depth must go from zero feet to the full depth of the manhole. This range of depths allows the modeler to know the gate settings for unexpected events including model instability Control Rule Examples The use of Control Curves is highlighted by two examples. The first example is Rules ORIFICE67A and ORIFICE67B. As the two rules have the same priority, ORIFICE67A will be used in case of both IF statements being true since it is first in the list. Assume that node B is a manhole on a sewer line with dry weather flow as well as wet weather flow. Assume that dry weather flow is below 0.3 feet deep and the wet weather peak is above 1.1 feet. Before and during a wet weather event occurring, the orifice is fully open and stays open until the depth exceeds 1.1 feet. At 1.1-foot depth, the orifice fully closes and stays closed until the depth drops to 0.3 feet. RULE ORIFICE67A IF NODE B DEPTH > 1.1 THEN ORIFICE ORIFICE67@ A setting = 0 PRIORITY 1 MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-7

65 MODELING SPECIFIC SITUATIONS RULE ORIFICE67B IF NODE B DEPTH < 0.3 THEN ORIFICE setting = 1.0 PRIORITY 1 The above rules can cause instabilities if the target node B is downstream of the controlled orifice. Closing the orifice when the depth in the node reaches 1.1 feet could then allow the depth to drop to 0.3 feet. At this depth, the gate fully opens and the depth increases. Depending on the size of the gate, the distance to the target node, and the time for the orifice to open and close, the orifice setting could change between the two extremes at each routing time step. Another problem occurs if the target node is upstream of the orifice. When the depth in the node reaches 1.1 feet, the orifice closes. Once closed, the orifice keeps the upstream node above 1.1 feet and so never opens. The alternative rule below uses a control curve to modulate the orifice setting. RULE ORIFICE67C IF NODE B DEPTH > 0.01 THEN ORIFICE ORIFICE67@ A setting = CURVE 67 PRIORITY 1 Curve 67 Controller Value Control Setting The controller value is the depth at node B and the control setting is the multiplier for the orifice capacity. In this case, the orifice proportionally changes from fully open to fully closed as the depth rises from 0.3 feet to 1.1 feet. If the shape of the control setting transition is a curve rather than a straight line, additional points can be added between 0.3 feet and 1.1 feet as needed Real Time Control RTC features have been implemented in recent projects completed by MSDGC. RTC facilities (as the term is used within MSDGC) are designed to optimize the amount of combined sewage reaching the treatment plant while minimizing the overflows from the CSO regulators; this is accomplished by storing wet weather flows until the interceptor has capacity. Each RTC site makes use of in-line storage for the wet weather flows. This practice is consistent with maximizing the inherent storage in the collection system and maximizing flow to the WWTP as outlined in MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-8

66 MODELING SPECIFIC SITUATIONS EPA s Combined Sewer Overflows: Guidance for Nine Minimum Controls May Using level sensors, water levels at several locations are monitored on a constant basis. When levels reach a programmed target point, a predetermined action occurs, such as a sluice gate opening/closing or an inflatable dam increasing/ decreasing its internal pressure. The RTC response to specific levels can come as one of three types: Full, Direct, and Proportional Integral Derivative (PID). Other systems using sensors and control systems to adjust sewer system operation in real time may be used by MSDGC but will be named using other terms Full Real Time Control The Full Real Time Control method is a basic method for simulating RTC that utilizes Control Rules to regulate flow by completely opening or closing gates when triggered Direct Real Time Control The Direct Real Time Control method references a Control Curve to apply a continuous degree of control to a pump or flow regulator as a function of a control variable, such as depth, flow, or time. Observed data or known operational strategies of an RTC, such as an inflatable dam or sluice gate, are used to create a Control Curve. This Control Curve is referenced in a Control Rule to simulate the RTC function Proportional Integral Derivatives A PID is a generic, closed-loop control scheme that tries to maintain a desired setpoint on some process variable by computing and applying a corrective action that adjusts the process accordingly. A PID controller calculates the difference between a measured process variable and a desired setpoint, and attempts to minimize the difference by adjusting the process control inputs. RTCs can be modeled using PIDs to control weirs, orifices, and pumps based on a specified depth in a manhole or flow in a pipe. EPA SWMM uses the following classical PID controller equation: The specified values in a PID are the factor of proportionality (Kp), the integration time (Ti), and the derivation time (Td). Though the Ti and Td values are generally determined through an iterative calibration process, the starting value of Kp will either be 1 or -1 depending on whether the control action is direct or reverse. A direct control action is where an increase in the link setting causes an increase in the controlled variable. A control action, such as adjusting an orifice to maintain a desired flow downstream, would be a direct action; here the Kp value would be positive. However, controlling an orifice to maintain an upstream water level would be a reverse control action, and the Kp would be negative. Figure 6-2 shows typical starting values for the three PID values from DHI Mouse RTC User Guide. DHI Mouse software uses the same controller equation for PIDs as MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-9

67 MODELING SPECIFIC SITUATIONS EPA SWMM and therefore these values represent common PID controls used for RTC features. Figure 6-2 Typical Starting Parameters for PID Values Source: DHI, Mouse RTC User Guide, 2004 Once the starting point values are in place, modelers may use desired set points or observed data to optimize the timing and shape of the hydrographs produced by the RTC facilities. Based on the PID algorithm, general guidelines for the desired shape of the RTC are presented in the Mouse RTC User Guide from DHI. Suggestions on which PID parameter to change are given based on the shape of the simulated RTC hydrographs. Figure 6-3Error! Reference source not found., Figure 6-4Error! Reference source not found., and Figure 6-5Error! Reference source not found. are examples of how the hydrograph curves may respond to the set-point chosen for either a flow or water level based on the choice of PID constant used. 6.6 Pumps and Force Mains Pumps and force mains are the two links in SWMM intended to operate under pressure flow conditions. The other closed conduit shapes are capable of being modeled under pressure flow conditions using the Manning s n friction method. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-10

68 MODELING SPECIFIC SITUATIONS Figure 6-3 Variability Around Set Point based on Proportionality Factor, K Source: DHI, Mouse RTC User Guide, 2004 Figure 6-4 Variability Around Set Point based on Derivation Time, T D Source: DHI, Mouse RTC User Guide, 2004 MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-11

69 MODELING SPECIFIC SITUATIONS Figure 6-5 Variability Around Set Point based on Integration Time, T I Source: DHI, Mouse RTC User Guide, Pump Pumps may be used as a combination of pump and force main to convey flow from one point to a distant point. This use of a pump link allows the modeler to delay developing the details of pipe sizing, layout, etc. until later in the project. MSDGC standard practice is to include the force mains and downstream gravity sewers at the modeler s best estimate of detail, as shown in Figure 6-6. Figure 6-6 Pump Modeling Force Main A force main is a circular conduit that uses either the Hazen-Williams or the Darcy- Weisbach method of calculating friction losses. The method used is selected globally for the SWM in the Options window under the Dynamic Wave tab. The advantage to using the Force Main conduit instead of another pipe shape is the ability to use either of the friction methods and the ability to have multiple barrels. MSDGC standard practice is to model force mains using the Circular conduit shape rather than the Force Main. Modelers may use Force Main if the upstream network MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-12

70 MODELING SPECIFIC SITUATIONS was sized using either of the Force Main friction methods or if the node depth is not sufficient to prevent node flooding from the pressurized flow. 6.7 Flap Gates Flap gates are an effective tool to preventing backflow problems experienced during a SWM simulation. Flap gates can only be added to conduits, orifices, weirs, and outlets by selecting YES from the flap gate drop-down menu of the attribute window. When adding a flap gate, modelers should verify that preventing backflow and possible relief from a surcharged interceptor is not having a negative impact elsewhere in the system. For example, adding a flap gate to the underflow pipe of a low elevation CSO connected to a surcharging interceptor would prevent the interceptor flows from flowing back up the underflow pipe. Without the relief at the CSO, the interceptor HGL would rise and cause increased overflows at other CSOs; new or increased manhole overflows; and possibly increased peak flows in the interceptor downstream. Flap gates should be used only where a flap gate actually exists or is proposed. Use of a flap gate for model stability is not acceptable if the flap gate impacts backflows that may occur from normal model results. Other stability techniques are preferred, such as adding small storage nodes, adding surface ponding, using smaller routing time steps, or shorter conduit lengthening. 6.8 Storage Tanks Storage tanks in SWMM can be of two types: a functional curve or a tabular curve. A functional curve calculates the cross sectional area of the storage tank based on the following equation: Area = A* Depth B + C where the depth is expressed in feet and the area expressed in square feet. When the cross sectional area of a storage tank is known and the storage node is vertical sided, the modeler should assign the cross sectional area to the coefficient A (in square feet) and assign 0 to the coefficients B and C. The functional curve is most effective when modeling a storage tank. Tabular curves are useful when modeling a detention basin where the cross sectional area varies with depth. The tabular curve is set up as a stage storage curve where the user can specify the cross sectional area at different depths in the storage unit. The type of curve being used should be properly selected from the shape curve drop-down menu in the storage unit window. 6.9 Tunnels Tunnels are modeled as conduits, but modeler should pay attention to model stability, acceptable surcharge, realistic gate operations, and realistic depth of tunnel. EPA SWMM does not fully model transients in tunnels. Other specialized software should be used for detailed modeling of tunnel operations. EPA SWMM should be used for modeling the general operation of the tunnel in coordination with the rest of the SWM. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-13

71 MODELING SPECIFIC SITUATIONS Tunnels normally have junctions at large distances (approximately 1,000s of feet). These large distances may lead to instabilities during model runs. The addition of intermediary junctions or the use of small time steps may be needed for model stability. Determining and maintaining an acceptable surcharge involves considering the structural stability of the tunnel and the impacts of high water on other structures. Large fluctuations in pressure may damage the tunnel liner, dropshaft walls, and other structures. Generally tunnel liners can tolerate very high water velocities but the closed nature of tunnels can cause water hammers and other transients of concern. Modelers should develop acceptable surcharges and velocities in consultation with tunnel design and construction experts. Modelers should review surcharge sufficient to cause backwater in connection conveyances for impacts upstream Regulators and CSO Structures Regulators are used in certain CSOs in the MSDGC system to limit the flow to the interceptor. These regulators consist of two types: single chamber and dual chamber Single Chamber Regulator Single chamber regulators limit flow to the interceptor based on the water level in a chamber at the upstream end of the underflow pipe. As the water level in the chamber raises, a float and gate system activates to throttle down flow from the underflow to the interceptor. Single chamber regulators allow water to enter the interceptor but at a controlled rate to minimize the peak flow to the interceptor. In EPA SWMM, a single chamber regulator should be set up as follows: Inflow To storage node at regulator to account for vault volume Overflow Outfall with weir as appropriate Underflow o An orifice, usually side, to the gate chamber o A storage node for gate chamber o A side orifice as connection to the interceptor All the sizes of the storage units and orifices should be sized according to as built drawings or according to GIS. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-14

72 MODELING SPECIFIC SITUATIONS Figure 6-7 shows a schematic for a single chamber regulator. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-15

73 MODELING SPECIFIC SITUATIONS Figure 6-7 Schematic of Single Chamber Regulator Dual Chamber Regulator Dual chamber regulators restrict flow to the interceptor based on the water level in a chamber connected to the CSO. As the water level in the CSO rises and raises the water level in the control chamber, a float and gate system operates to restrict flow from the underflow to the interceptor to ensure the interceptor is maintaining capacity. Dual chamber regulators limit the amount of stress on the interceptor, but this happens at the cost of allowing more overflow than in the single chamber regulator. In EPA SWMM, a dual chamber regulator should be set up as: Inflow To storage node at regulator to account for vault volume Float Chamber o A side orifice for water to flow to and from the float chamber o A storage node for the float chamber Overflow o A weir to pool DWF for underflow orifice o A storage node between the two weirs o A weir to form a pool of overflowing water for diversion to the flow chamber o A small conduit routed in parallel to the weir for draining the float chamber after the end of an overflow event. The actual method used is a notch in the downstream weir. o An outfall Underflow A gated side orifice as a connection to the interceptor Storage units and orifices should be sized according to as-built drawings or according to GIS. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-16

74 MODELING SPECIFIC SITUATIONS Figure 6-8 shows a schematic for a dual chamber regulator. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-17

75 MODELING SPECIFIC SITUATIONS Figure 6-8 Schematic of Dual Chamber Regulator Control Curve Both single and dual chamber regulators utilize Control Rules and Control Curves to restrict underflow. The control rule for single chamber regulators should operate the underflow orifice immediately downstream of the regulator according to target values for the depth of the storage unit on the underflow immediately downstream of the regulator. The control rule for double chamber regulators should operate the underflow orifice immediately downstream of the regulator according to target values for the depth of the storage unit on the overflow immediately downstream of the regulator. The target values for the control curve should be provided in as-built drawings Non-Circular Sewers Although circular is the most common shape in MSDGC s collection system (as well as the default in EPA SWMM), EPA SWMM offers several different shapes, including circular, rectangular, trapezoidal, and triangular among many others. The user can also define a custom shape or an irregular shape. Figure 6-9 shows available uncommon pipe shapes, while Figure 6-10 overlays the shapes on a single image to aid in matching existing pipes to EPA SWMM model pipe shapes Pipe Shapes The horizontal ellipse pipe shape can be used where the available height is limited because of shallow depths or location of other infrastructure. The vertical ellipse pipe is used where width is limited but height is not, or where minimum velocities must be increased. The arch shape is a precast shape used where strength is needed, as the cover is minimal. The arch top provides strength to support loads, while the wide base provides larger flow areas than an equivalent-height circular pipe. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-18

76 MODELING SPECIFIC SITUATIONS Figure 6-9 EPA SWMM Standard Pipe Shapes Gothic Shape Baskethandle Shape Egg Shape Catenary Shape Semi Circular Shape Arch Shape MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-19

77 MODELING SPECIFIC SITUATIONS Figure 6-9 EPA-SWMM Standard Pipe Shapes, continued Semi-Elliptical Shape Horseshoe Shape Horizontal Ellipse Shape Vertical Ellipse Shape Custom Link A custom shape requires a user-defined shape curve in the following format: Depth/Full Depth and Width/Full Depth. Values in the custom shape curve are proportional and should vary between zero and one. Custom shapes are helpful for older pipes in the MSDGC collection system. Another user-defined shape that is helpful for modeling open channels is an irregular shape. An irregular channel should be defined using the transect editor, where the user can define the shape using the station and elevation, as well as being able to define the bank stations and roughness of each side of the bank. The irregular channel should only be used where survey data are available. The modeler should document the survey results and provided them to MSDGC for review. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-20

78 MODELING SPECIFIC SITUATIONS Figure 6-10 EPA-SWMM Pipe Shape Comparison BASKET HANDLE SEMI-ELLIPTICAL SEMI-CIRCULAR ARCH CATENARY 6.12 Lining of Sewers Sewer lining is an effective way to prevent leaks in old pipes and/or increase the velocity through a rough section of pipe. Where sewer lining is reported, the user must change the pipe roughness to a value consistent with the lining material. MSDGC standard procedure is to adjust the pipe diameter to account for the thickness of the liner Low Impact Development EPA SWMM and later versions have controls built into the software to model such LID structures as bio-retention cells and vegetative swales. These controls are modeled as changes to the hydrology of the subcatchments, though they include hydraulic structures. LID structures have impacts beyond the attenuation of peak flows and removal of water from the sewer systems. LID changes the water quality (nutrients, temperature, dissolved oxygen, sediment, etc.) leaving a subcatchment. Water quality modeling, however, is beyond the scope of this document. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-21

79 MODELING SPECIFIC SITUATIONS Modeling Parameters The parameters used in modeling hydrology and hydraulics are known to varying degrees of certainty. For example, pipe is constructed in a limited range of sizes so that a pipe is 36 inches or 42 inches in diameter; it is unlikely to be 38.5 inches. In contrast, the maximum infiltration rate of a soil surface depends on its material makeup (sand, silt, clay, organics), its history (undisturbed, construction compacted, dumped fill), the depth to bedrock, and other factors. The modeler should use judgment in determining which parameters can be changed and how much to change them. Whenever possible, site data should be used over literature values Porosity and Storage Volume For LID techniques that involve placing soil and fill, the available storage volume in the soil has an impact on the model results. The available storage volume varies according to how much water is in the soil pores. Within a given volume of soil or fill, the particles of the material occupy a portion of the volume. The remaining volume of air and water (a.k.a., the pore space) is given by the porosity of the material (the volume of the pore space within a unit volume of the soil). The porosity assumes no water is adhering to the soil particles. In reality, some water remains in the soil. Two common measures of the volume of water remaining in the soil are used: wilting point and field capacity. Wilting point describes the water layer that adheres to the soil that can be removed by evaporation but not by plant transpiration (hence, the moisture level where plants wilt). Field capacity is the measure of the water that can be removed by evapotranspiration but not by gravity. As shown in Table 6-3, the porosity of various soil textures is approximately the same. However, as the soil texture becomes finer, the pore sizes and soil particles become smaller. These two changes lead to water trapped in small pores (capillary effect) and adhering to particles. The result is that the fraction of pore space available for water storage (water that can be drained by gravity and evapotranspiration) is reduced as shown in the last column. For gravels, the field capacity and wilting point are small compared to the uncertainty in porosity and are considered negligible for this document Infiltration Parameters EPA SWMM requires that only one infiltration method be used for the entire model. Currently the SWM uses the Horton method for calculating infiltration. More information on infiltration parameters is found in Section MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-22

80 MODELING SPECIFIC SITUATIONS Table 6-3 Soil Classification and Porosity Fraction of Total Volume Porosity Less Soil Texture Field Field Class Porosity Wilting Point Capacity Capacity Sand Loamy Sand Sandy Loam Loam Silt Loam Sandy Clay Loam Clay Loam Silty Clay Loam Sandy Clay Silty Clay Clay Source: Rawls, W.J. et al., (1983). J. Hyd. Engr., 109:1316. (from EPA-SWMM Manual) LID Controls Modeling Using the SWMM engine , modelers have the option to explicitly simulate five different LID controls. The LID controls can be added into models to replicate field conditions that reduce the amount of runoff within a watershed by the combination of infiltration, detention, and evapotranspiration. LIDs are represented by areas containing vertical layers. Depending on the LID, the layers include surface, pavement, soil, and storage, with the underdrain as a separate option. LID controls are added to the model by first assigning layer properties to the needed types of LID using the LID Control Editor under the Hydrology tab. Each set of LID properties is saved under a unique control name. The control name refers to one set of layers without regard to the area of the LID footprint. For example, if every rain garden has a standard underdrain pipe, depth of amended soil layer, etc. regardless of rain garden size, all rain gardens are modeled using the same control name. Two concepts of modeling LID controls can be used; within the subcatchment and as the subcatchment. Within the subcatchment, a designated percentage of the impervious area of the flows into the LID control(s). For LID controls within the subcatchment, multiple controls can be used as long as the total area flowing to the controls sums to the subcatchment impervious area or less. The percentage of the impervious area for each named control is set for that control. The underdrain(s) and the overflow(s) are routed to the outlet assigned for the subcatchment. If the LID control takes the full area of the subcatchment, the subcatchment and the LID control MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-23

81 MODELING SPECIFIC SITUATIONS can receive runon flow from upstream subcatchments while the underdrain and overflow can be assigned as flowing to another subcatchment. For each subcatchment, the LIDs are assigned and additional details added in the Subcatchment editor of the Hydrology tab LID Control Editor LID Controls must be described on a unit area basis before addition to the subcatchments. The available LID controls are: Bio-retention Cells (rain gardens) Infiltration Trench Vegetative Swale (trapezoidal channel only, no storage) Porous Pavement (continuous concrete or asphalt, modular systems, and pavers) Rain Barrels Table 6-4 lists the layer combination that makes up each LID control. Table 6-4 LID Control Layers LID Type Surface Pavement Storage Soil Underdrain Bio-Retention Cell R N R R O Porous Pavement R R R N O Infiltration Trench R N R N O Rain Barrel N N R N R Vegetative Swale R N N N N R = required, O = optional, N = not available EPA SWMM Help Menu, , 2010 The modeler must be aware of the parameters and units used in the LID Controls Editor. For example, depths of layers are in inches or millimeters rather than the feet or meters of other EPA SWMM model parameters. Also, void ratio (volume of voids over volume of soil particles) is used as well as porosity (volume of voids over total volume). Table 6-5 lists the surface layer parameters that make up the top surface of the LID control. The depth surface storage or the depth of the swale cross section is the maximum depth of storage above the top of the soil. For porous pavement and vegetative swale, all inflow volume that exceeds the depth is discharged in that time step. The fraction of vegetative cover reduces the volume of storage from the volume of vegetation. Surface roughness (Manning s n) and surface slope are used in the two controls that involve flow across a surface: porous pavement and vegetative swale. The swale side slope is used only for the vegetative swale. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-24

82 MODELING SPECIFIC SITUATIONS Table 6-5 LID Surface Layer Parameters Storage Vegetative Surface Surface Swale LID Type Depth Cover Roughness Slope Side Slope Bio-Retention Cell R R N N N Porous Pavement R R R R N Infiltration Trench R R N N N Rain Barrel R N N N N Vegetative Swale R R R R R R = required, N = not used EPA SWMM Help Menu, , 2010 The pavement layer is used only for porous pavements. The pavement layer considers only the thickness of the paving system. The bedding layer is modeled in the storage layer tab of the LID Control Editor. The void ratio refers to either the void ratio of the continuous porous asphalt or concrete pavement, the fill within modular units, or the bedding between the pavers. Impervious surface fraction refers to the fraction of the LID control that is impervious, such as driving lanes, paver units, or modular unit frames. The permeability of the porous pavement or fill material can be modeled as clogging because of fine materials. The clogging factor is the number of pore volumes (thickness x void ratio x (1-impervious surface fraction x area)) that will cause the permeability to drop from the initial value to zero because of clogging. The reduction is linear and starts from full permeability at the beginning of the model run. The storage layer is intended to be the gravel layer underlying the porous pavement or the soil layer of the bio-retention cell or infiltration trench. This layer is also used to describe the height (but not the area or volume) of rain barrels. Vegetative swales do not have storage layers. The height parameter and the void ratio describe the storage volume. Conductivity is the maximum flow rate through the storage layer, not the underlying soil. The clogging factor modifies the conductivity similar to the permeability of the pavement layer. The vertical flow through the storage layer and into underlying soil is limited to the lower of the two conductivities. That is, if the flow into the LID control, through the surface soil or pavement, and through the storage layer, is greater than the conductivity of the underlying soil, the soil s lower conductivity will cause storage within the storage layer. The Underdrain System is required for Rain Barrels and optional parameter for Bio- Retention Cells, Porous Pavement, and Infiltration Trenches in the LID Control Editor. The Underdrain System conveys water to a conventional storm drain that has been stored at the bottom of a layer. The Underdrain System consists of the Drain Coefficient, Drain Exponent, and Drain Offset Height. The drain coefficient and exponent determines the rate of flow through the underdrain as a function of stored water above the drain. The drain offset height is the difference in height from the bottom of the storage layer to the underdrain pipe invert. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-25

83 MODELING SPECIFIC SITUATIONS As the LID Control Editor describes the unit area of a LID, the drainage rate is volumetric flow rate per unit area (in/hr or mm/hr). The soil layer describes the amended soil for bio-retention cells. The flow calculations use the EPA SWMM Aquifer method. The porosity is the fraction of the soil volume that is voids. The field capacity is the fraction of the soil volume that is water that is held in place by surface tension and does not drain by gravity. The wilting point is the fraction of the soil volume that is water held to soil particles too tightly for plant roots to take up. By definition, porosity is greater than field capacity, and both are greater than the wilting point. The suction head is the average soil capillary suction along the wetting front. Table 6-6 shows hydraulic conductivity, suction head, porosity, field capacity, and wilting point for various soil classifications. Table 6-6 Characteristics of Various Soils Soil Texture Class Ksat FC WP Sand Loamy Sand Sandy Loam Loam Silt Loam Sandy Clay Loam Clay Loam Silty Clay Loam Sandy Clay Silty Clay Clay Ksat = saturated hydraulic conductivity, in/hr = suction head, in. = porosity, fraction FC = field capacity, fraction WP= wilting point, fraction Source: Rawls, W.J. et al., (1983). J. Hyd. Engr., 109:1316. The conductivity slope measures the rate at which a soil s hydraulic conductivity decreases with decreasing moisture content. SWMM uses the following equation to express this relationship: K=Ksat*exp(-HCO*(porosity-moisture content)) Ksat is the saturated conductivity and HCO is the conductivity slope. The partly saturated K value is used to predict the rate at which infiltrated water moves through a layer of unsaturated soil when modeling groundwater or LID controls. HCO can be estimated as the slope of a best fit line through a plot of Log(K) versus moisture content. The next version of the EPA SWMM Manual will address this software detail more thoroughly. Table 6-7 shows typical values for different soil types. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-26

84 MODELING SPECIFIC SITUATIONS Table 6-7 HCO by Soil Type Soil Type HCO Sand 5 Loamy Sand 5.7 Sandy Loam 7.5 Loam 10.6 Silt Loam 10.8 Sandy Clay Loam 6.8 Clay Loam 10.1 Silty Clay Loam 12.8 Sandy Clay 9 Silty Clay 14.5 Clay LID Within Subcatchments For each subcatchment, a number of LID Controls can be added provided the impervious area treated is 100% or less of the subcatchment impervious area. Each named LID Control can be added to the subcatchment as a number of identical controls. Identical in this case means that each line in the table of controls assigned to the subcatchment refers to controls that: Have the same layers as described by the control name in the LID Control menu Have identical footprints Receive flow from the same sized areas of the impervious area Have identical width of surface flow (porous pavement and vegetative swale) Have identical initial saturation (soil layer for Bio-Retention Cells, storage layer for others) Do or do not flow onto pervious areas If the controls differ in any of the listed factors, additional lines of controls are added to the subcatchment s table of controls. The modeler must verify that all the LID Controls combined treat 100% or less of the impervious area LID as Subcatchments The modeler may want to use a LID Control as the entire subcatchment when modeling a green roof or regional water quality basin. In the case of a green roof, the runoff characteristics are very different from the rest of the subcatchment, so the situation is better represented as a new subcatchment. For the regional water quality basin, the basin can accept the runoff from several subcatchments as runon. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-27

85 MODELING SPECIFIC SITUATIONS Sewer Separation Separating the stormwater from the combined sewer is likely to be a major part of the MSDGC sustainable infrastructure effort. Two general types of separation are possible for combined sewer systems new stormwater system or new sanitary system. Of the two types, new stormwater systems will be assumed for the MSDGC service area. New stormwater systems encourage the development of sustainable infrastructure to reduce the size of the stormwater conveyance, allow infiltration, and allow water quality improvements. Installing new sanitary systems means that the stormwater remains in the existing pipes with limited opportunities for sustainable infrastructure improvements. One major concern with converting the combined system to stormwater is the likelihood that some sanitary connections may remain. If the project uses new sanitary sewers, the design will be based on current MSDGC standards. All sanitary flows will be transferred from the existing modeled sewer to the new modeled sanitary sewer. As a conservative assumption, all storm and/or RDII inflows will remain in the existing system. The RDII to the new system will be based on the current MSDGC standards. For MSDGC sustainable infrastructure modeling, the presumption is that a new stormwater system will be developed during sewer separation. The related presumption is that the separation of stormwater from the combined system will be incomplete. Stormwater may continue to flow to the combined system for several reasons: 1. Some stormwater connections will not be found, such as yard drains or sump pump connections inside homes. 2. Some stormwater connections will not be economical to remove, such as foundation drains. 3. Some stormwater inflow is the result of damaged pipe and/or manholes. The stormwater area remaining connected to the combined system will be estimated in one of two ways. The more detailed method is to determine at the parcel level which areas are likely to remain connected to the combined system or which areas are specifically routed to the storm system. The more general level is to estimate the fraction of the runoff area that is likely to remain connected. As a general rule, a minimum of 5 % of the original runoff catchment will remain connected to the combined sewer. The exception to this rule is an area without sanitary or combined sewers (parkland or hillsides) that drain into a definite stormwater system. Sewer separation will be modeled as splitting the base catchment into a stormwater catchment and a combined sewer catchment. MSDGC modeling policy is to maintain the total catchment area within the model input files. This policy allows verification of the conservation of total runoff results and allows future efforts such as installation of sustainable infrastructure, sizing of stormwater system, etc. The recommended method is described below: MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-28

86 MODELING SPECIFIC SITUATIONS 1. As a starting point in developing the stormwater system, the existing combined system will be mirrored by: a. Using the input files as a source of data tables to copy all nodes and links within the project areas. b. Renaming the nodes and links by ending the names with "S" for stormwater. c. Relocating the stormwater nodes and links by offsetting the X and Y coordinates of the nodes by a fixed distance (in the input file as [COORDINATES]). Suggested distances are 100 feet for both the X and Y coordinates. 2. Runoff catchments are duplicated and renamed with the "S" for storm designation. a. Outlet node names must also be edited for the stormwater catchments. b. Offset the X and Y coordinates of the stormwater catchments by the same distances as the nodes (in the input file as [POLYGONs]). 3. Adjust runoff parameters based on estimated effectiveness of separation. a. Area and percent impervious based on areas separated. b. Width determined from flow path length of areas separated or based on original catchment parameters Adjusted width = Original width / Original area x Adjusted area c. Other parameters may change for specific situations. 4. Assign last node in stormwater system as outfall or connect to other modeled stormwater systems as the situation merits. 5. Model runs should be performed to verify that the total runoff volume remains the same before and after development of the separated catchments. Information reviewed includes runoff volume, infiltration volume, evaporation volume, and peak runoff rates. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 6-29

87 VALIDATION 7. GUIDELINES FOR VALIDATION OF UPDATED MODEL Validation is required for each model received from MSDGC. Validation is the process of checking a hydrologic and hydraulic model against an independent dataset to verify the accuracy of the calibrated model. Validation is necessary for the following reasons: 1. The SWM may have been revised with updated information since the last set of calibration runs. 2. Validation ensures that the model is acceptable to use for the specific project s application. 3. During model calibrations, the limited observed datasets may create a bias within the model simulations to accurately represent only storms that are similar to the calibration storms. 4. To confirm that hydraulic and hydrologic systems behave as expected for a wide variety of storm events (rainfall volume, duration, and intensity). 5. Raise flags as to where uncertainty remains. Validation differs from calibration in that the validation runs should only be updated with changes to reflect the physical state of the sewer system and not for the purpose of matching the modeled flows to the validation data. When calibrating, model parameters are adjusted to make a model fit with measured conditions (measured flows or historic flood data). Once calibrations have taken place, the modeler should always validate the calibrations using independent storm events. 7.1 Validation Storms Validation storms are independent of the storm events used during the calibration process. They should be medium (6-month to 1-year recurrence) to large storms (greater than 1-year recurrence) with periods of dry weather flow both before and after the storm event. The dry period before the storm should be at least 1 day or until the system has returned to normal operation at WWTPs, storage facilities, EHRTs, etc. EPA s (1993) Combined Sewer Overflows: Guidance for Monitoring and Modeling states that an adequate number of storm events (usually 5 to 10) should be monitored and used in the calibration. The monitoring period should indeed cover at least that many storms, but calibration and validation are frequently done with 2 to 3 storms each (U.S. EPA, 1999). For a complete calibration and validation of a model, the storms used should include: Storms from all seasons because of variations in vegetation, evaporation, antecedent moisture, and rainfall patterns. Storms with a variety of recurrence intervals Storms with a variety of durations and/or back to back storms MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 7-1

88 VALIDATION Many factors will limit the number of storms used for the calibration and the validation of a model: Duration of monitoring for flow and rainfall Missing or otherwise unusable data from at least one monitor Multiple storms of similar recurrence interval and duration Time of year of monitoring available Abnormal weather conditions, such an existing snow pack or freezing rain instead of rainfall Operational issues, such as pump station failure, pipe collapse, high receiving water levels, or debris jams Appropriate level of effort Even when data are available, no improvement in calibration accuracy or acceptance in validation will occur using multiple storms of the same time of year, recurrence interval, duration, etc. Storms used in the validation process are generally less complete or differ from the ideal calibration storm. The validation storm can be atypical for rain pattern (uneven distribution or possibly clogged gauge) or antecedent conditions (abnormally wet or dry, or during high receiving water periods), occur during abnormal system operations (reduced WWTP capacity, malfunctioning pump station, etc.), or is missing data. Alternatively, validation storms can be storms not used in calibration when multiple storms of similar characteristics (intensity, duration, total depth, etc.) are available for calibration. Ideally the validation storms include at least one storm with a recurrence interval equal to or greater than the design level of the project. For combined sewers, the goal would be one or more storms at 1-year recurrence interval based the Typical Year modeling. For sanitary and storm sewers, the goal would be one or more storms with at least a 2-year recurrence interval based on level of service requirements. In cases where modeled basins are small and flow monitoring is not available, modelers may use historic flooding reports or observed surcharge events in the validation process. MSDGC standard practice is to use a minimum of three different storms where possible for validation and calibration (i.e., the storms used vary in time of year, recurrence interval [depth and intensity], and duration). Before starting validation runs, a review of the available flow survey data should be conducted. If the flow monitoring included a report with the data, the modeler should review the report for a better understanding of the project area and the available flow data. To verify that the data are consistent and reasonable, the modeler should also compare flow data to adjacent rain gauges and flow monitors. When comparing the modeled results with the observed data, the modeled flows and depths should be compared to the observed flows and depths. The two flow hydrographs should closely follow each other in both shape and in magnitude, until the flow has substantially returned to dry weather flow. The dry weather flow, in addition to the wet weather flows, should be considered during the validation MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 7-2

89 VALIDATION process. Observed dry weather flows should fall within the acceptable error bands. The modeler should document data analysis, data selection, and simulated results comparison in a report. More detail on documentation is provided in Section Expected Accuracy In 1993, the Wastewater Planning Users Group (WaPUG) created a Code of Practice for hydraulic modeling. The Code was last updated in The Code of Practice is divided into ten sections and covers model building for hydraulic analysis and testing, flow surveys and verification, and documentation. The WaPUG standard outlines an acceptable range for the percent difference of the observed data and the modeled results as a general guide to validation. The ranges are discussed in detail below. Because of the inherent error associated with flow measurement and hydraulic modeling, the range of acceptable percent difference along with hydrograph shape should be used in judging if a model is validated. Any claim that the validation is acceptable should be noted within the final documentation. The peak flow and volume statistics of the observed and modeled should be compiled and compared in a table. The acceptable percent difference range can be shown graphically by plotting two smoothed lines corresponding to the maximum and minimum percent difference from the observed data against the observed and modeled hydrographs. The MSDGC standard practice for smoothing is to use three-point centered smoothing. Figure 7-1 shows an example of the error bands Dry Weather Flow Dry weather flow (DWF) should be reviewed for a period falling at least three days after and one day before rainfall has been observed so that no runoff or infiltration has an impact on the monitored results. As with all cases of data selection, extra care should be taken to avoid using periods of incomplete or inaccurate data. The observed DWF should be based on at least 12 sample periods covering all four seasons for at least three different years. The intent of the spread in times is to understand the impacts of seasonal variation on infiltration included in the DWF. If a pattern of seasonal variation in DWF is observed, a period of 10 years should be examined to estimate the size and timing to the variation. The use of seasonal DWF patterns must be authorized by MSDGC. To be considered validated, the simulated DWF should meet the criteria of being within ± 10% of the observed DWF peak flows and volumes, according to the WaPUG standards. This criterion is separate from the wet weather criteria discussed below. The timing of the peaks and troughs should be within one hour of the monitored DWF. In some cases, not enough data is available to accurately represent a diurnal DWF time pattern. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 7-3

90 VALIDATION Figure 7-1 Example Plot showing Observed vs. Modeled Flow data and the Acceptable Error Bands MSDGC standard procedure is to use a diurnal DWF pattern. The validation target is ±10% of the observed daily average flows and volumes. The validation target for depth of flow is ±10% of the observed maximum depth during dry weather Peak Flow When comparing the hydrographs, modeled peak flows should be between +25% to -15% of the observed peak to be considered validated based on the WaPUG standards. The timing of the peaks and troughs should be similar for the observed and modeled flows during the event. A consistent time difference between the modeled and observed flows may indicate that the rainfall time is offset from the observed flow. A time difference of 1 hour is frequently the result of inconsistent consideration of Daylight Savings Time in the collection of rainfall and flow data. Observed flow data may contain noise not seen in the modeled data. Most flow measurements are calculations of flow based on separate depth and velocity measurements. Small fluctuations in either or both measurements will result in noticeably different results in the flow calculations. The modeler should review peak MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 7-4

91 VALIDATION flows, noting in the project documentation any possible over- or under-estimation of the peak flow by the flow meter Total Flow Volume The difference in volumes between the observed and modeled hydrographs should be in the range of +20% to -10% to be considered validated based on the WaPUG standards. The volume calculation should begin during the dry weather period before the rise in flows and to end after both the modeled and observed flow return to dry weather flow. For periods when the observed flow data are missing or deemed to be in error, the volume calculation for the observed and modeled data will not use those data points in either dataset Flow Hydrograph Shape The timing of peaks and troughs in a hydrograph should closely coincide with the goal of falling on the same or adjacent time steps. The flow charts will be visually inspected to ensure that the shapes of the modeled storm events are similar to observed data. The slope of the rising and falling limbs of the modeled hydrograph should be similar to those of the observed hydrograph. The time-to-peak is the length of time from the beginning of the rainfall to the peak flow, and is an important factor when comparing the shape of flow hydrographs. If a validation storm hydrograph has multiple peaks, the modeled peak flow should most closely match the largest observed peak in value and time step of the peak value Velocity Velocity measurements frequently contain noise in the observed data that makes comparisons between the observed and modeled results difficult. Smoothing of the observed data may be necessary. WaPUG does not have a standard for velocity error. The MSDGC model standard is to treat velocity similarly to flow. If the noise in the observed data allows, the general shape and magnitude of the velocity hydrograph should be similar between the modeled and the observed velocities Depth of Water The observed depth is usually the most accurate information available from flow monitoring. The depth sensor is less subject to error or fouling than the velocity sensor. Because the flow calculation depends on the both the depth and the velocity measurements, the error in the flow is sensitive to the error in the velocity. MSDGC does not use the WaPUG standards for the validation of the modeled depth of flow. According to the WaPUG standards, the calibration for the depth of surcharge should be within +1.6 feet (above) to -0.3 feet (below) the observed depth. For important points in the system, modeled values for unsurcharged depths should be within 0.33 feet (plus or minus) of the observed data. These standards do not account for the size of the pipe. For example, the allowable error in an unsurcharged MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 7-5

92 VALIDATION 18-inch-diameter pipe is 22%, while for an unsurcharged 72-inch-diameter pipe the allowable error is 5.5%. MSDGC standard procedure is to allow an error of ±15% of the observed depth. Because the modeled depth depends on the accuracy of the calculated flow and the assumed hydraulic conditions, the modeled depth is not expected to consistently match the observed depth exactly. In addition to errors in the flow calculation, the observed hydraulic conditions may change because of deposition and resuspension of sediment and debris, changes in operations, drowning of weir flow, etc. In addition to calibration to observed depth of flow, the modeler can verify the model accuracy by comparing scatter plots of the depth and flow. This plot will show if the modeled depth-flow relationship is similar to the observed relationship, even if the model is not accurately reproducing the observed peak flows. 7.3 Validation Results Compliance Validation assesses whether a model can accurately represent a variety of storm events with differing hydrologic and rainfall conditions. Three possible outcomes for the validation runs are possible according to the WaPUG standards: The model or part of the model is valid. The validation procedure identifies that the model is not validated, but this is not able to be resolved without further flow surveys or calibration runs. It is not possible to verify whether the model is validated. Once validation analysis is complete and the modeled results are suitably close to the observed flow data based on the MSDGC modeling standards, the model is considered to be validated. The modeler may then use the validated model with other sets of design storms or rainfall data to complete alternative analysis runs or other planning studies Non-Compliance If the MSDGC standards are not met by the validation runs, and the model cannot be validated, further investigations into the status of the modeling and subsequent results need to be performed. If the investigation into the model does not produce warranted reasons for the varied results, further analysis may be needed with a third independent dataset of storm events. In some cases, differing validation runs do not necessarily equate to failure. According to the WaPUG standards Version 3.001, It may still be possible to consider the model sufficiently verified in some circumstances provided that: The reasons for the non-compliance have been determined but cannot be modeled and have been assessed as not being important to the subsequent use of the model. The cause of the discrepancy cannot be isolated but an assessment of the effect of likely causes on the accuracy of the model has shown that this will not be detrimental to the purpose of the model. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 7-6

93 VALIDATION Infiltration is the cause of the discrepancy and this will be taken into account in other ways in subsequent use of the model. When the model validation fails, the modeler should document the extent to which the model is validated, plans to bring the model into validation/calibration, and arguments for and against proceeding with the project using the current model. The reasons for continuing with the project given the current model status may include the relative size of the areas that don t qualify as validated, or the degree to which the model (or parts thereof) are out of validation. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 7-7

94 CALIBRATION 8. CALIBRATION METHODOLOGY If the model does not meet the validation standards stated in Section 7, then additional calibration is required. Calibration will help to minimize the uncertainty within a model and to more accurately represent the physical system. The objective of calibration is to prepare a hydrologic and hydraulic model with sufficient detail to meet the analytical needs of the project. Calibration usually involves an adjustment of different model inputs (such as roughness) with the goal of creating simulated flows and depths comparable to observed data. Calibration is different than curve fitting or force-fitting. Parameters within the model should be changed to make the model more accurate and not be chosen arbitrarily to match the observed hydrographs. The following sections highlight the acceptable error, parameters to adjust, and other considerations during the calibration process. As with validation, MSDGC uses the following criteria as a basis for considering when a model is calibrated. Failure to meet these standards may justify MSDGC in considering the model uncalibrated and not useable for project development. The final model must be presented to MSDGC with a defense of calibration failures before the model can be used in for project modeling. 8.1 WaPUG Code of Practice for the Hydraulic Modeling of Sewer Systems The third edition of the WaPUG Code of Practice was updated in The standards for calibration are the same as for validation as discussed in Section Dry Weather Flow DWF should be reviewed for a period of at least 3 days after and 1 day before rainfall. A minimum of 12 dry weather periods covering 3 years and all four seasons is recommended. The simulated DWF should be within ±10% of the observed daily maximum flows and volumes. The modeled depth should be within ±10% of the observed daily maximum depth. MSDGC standard procedure is to use a diurnal DWF pattern. The calibration target is ±10% of the observed daily average flows and volumes Peak Flow When comparing the hydrographs, modeled peak flows should be between +25% to -15% of the observed peak based on the WaPUG standards. The timing of the peaks and troughs should be similar for the observed and modeled flows during the event Total Flow Volume The difference in volumes between the observed and modeled hydrographs should be in the range of +20% to -10% of the observed flow based on the WaPUG standards. The volume calculation should begin during the dry weather period before MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-1

95 CALIBRATION the rise in flows and should end after both the modeled and observed flow return to dry weather flow Flow Hydrograph Shape The timing of the peaks and troughs in a hydrograph should closely coincide. The modeler should visually inspect the flow charts to ensure that the shapes of the modeled storm events are similar to observed data. The time-to-peak is the length of time from the beginning of the rainfall to the peak flow, and is an important factor when comparing the shape of flow hydrographs. If a validation storm hydrograph has multiple peaks, the modeled peak flow should most closely match the largest observed peak Velocity The MSDGC model standard is to treat velocity similarly to flow. If the noise in the observed data allows, the general shape and magnitude of the velocity hydrograph should be similar between the modeled and the observed velocities Depth of Water MSDGC standard procedure does not use the WaPUG standards for depth of flow. MSDGC uses the target error of ±15% of the observed flow. 8.2 Selection of Calibration and Validation Storms Ideally, the SWM should be calibrated to at least three storms of different sizes, durations, and intensities. By calibrating to a wide range of storm types, the modeler verifies that the model can simulate flows matching various storms and not just forcing a fit to one type of storm. Whenever possible within the available monitoring data, three different storm durations should be selected: a short duration (1 to 2 hours or less) high intensity storm, a storm lasting a significant portion of a day (12 to 24 hours), and a storm that stretches over the course of more than 1 day. The short storm is intended to test the model response to immediate surface runoff and other direct inflows. The moderate duration storm is intended to test the model response for less direct flows to the sewers, such as I&I through storage areas. The long duration storm is to test the model response for deep infiltration. An additional consideration for storm selection is the intensity of the storm. Lower intensity storms aid in estimating the infiltration rates and the storage capacities. Higher intensity storms aid in estimating slopes, percent impervious, and sewer capacity. While validation is possible with two to three storms (Section 7.1), calibration should be undertaken with at least five storms (if the data are available) to achieve the range of storm durations, intensities, and rainfall depths desired. The varying storm sizes and durations will ensure the model is calibrated for the peak as well as the recession of the storm, which should match the hydrograph shapes. When determining which storms will be used for calibration and which for validation, emphasis will be given to using the better storms for calibration. Those storms with higher recurrence intervals, containing few to no missing or MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-2

96 CALIBRATION questionable observed data, and forming the widest variety in storm duration, intensity, rainfall depth, time of year, etc. are preferred. Storms used in the initial validation study may be used as calibration storms. These storms may not be used for validating the resulting calibration. Validation storms following calibration must always be different storms from the calibration storms Antecedent Conditions When selecting a storm to use for calibration, the modeler must not only look at the storm size, duration, and recurrence interval but also the antecedent conditions. To fully calibrate the model, calibration storms must begin and end at dry weather flows so that long-term infiltration and storage volumes may be considered. If the observed data for a particular storm starts after the onset of wet weather flow or ends before the full return to dry weather flow, consider using that storm for validation rather than calibration. If a storm of interest is preceded by another storm, the modeler may use an extended period (for example, three storms over 2 weeks) for calibration so that the dry weather flow requirements are met. Extended periods for calibration runs are frequently used for calibration storms during typical wet months, such as March and April. If multiple storms are modeled in a single time period, each storm is examined separately. Separately means that the comparison period for each storm is from the lowest flow between wet weather periods to the next low flow period Duration of Storms vs. Time of Concentration Ideally, the SWM should be calibrated to at least five storms of different sizes, durations, and intensities. One consideration in selecting storms for calibration is the duration of the storm and the time of concentration to and through the project area. When calibrating for peak flow, normally the highest flows for a given recurrence interval result from periods of rain close to the time of concentration of a sewershed. For example, if the time of concentration for a given CSO sewershed is approximately 15 minutes, higher flows would be expected from a storm with a 5-year 30-minute peak rainfall than from a 5-year 6-hour rainfall, even if the latter storm has higher total rainfall Continuous Period vs. Storm Duration Because the flow monitoring and rainfall data are collected as continuous periods, the modeler may choose to use a full monitoring period as a single model run instead of running a series of time periods for the storms of interest within the longer time frame. The continuous period modeling allows a consistent set of model parameters to be used for the model run to speed calibration for multiple events. When comparing the model results to the observed data, each storm should be examined separately. Each storm will have individual tables of results including comparisons of peak flow and volume, as well as plots comparing the observed data and the model results. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-3

97 CALIBRATION 8.3 Limitations to EPA-SWMM Calibration The EPA SWMM software has limitations that may inhibit calibration. Several model parameters are fixed values when the actual sewer has variable values. Some of the more common situations are discussed below Moving Sediment When modeling sewers, especially combined sewers, sediment deposit must be considered for calibration. The two methods for considering sediment are the filled circular pipe and editing the pipe cross section. The filled circular pipe is the preferred method for modeling sediment in that the depth of sediment assumed is shown in the model parameters. Unfortunately, the sediment feature is only available in the filled circular pipe. Editing the pipe cross section may be used for other pipe shapes but must be described in the model input file as the Description for the conduit and in the Notes area. However modeled, sediment in EPA SWMM is fixed for the duration of the model run. This fixing is in contrast to actual sewers where sediment is eroded for higher velocities and deposited when the velocities fall. Further complicating sediment modeling is that different materials erode and deposit at different velocities. MSDGC modeling practice is to assume no sedimentation unless information is available that describes stable sediment in a pipe segment. Stable sediment is sediment that is unlikely to move, such as accumulated cobbles or concrete that is too heavy for the expected velocities to mobilize Debris As with moving sediment, moving debris cannot be modeled by EPA SWMM. Various parameters that can be used for modeling debris are generally fixed values for the duration of the model run. For example, entrance losses or orifice coefficients at trash racks are normally modeled as flowing cleanly even when debris is likely during wet weather. With sufficient data, an approximation can be made for locations that are regularly blocked by debris. The modeler can develop a control curve for operating an orifice like a gate to represent the blinding by debris Inflatable Dam Weir Coefficients The weir coefficient for each weir in the model is a fixed value with a fixed width for the overflow area. In reality, the inflatable dam s shape may change with the air pressure and the depth and velocity of flow during overflow events. The MSDGC modeling standard is to use an initial weir coefficient of 2.50 as the low end of the expected range for a broad crested rectangular weir. The weir coefficient should be adjusted to improve calibration against observed data and expected impacts. 8.4 Calibration Discussion The adjustment of parameters to improve calibration is expected with the volumes and rates of water entering the sewers followed by adjusting the parameters MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-4

98 CALIBRATION controlling the flows within the sewer system. In general, calibration should follow the order of: 1. Dry weather flow 2. Runoff volume 3. Peak flow 4. Hydrograph shape 5. Depth of flow in sewer Adjustments that affect one goal usually affect other goals. For example, changing the minimum infiltration to improve the hydrograph shape will change the runoff volume and the peak flow. The subcatchment parameters used to model surface runoff are estimated with varying degrees of uncertainty. The modeler may perform a sensitivity analysis on the project area model to guide how adjustments to specific parameters impact the model results. A possible hierarchy of adjustment priority is: 1. Percent impervious 2. Width 3. Slope 4. Depression storage 5. Maximum infiltration rate 6. Minimum infiltration rate 7. Percent zero impervious depression storage 8. Surface roughness 9. Subarea routing For calibrating the hydraulic network, the losses at points of high energy loss (such as drop manholes, sharp bends, orifices, etc.) should be reviewed and adjusted first. General losses, such as Manning s n, should be adjusted after the review of point losses Incremental Sub-basins Flow monitoring may occur with upstream and downstream sites (i.e., the flow from one site is part of the flow measured at a downstream site as shown in Figure 8-1). For calibration to be valid, each site needs to be within the calibration limits. The upstream site (MC-LM-005) or sites should be calibrated before the downstream site (MC-LM-004). For areas outside the project area, the downstream site (MC-LM-004) should be calibrated so that the entire drainage area above the downstream site is calibrated (MC-LM-004 & MC-LM-005 catchments). If the upstream calibration (MC-LM- 005) is not acceptable, the tributary area between the upstream and downstream sites will be out of calibration to compensate. This method produces calibrated flows for the entire sewershed above the downstream site to convey to the rest of the system. When further work is performed to calibrate the upstream areas, the downstream calibration will be reviewed and adjusted. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-5

99 CALIBRATION Figure 8-1 Flow Meter Locations If the project area is between two flow monitoring sites, the calibration must be as accurate as possible for the project area. Whenever possible, the upstream observed data should be used as a time series input in place of the subcatchments and dry weather flow above the upstream site. In combination with the downstream observed flows, this method allows the most accurate calibration of the project area. If the upstream and downstream observed data are not both available for the calibration storms, the calibration of the downstream site should reflect the errors of the upstream site. For example, if MC-LM-005 overestimates the peak flow for a MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-6

100 CALIBRATION 6-month storm by 10 cfs, the calibration for MC-LM-004 should target overestimating the same peak flow by a similar 10 cfs. By maintaining a similar error, the project area will reflect the added flow expected between the two flow monitors. The use of incremental sub-basins is to calibrate specific areas within the SWM. For alternative analysis, the upstream model areas should be used instead of the time series Timing of the Rising Limb The start of the rising limb of the hydrograph depends heavily on the initial losses. The two most directly related parameters are the depression storage and the maximum infiltration rate. Because the maximum infiltration rate also influences the shape of the whole hydrograph, adjusting the start of the rising limb should be primarily done with the depression storage Surface Runoff Subcatchments and RDII Areas In some areas of the combined sewer system, the conditions are right for high infiltration to the combined sewers. These areas are shown in the very long recession limbs of the hydrographs especially following longer duration (12- to 24-hour) storms. These storms have enough rainfall depth and duration for significant amounts of water to infiltrate the soil column and reach the sewers. The primary impact on the model is the inability to match the hydrograph shape and volume while matching the peak flow using reasonable hydrologic parameters. For these situations, the modeler may include an RDII subcatchment in addition to the surface subcatchment to add flow to the recession limb of the hydrograph. Because this method has the potential to model the capture of more than 100% of rainfall, other explanations should be pursued before adding drainage area. Possible alternative explanations to long recession limbs include areas of low slope, additional drainage areas not modeled (especially at the edges of the sewershed), and stormwater storage areas. The MSDGC standard practice is to match the area and outlet node of the RDII subcatchment to those of a surface runoff subcatchment. In the RDII hydrograph, only the long term R3, T3, and K3 parameters will be used. The short- and intermediate-term factors are modeled by the surface runoff subcatchment. For areas with sufficient flow monitoring data (3 to 5 years), RDII factors for different seasons may be developed to reflect higher seasonal water tables or other factors impacting sewer infiltration. When using both surface runoff and RDII subcatchments, the volume of runoff must be carefully reviewed for reasonableness. With the potential for modeling more runoff depth than rainfall, other explanations to the long recession limbs should be pursued first. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-7

101 CALIBRATION 8.5 Output checks Different sources of model results will be used to judge the accuracy of the model. Certain data sources can point to model stability or other issues to focus the modeler s efforts on possible errors Continuity Error Review After running a simulation, the modeler should check the result of the continuity calculations in the status report. The continuity is categorized into Runoff Quantity and Flow Routing Continuity. The target continuity error for both Runoff Quantity and Flow Routing is 1% or less Rainfall The modeler will verify that the modeled rainfall output is correct. The total rainfall amount expected during the model simulation is calculated from the rain gauge network or radar rainfall database. The total precipitation expected from the rain data should match the Total Precipitation (depth in inches) under the Runoff Quantity Continuity section. If the total wet weather inflow volume found in the Flow Routing Continuity section of the Status is an unexpected volume, the modeler should verify that the rainfall and contributing subcatchment areas are appropriate for the sub-basin in question. Multiplying total precipitation depth by the sub-basin s total acreage provides a quick check in determining if the wet weather inflow volume is reasonable. The wet weather inflow volume found in the Status Report should never be higher than this calculated number. In most cases, the inflow volume will be less because of losses, such as infiltration and evaporation. One source of error in the runoff volume may be double accounting caused by using subcatchment runoff and RDII areas in the same sewershed Hydrology The Runoff Quantity breaks the total precipitation into evaporation, infiltration, runoff, and surface storage. The sum of the evaporation, infiltration, runoff, and surface storage must equal the rainfall. If the continuity error is larger than 1%, look at the Subcatchment Runoff Summary to see which subcatchments are unstable. Causes of instabilities include Percent Impervious greater than 100%, slope of 0%, and rainfall just before the end of the model run Hydraulics The Flow Routing Continuity ensures flow is not lost or improperly added to the system (i.e., node inflow = node outflow + flooding + storage). The internal outflow is flow volume lost from flooding manholes. These manholes must be reviewed against other information for confirmation of flooding locations. The flow routing continuity error should be less than 3%; if not, the modeler should look at the Highest Continuity Errors located in the status report. Look at the hydrograph and sewer profiles for the nodes with the highest continuity errors, and determine the problem areas. Continuity errors can be the result of abnormal weir or orifice coefficients. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-8

102 CALIBRATION Acceptable changes to the model parameters to improve continuity can be categorized as general model parameters and specific component parameters. The general parameters that change the calculations for the entire SWM and may improve continuity include increasing the conduit lengthening parameter, reducing the routing time step, and increasing the default minimum surface area. Specific component parameters change the model calculations for individual SWM components and include increasing storage volume, small changes to roughness, and changes to slope. Other parameters may be changed on the judgment of the modeler. Preference is given to changing individual components rather than to risk changing the calibration of the entire model Node Flooding One reason model results may not match observed data is that nodes are flooding in the model. Flooding refers to all flow that exceeds the maximum allowable depth in a node. The flow will exit the node and will be lost from the model (ponding is not allowed), which will affect both the hydrograph shape and the total volume calculations during calibration. As stated in Section 5.7.1, ponding can be modeled for individual manholes, as necessary. The first review of flooding is the check by volume to find the largest volumes to focus review on. The second review is the flooding duration hours flooded, as long flooding time periods may indicate a hydraulic problem such as an improper pipe diameter or a malfunctioning Control Rule. Very small durations in the hundredths of hours are likely the result of model instabilities, especially when the flow rates are high and the volumes are very low. These instabilities can be reduced or eliminated by changes to the hydraulic network, such as small changes to energy losses or the addition of a small amount of storage. During calibration efforts, modelers should review the node flooding table for new locations or significant changes in peak flow, total flooding volume, or duration of flooding. 8.6 Standard Tables, Plots, and Summary Discussion Requirements During the course of model calibration and/or validation, the modeler should consider ways of presenting the data that was reviewed, used, and analyzed for the project. Documentation should include analysis on the rainfall and observed flow data, charts on the simulated versus observed data, and the final resulting graphics and conclusions. Section 9 provides further detail on model validation and calibration documentation. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 8-9

103 DOCUMENTATION 9. GUIDELINES FOR DOCUMENTING CHANGES TO THE MODEL Modelers should document the steps taken from the time of acceptance of the SWM from MSDGC to the calibrated project model. The documentation serves two primary purposes: model management and future reference. MSDGC manages the changes to the SWM by reviewing and accepting changes to the model in phases. Using phases instead of reviewing and accepting a final product reduces the possibility of non-standard or incorrect changes to the SWM. Each phase is an opportunity for MSDGC to provide guidance on changes and to provide updated information to the model from internal MSDGC sources and other organizations working in the MSDGC service area. The documentation also gives MSDGC information sources for future reference about how and why changes were made to the SWM, the impacts of those changes, the limitations of the information used and modeling results, and suggestions for future efforts to improve the SWM. A sample report is included in Appendix B. 9.1 Reports by Modeling Phase The following technical memoranda should be submitted to MSDGC for review and acceptance at key points in the model development: 1. Model Review Results of the initial review of the model parameters and available data sources, as well as the proposed changes to the model 2. Model Changes Changes, information sources, and justifications 3. Model Validation Results of the model validation including proposed changes 4. Model Calibration Results of calibration and re-validation These technical memoranda may be delivered to MSDGC as appendices to larger project reports. For example, the Model Review memorandum may be included as part of a Data Collection Report that includes information on available and needed data for the rest of the project (such as geotechnical, operational reports, etc.). An alternative method of delivering the required reports is to combine them into an overall project report. At each phase, the report is appended so that the report includes all information required from the beginning of the project to the current phase. This method of reporting allows the generation of a single source of information for later reference and provides a narrative on the development of the project model Model Review Report The Model Review Report discusses the results of the review of the model parameters with a focus on parameters outside expected values, any proposed changes to the existing model based on the initial review, and the available data sources. Sections in the Model Review Report should include: 1. Project and project area descriptions 2. Description of SWM provided by MSDGC MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-1

104 DOCUMENTATION 3. List of model parameters outside of expected values 4. Proposed changes to model parameters based on the review 5. Description of available data, such as as-built drawings, previous flow monitoring, etc. 6. Data collection plan to retrieve known data sources and to investigate others, as well as such measures as flow monitoring, site visits, and surveying Model Changes Report The Model Changes Report extends information in the Model Review Report to include the changes made to the SWM and the justifications for the changes. Sections in the Model Changes Report should include: 1. Description of data sources used, such as as-built drawings, previous flow monitoring, etc. 2. References and methods for determining parameters 3. General description of changes and justifications 4. Appendix containing a full list of parameters changed Model Validation Report The Model Validation Report describes the results of the validation of the updated SWM against the available observed data. Sections in the Model Validation Report should include: 1. Description of the flow and rain data sources used for the validation 2. Justification of the storms used 3. Recurrence interval and other descriptions of the storms used 4. Justification of the flow data used 5. Tables and graphs comparing the observed and modeled flows and levels 6. Discussion of the results of the validation 7. Justification of accepting model as validated or not 8. If SWM not validated, plan for data collection and model calibration Model Calibration Report If the model was not accepted as validated in the Model Validation Report, the Model Calibration Report describes the efforts to calibrate the updated SWM against the available observed data. Sections in the Model Calibration Report should include: 1. Description of the flow and rain data sources used for the calibration 2. Justification of the storms used for calibration and validation 3. Recurrence interval and other descriptions of the storms used 4. Justification of the flow data used 5. Tables and graphs comparing the observed and modeled flows and levels 6. Discussion of the results of the calibration and validation 7. Justification of accepting model as validated or not 8. If the SWM is not validated even after calibration, a plan for project modeling moving forward MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-2

105 DOCUMENTATION 9.2 Model Review Documentation In a general sense, the Model Review Report provides a synopsis for a Who, What, When, Where, and Why for the project that the text is based on. A background on the project is provided in the report, as well as a brief history of the SWM provided by MSDGC. Once the project has been adequately described, an initial survey of the model and its parameters should be documented. Any changes proposed as a result of the first look (and the ways to attain information regarding these changes) should be included in the Model Review Report Modeling Project and Project Area Description The introductory paragraphs for the Model Review Report (as well as the overall project report) should provide details regarding the project modeled and a description of the area where the project takes place. The project description should outline what is going to be modeled, the purpose of the modeling effort (historic calibration, alternative analysis, post-construction simulation, etc.), who is involved on the project team, and the general time-frame for which the work should be completed. In addition to text describing the project area and the boundaries of the watershed, the report should include a vicinity map and location schematic outlining the key components of the sewer network Boundaries of Modeling Project Upon receiving a portion of the SWM, one of the first steps is to verify and note the boundaries of the modeling project. Modelers should delineate and confirm that the specific project area of interest is included within the sewer model received. System features, such as SSOs, CSOs, and other key elements, should be identified for inclusion within the modeled system and the parameters verified for accuracy and completeness Boundary Conditions Files Used For the Final Model Boundary conditions are typically needed unless the project involves working with the SWM in its entirety, a complete sewershed network, or an area not restricted by an elevated hydraulic grade line downstream that impacts the project area. After the sewershed has been analyzed, suitable boundary conditions should be set up for modeling assessments. Defined boundary conditions (head and/or flow) should sufficiently recognize upstream and downstream influences. Other projects upstream or downstream of the project area may impact the boundary conditions. Information on how the boundary conditions were developed should be documented so that the starting conditions can easily be replicated. The source of the model in which the boundary conditions were obtained along with the specific node or conduit information should be included in the documentation. Accurate boundary conditions are essential for comparing base conditions to the updated model, as well as creating project alternatives for future development. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-3

106 DOCUMENTATION Boundary Conditions Files Provided by Others In some cases, other organizations may provide boundary condition time series files based on the projects they have worked on and developed within the study area. These files representing projects should be included within the final models delivered to MSDGC Boundary Conditions Files Used by Modeler to Speed Development Computer models can represent enormous amounts of the sewer network. The system can become so immense that the models can take days to complete a single simulation. To overcome the time barrier that may hinder a project s development, boundary conditions may be used at various points in the model to replace part of the modeled network. Once the network has been reduced, calculations can be processed more quickly, reducing simulation time. However, the boundary conditions files used by the modeler to speed model development must be replaced by model elements for the final models delivered to MSDGC. Using the entire system ensures completeness and allows the flows to interact dynamically throughout the piping network Projects Outside the Project Area Developed by Others Occasionally, projects are being planned or constructed concurrently and in the general vicinity of one another. Projects that are outside of the current study area but still have an impact on the flows (upstream or downstream) should be included within the model as part of the boundary conditions. Documentation should be included on who is developing the project outside the work area, what the changes include, and how the changes affect the area of interest. An example is a project that includes increasing the capacity of an upstream HRT facility. Doing so would in turn produce a higher starting inflow value for the area of interest. The boundary conditions should be listed for reference Description of SWM provided by MSDGC To properly document changes to a model, the modeler must provide a clear description of what model was changed. Documentation must establish and describe what model was received from the client and the date model files were transmitted. This information will help maintain which version of the model was included in the original files before any changes were made. The project description will help later users understand the history behind the model and the date it was last updated. The description should also summarize the intended purpose for which the model was developed and should be used for in the future. Also included in the project description should be the software type and version that was used to develop the project model. SWMM models contain a Title/Notes section within the Data Browser of the Data tab. In this section, modelers should update the text when working on a project. Text should contain, but not be limited to, the following: Dates of when the SWM was last updated MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-4

107 DOCUMENTATION Organization making changes Sources/locations of used information All changes made during the update Dates the updates were made Updating the model description is for the convenience of MSDGC and other modelers who will use the model at a later date. Once the model s background has been established, a description of the current project should be noted. A synopsis of the work completed for the current project should be added, including major changes to be made to the model Model Parameters Outside of Expected Values After receiving a portion of the SWM from MSDGC, modelers should thoroughly review and vet the input deck against data from the GIS dataset and other reliable sources of information. A preliminary review of model hydrology and hydraulics should be undertaken and data needs assessed and identified. Model attribute information should be reviewed against GIS and any discrepancies resolved through the SWM Work Plan that is associated with the sewershed model. Model input parameters will be reviewed for completeness and possible anomalies noted for investigation. If the model s input deck contains extraneous parameters that are unrealistic or outside the range of expected values, they should be listed within the Model Review documentation. For instance, if a subcatchment is found to have a percent impervious value greater than 100, the feature should be listed in the text Proposed Changes to Model Parameters Based on Review When values are found to be outside the realm of feasibility, a proposed change to the value should accompany the parameter in question. Proposed solutions for the data values may be corroborated with the GIS dataset on file, record drawings, field verification, or by any means necessary to obtain accurate and up to date information. The source of the proposed value will be documented Description of Available Data The Model Review Report should contain a list of all available information for use pertaining to the project area. Past projects developed or known future projects planned should be listed with a description on how that work may impact the current study area. The availability of as-built drawings, previous flow monitoring studies, results of past modeling of the project area, or any other viable sources of information relating to the project should be documented Data Collection Plan Once the modeler has an understanding of all documentation or observed data available for the project area, a data collection plan should be established. The collection plan outlines how the modeler is proposing to obtain the known information, and collecting resources that may not be readily available. If more data is required to accurately perform the project work, the data collection plan will identify additional sources of information and methods for retrieving it. Planned MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-5

108 DOCUMENTATION field work, such as flow monitoring, site visits, or surveying, should be documented in the Model Review Report. 9.3 Model Changes Documentation The Model Changes Report is a technical memorandum detailing every revision made to the system for modeling purposes. After the project area has been established and boundary conditions are in place, changes to the catchment delineation, collection system, and/or modeling parameters may be needed to meet project modeling objectives. Once the model has been received from MSDGC, documentation should begin and continually be updated as needed so that the final changes list and reasons for the changes are complete and accurate. The model changes documentation should include the old value, the new value, and the reason for the change. As reports can become separated from the model input file, model changes should also be documented in the model input filed using the Description field Description of Data Sources Used Sources of information and materials used should be documented as the modeling project progresses. Changes and modifications are continuously being made to improve the MSDGC collections system. As a result, updates need to be made to the SWM to reflect the changes that are occurring in the actual system. Documentation begins at the same time as the initial stages of the model investigation. Any time a model feature is deemed worthy of a change, the update must be logged with a description of the data source used for future reference. In each case, all changes should be recorded, along with a justifiable reason on why the change needed to be made. Possible changes to the system that warrant a change include: Recent development or construction projects that change the catchment parameters and/or dry weather flow amount New record drawings, or discovery of old plans indicating construction or replacement of the existing sewer system Changes to pump curves or operating rules at regulators or RTC facilities Updated aerial photography and contour information Surveys and inspections of the basin area and sewer infrastructure Updated observed rainfall data and flow monitoring data Updates made during model calibration runs References and Methods for Determining Parameters When parameters are changed, the source of information for the updated value should be documented. This documentation will also take place when initial values are used from various sources and adjusted for improved calibration. Typical sources include: Text or other reference books MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-6

109 DOCUMENTATION Publications Survey data Site visit Aerial photo As-built or other drawings Discussions with MSDGC or other field staff When documenting data sources, the reference is to include dates and other information to allow later users to determine if more recent data are available in cases of conflicting information. When using derived information to update the model, the methodology should be briefly discussed. For example, assume that GIS aerial photos and combined sewer catchbasin locations are used to estimate the maximum flow path length from the edge of the catchment downhill to the first catchbasin. In this example, the methodology might be described as: From the flow path length and the subcatchment area, the width was calculated as the area divided by the flow path length General Description of Changes Within the Model Changes Report text, a general description of the changes made to the model should be included. For example, assume that a section indicates that percent impervious values were increased for several catchments to calibrate the peak flow rates and runoff volumes. In addition to documenting the changes to the model, a formal justification is needed on the reason for the change (calibration to observed data in the example). Some possible reasons for change include, but are not limited to, the following: Record (as-built) drawing corroboration Review reports related to the project area and the sewer system Site visits and field verifications Meetings or other communication with MSDGC personnel Detailed review of flow monitoring and other observed data Engineering judgment based on updated aerial photography and contour information Appendix Containing all Parameters Changed A technical memorandum must be submitted to MSDGC documenting all the changes to the model inputs. All individual changes should be listed in an appendix, along with justification for the changes. The completed documentation should be included in both the Model Changes Report and the final submittal so that subsequent users of the model may develop a project work plan. The SWM Work Plan can then be updated with information about when the SWM was last updated per justifiable changes such as GIS, field verifications, record plans, and/or calibrations. An example of this documentation can be found in a future update. Note that only changed parameters are listed to ease review of the information. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-7

110 DOCUMENTATION Additionally, all updated datasets and model results must be submitted to MSDGC using the standard modeling software along with any recommended changes to the GIS dataset maintained by MSDGC. Any changes made to the model should be noted as a text line in the model itself. 9.4 Model Validation and Calibration Reports The model, whether updated or not, should be compared against representative storms to show that the model recreates the sewer system s response to rainfall. The Model Validation Report and the Model Calibration Report show the accuracy of the model and describe any efforts to improve its accuracy. The Model Validation Report describes the results of the existing model following update of model parameters to actual conditions. The Model Calibration Report describes the results of adjusting parameters to better match observed data. The Validation Report stands alone. The Calibration Report may contain parts or all of the Validation Report in the Calibration Report text or as an appendix Description of the Flow and Rain Data Sources Used The first step in flow monitoring documentation is to discuss the locations of the data collectors used for the analysis. Data collection includes both rainfall and flow monitoring data. MSDGC uses weather radar technology as well as rain gauges to observe and record rainfall data. It is MSDGC s preference to use radar rainfall data as much as possible. If radar rainfall is utilized, a discussion on the radar bins and whether the single point method or average area method is used should be documented (see Section , Radar Rainfall). Whether radar rainfall or rain gauge data are used, a table or graphic should indicate which catchments are associated with each particular rainfall location entity. Because rainfall is spatial in nature, not all radar sub-basins or rain gauges will experience the same rainfall volumes and intensities through the course of each storm event. Figure 9-1 shows an example of rain gauge and flow monitor location graphic. Flow monitors should be described with the manhole number in which they were installed, the size of the contributing sewer, and the amount of contributing acreage associated with each meter. Table 9-1 shows an example of a flow monitoring summary. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-8

111 DOCUMENTATION Figure 9-1 Example of Rain Gauge Network and Flow Monitoring Locations Table 9-1 Example Flow Monitor Location, Contributing Inflow Pipe and Acreage Meter Manhole Inflow Pipe Contributing Area (Acres) FM - # " Storm Sewer 255 FM - # " Combined Sewer 455 FM - # " and 48" Combined Sewer Branches 122 FM - # " Combined Sewer Branch 197 MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-9

112 DOCUMENTATION Justification of the Storms Used When choosing validation and calibration storms, the modeler should screen the available radar rainfall and rain gauge network data. The local rain gauge data should be reviewed, as well as surrounding rain gauges, to ensure the data are reasonable and that extreme outliers are not present. An outlier should be considered extreme when it has a recurrence interval significantly higher in comparison to other rainfall and flow data. The number of storms used to cover the range of possibilities can be as many as 30 to 50 storms. Many factors will limit the number of storms used for the calibration and the validation of a storm. Duration of monitoring for flow and rainfall Time of year of monitoring available Abnormal conditions Missing or otherwise unusable data from at least one monitor Appropriate level of effort Even when data are available, no improvement in calibration accuracy or acceptance in validation will occur using multiple storms of the same time of year, recurrence interval, duration, etc. Three or more storm events should be documented for validation purposes. Validation storms generally are medium to large rain events that may contain atypical rainfall patterns or antecedent conditions to test the system. The modeler should document and be able to justify the reasons for use of the validation storms. If the model is not validated, at least five calibration storms should be selected (if the data are available) to minimize the uncertainty within the model. These events are to vary by characteristic (intensity, duration, total depth, etc.). If the goal is CSO reduction, calibration storms should remain within reasonable magnitude of events observed throughout a typical year. If alternatives are being considered for the system, storms with large recurrence intervals may be desired. New infrastructure may need to be sized for the MSDGC stormwater regulations, which include design for the 10-year storm and checks of the 25-year and 100-year results. Usually the better storms are selected for calibration purposes versus saving them for validation runs. As more data become available, however, a higher number of storm events and graphs should be included to accurately reflect the changes that were made to the model. In the end, the modeler s duty is to justify why the storms were selected for the project. The reasons should be documented within the Validation Report and Calibration Report for future reference Recurrence Interval and Other Descriptions of Storms Used For each of the validation storms and calibration storms used, the recurrence interval of the storm will be noted. An infinite variety of storm events is possible because of combinations of rain coverage, intensity, temporal pattern, and total rainfall. Two publications are available detailing storms for the Cincinnati area. Bulletin 71 of the MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-10

113 DOCUMENTATION Rainfall Frequency Atlas of the Midwest and NOAA Atlas 14 of the Precipitation- Frequency Atlas of the United States both give a table of rainfall depths for storm recurrence intervals and duration. Modelers should include a table showing each storm event (start and end dates, rainfall depth, and maximum intensity) after the storms have been selected. For each validation or calibration rain event, the radar sub-basin or rain gauge used, duration of the storm, total rainfall, and peak rainfall intensity should be listed, as shown in Table 9-2. A second table will review the recurrence intervals for four significant time spans, as shown in Table 9-3. The 15-minute period reflects the time of concentration of smaller sewersheds in the MSDGC system. The 1-hour period is useful for larger sewersheds and is familiar to many modelers. The 6-hour period reflects the time of concentration to the SWM WWTP in most models. The 24-hour period is another familiar period for many modelers and reflects the period that is likely to impact storage facilities. Discussion on the storms used for validation and calibration should also include any relevant information on: Inter-event period used to isolate storms o Statistics will include both 3-hour and 6-hour inter-event periods Antecedent conditions including length of time since previous rain Temperature-related conditions, such as abnormally cold periods or the existence of snow pack Differences in timing, duration, depth of rainfall, and intensity for the rain data used for the project Reasons for concern such as possible clogging or the lack of high recurrence interval storms Justification of the Flow Data Used All flow monitoring data are not of equal quality. Some sites are challenging, because of extreme variation of flow from dry weather to wet weather peak flows. Other sites have problems with sediment and debris damaging or burying sensors. Good sites will have occasional problems that cause poor quality data for a limited time. One-time events, such as unusual debris loads, flow monitoring equipment failures, downstream blockages, etc., may prevent the use of a flow monitoring site for a particular storm. The discussion on the flow monitoring data should include the limitations of the available data and the resulting calibration. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-11

114 DOCUMENTATION Table 9-2 Example Wet Weather Events Event Name Start Date & Time End Date & Time Duration (hrs) Total Rainfall (inch) Maximum 5-Min Intensity (in/hr) Storm 1 3/1/10 12:30 3/3/10 6: Storm 2 3/18/10 4:00 3/19/10 21: Storm 3 4/2/10 3:45 4/6/10 13: Storm 4 4/24/10 19:45 4/25/10 1: Storm 5 6/12/10 14:00 6/14/10 8: Table 9-3 Example Recurrence Intervals Table Event Name Storm 1 Storm 2 Storm 3 Storm 4 Storm 5 Peak Depth (inch) 15-Min 1-Hour 6-Hour 24-Hour Recurrence Interval Peak Depth (inch) Recurrence Interval Peak Depth (inch) Recurrence Interval Peak Depth (inch) Recurrence Interval MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-12

115 DOCUMENTATION Available Data Quality The documentation should include a discussion on the quality of the available flow monitoring data for validation and calibration storms. The discussion should include any known problems generally at each site and for specific storms. For example, if site has a history of sediment blocking the velocity measurement, the discussion should include this information and the impacts on validation and calibration. Another example is when snowmelt is known or suspected of causing abnormally high base flows through a storm event. The discussion on data quality will include the evidence for snowmelt and the impacts on the modeling results Challenges in Validation and Calibration Continuing the data quality discussion into the use of the data with the model, the documentation should include discussion on the challenges to validation and calibration. Topics to discuss include upstream flows higher than downstream flows, chronically missing data during high flows, manual operations such as gate closures and pump rates, high receiving water levels, and snowmelt. The discussion should include which storms at which flow monitoring sites should not be considered as part of the calibration and validation statistics Tables and Graphs Comparing Observed and Modeled Flows and Levels Calibration and validation graphs should be included in the documentation package for each storm event used. Included on the graphs should be the observed and modeled data for a validation or calibrated storm event. A secondary axis indicating cumulative rainfall for the storm event should also be included. On each graph, an error band around the observed data should be added. The error band is drawn to reflect the plus/minus range of the WaPUG standards (or similar guidelines) and to ensure that the modeled data criterion is met. Modeled data should be within the error bands to be considered acceptable. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-13

116 DOCUMENTATION Figure 9-2 shows an example of a modeled storm compared to observed data with error bands added to the graph. Normally the graphs are included in the documentation as an appendix. At times, observed data are not always smooth and can look like static depending on the quality of the flow monitoring location and local flow conditions. Examples include sites downstream of a pump station or where a hydraulic jump frequently occurs. To correct this situation, a smoothed average of the observed data may be added to the charts. Figure 9-3 shows an example of the modeled data compared to the observed data with an hourly average added in. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-14

117 4/9/09 0:00 4/9/09 12:00 4/10/09 0:00 4/10/09 12:00 4/11/09 0:00 4/11/09 12:00 4/12/09 0:00 4/12/09 12:00 4/13/09 0:00 4/13/09 12:00 4/14/09 0:00 4/14/09 12:00 4/15/09 0:00 4/15/09 12:00 4/16/09 0:00 4/16/09 12:00 4/17/09 0:00 4/17/09 12:00 4/18/09 0:00 Flow (mgd) MSDGC SWM Modeling Guidelines & Standards DOCUMENTATION Figure 9-2 Example Observed vs. Modeled Flow Data and Acceptable Error Bands Figure 9-3 Example Calibration or Validation Plot with Smoothed Observed Data 1.4 Site 16 - Flow - April Storm Observed Modeled Cumulative Rain Observed Hourly Avg MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-15

118 DOCUMENTATION Graphs representing the modeled simulation results versus observed storm events help the reader visually understand the data. In addition, tables summarizing the observed peak flow, total volume, and peak depth values that were monitored in the system should be compared with the simulated model results. Challenges to calibration or other notes should be included in this table. The percent difference will ultimately be the factor determining whether the model is in compliance. Table 9-4 is an example of documenting the percent differences in tabular form. Timing of the peaks and valleys for each hydrograph is one of the characteristics to be noted which is hard to define with numbers. In this instance, modelers can create a table with each storm event and simply state whether they believe the shapes of the hydrographs are within calibration standards. Table 9-5 is an example of this type of table Overall Discussion of the Results While the earlier discussions focused on the results of the calibration and validation for each flow monitoring site, the documentation should discuss the modeling results in the aggregate. Part of this discussion should be the relative importance of the sites discussed above. If a site is poorly calibrated but represents only a tiny fraction of the model, is further time and effort in improving the calibration of value to MSDGC? Is the model generally well calibrated in the project area but less well calibrated elsewhere? Justification of Accepting Model as Validated The desired situation is for the calibration and validation storm simulations to be within the modeling standards for all storms for all calibration points. In this case, the modeler summarizes the model comparison results and states that the model is acceptable as validated. When the model is out of validation for significant sites, the modeler should state that the model is out of validation based on those sites. The discussion should include possible sources of model error and observed data problems. When the monitoring sites important to the project are not fully in validation, the documentation must defend the declaration of validation or non-validation. The discussion should include information on the storm or storms that are out of validation. Part of the discussion should include the importance of the sites and storms out of validation, as well as the importance of those in validation. Whether the model is considered validated, the discussion should include the impacts of those sites or storms that are not in validation. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-16

119 February 26 - March 3, 2009 February 26 - March 3, 2009 Storm MSDGC SWM Modeling Guidelines & Standards DOCUMENTATION Table 9-4 Example Peak Flows and Volumes for a Wet Weather Event Site Peak Flow (mgd) Total Flow Volume (MG) Observed Modeled % Difference Observed Modeled % Difference Comment % % % Debris on velocity probe during % storm % % % % % % % % % Debris on velocity probe during storm % % Table 9-5 Example Visual Checks for Peak Timing and Hydrograph Shape Storm Site Time to Peak Hydrograph Shape Comment 6 Good Good 8 Unknown Unknown 11 Good Peak Good, Recession Unknown Debris on velocity probe during storm 12 Good Fair 13 Good Poor Underestimates recession 14 Good Good 16 Good Good 17 Good Peak Good, Recession Unknown Debris on velocity probe during storm 19 Fair Poor Peak early, Underestimates recession MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-17

120 DOCUMENTATION Resulting Course of Action This section of the documentation addresses two issues: project-based actions and SWM actions. For the project-based actions, the focus is on developing an existing conditions model that represents the sewer system within the limits of calibration. For the SWM actions, the focus is on improvements that may be needed for other projects or the SWM as a whole to improve calibration Project-based Actions Project-based actions are recommendations for achieving calibration if the model is not validated. For the validated model, the section of the documentation is simply a restatement of the validation results. For models that are not validated, this section of the document discusses the recommended steps to improve the model to achieve validation. Possible recommendations include: New flow monitoring and rain gauge locations Extending flow monitoring at existing or previously used sites Additional field work such as percolation tests, SSES studies, CSO regulator inspections, and surveys Changes to modeling methodology to more completely represent the conditions in the sewer system Included in the recommended steps should be discussions on the required time and budget for the steps. The discussion should also include the impacts on the current project schedule and budget. One option to include is using the model for the current project with the knowledge of validation problems. The discussion then focuses on how the model can be used in the absence of alternative methods for sizing solutions and testing impacts. The use of qualitative measures may be necessary to move the project forward. If the model is known to overestimate peak flows, for example, sizing solutions to match or reduce modeled peak flows may be the best method of proceeding. In this situation, the project would be reducing any problems associated with peak flows even if the extent of the reduction cannot be quantified SWM Actions As an expert on the SWM for the project area and familiar with possible problems with the SWM, the modeler can advise MSDGC on areas for improvement in the SWM. The modeler should discuss recommended monitoring not currently in progress, sites for field inspections, etc. 9.5 Impacts of Changes Changes to the model parameters are expected to result in changes to the model results. The documentation of the changes will include discussion and tables describing the impacts of the changes. Of primary concern to MSDGC are the volume and frequency of CSOs, SSOs, and flooding manholes. For examining the impact of the changes on these statistics, the MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-18

121 DOCUMENTATION original MSDGC model and the updated model will be run for the 1970 Typical Year rainfall. The inflow volumes, the overflow volumes, and the number of overflow events at CSOs and SSOs in the Typical Year will be compared between the two versions of the SWM. For flooding manholes, the statistics will be the total overflow volume and the number of overflow events. For separate sanitary areas where projects are sized for design storms, the statistics for the SSOs and flooding manholes will be based on the required design storms. Normally, these storms are the 2-Year and 10-Year 24-Hour storms. For projects in areas with basement flooding, overflowing manholes, or other reported or possible problems related to water surface elevation, profiles for the areas of concern should be developed. The profiles are compared to the original and the existing models with observed or reported problems. The accompanying discussion should include the uncertainty in the model results, the impacts of the proposed project, and the need for mitigation. 9.6 Conclusion The modeler should provide both an executive summary and a conclusion as part of the final piece of documentation. These sections will discuss the process of updating and validating the SWM for the project. The results should be summarized and the acceptance of validation or non-validation should be briefly discussed. 9.7 References Documentation of sources used for the project is important in that values used for modeling parameters may come into question at some point in time. The modeler should cite reference materials used throughout the course of the project. When possible, the cover page and the specific pages of reference materials should be included as an appendix. MSDGC Modeling Guidelines & Standards Revision 2 June 2012 Volume I 9-19

122 Appendix A SYSTEM WIDE MODEL WORK PLAN

123 Appendix B STANDARD FORMS AND REPORTS

124 Model Request Form GENERAL INFORMATION Submitters Name: Date: Phone: Project Name: Project Type: Asset Management Wet Weather Improvements Program (WWIP) WWIP No: CIP Number: Project Description: MODELING REQUESTED (date requested by:) Emergency Modeling Purpose: Planning Level Preliminary Design Final Design PTI Application WIB Investigation As-Builts Model Requested: Existing System Wet Weather Improvements Year 2025 Growth Overflows Affected: CSO: SSO: PSO: Describe Required Modeling: MODELING OUTPUT REQUIRED MODELED STORMS Modeled Profile (please attach map or list of manholes to include in profile) Peak Instantaneous Flows: cfs mgd Peak Hourly Flows: cfs mgd Sewer Numbers: Average Dry Weather Flow: cfs mgd Sewer Numbers: Overflow Volume [MG]: CSO: see attached (differential change) SSO: (includes MH overflows) PSO: Number of Overflows: CSO: see attached (differential change) SSO: PSO: WIB Investigations (Existing System: 6-mo, 2-yr, 5-yr, 10-yr Storms) Sanitary Sewers (Existing System: 2-yr Storm; Proposed System: 10-yr Storm) Combined Sewers (Existing System: 2-yr Storm; Proposed System: 10-yr Storm) SSO & PSO Overflows (Existing & Proposed Systems: 2-yr Storm) CSO Overflows (Existing & Proposed Systems: Typical Year Storms)

125 I. Project Team System Wide Model Report <Project Name> Project No. <CIP Number> Modeler: <Modeler Name> Project Manager: <Project Manager Name> Flow Monitoring Lead: <Flow Monitor Lead Name> II. Key Milestones Model Request Submitted: <Date> Final Model Results/Report Submitted to Planner: <Date> III. Project Summary Location: <General Description of Project Location may include city name, streets, etc.> The Problem: <Brief description of the problem> Type of Project: <Asset Management or WWIP> Project ID: <CIP Number> Sewershed: <WWTP Name> Tributary to CSO/SSO: <Overflow Number> Sewer Type: <Public, gravity, force main, etc.> Flow Monitoring: <State if additional monitoring was recommended> IV. Modeling Scope <Brief scope of project, after discussion with Project Manager>

126 V. Modeling Assumptions <At a minimum, include storms evaluated, date of last update, date of last calibration, etc.> VI. Results <Discuss results and attach applicable figures to the report> <The figures must include a profile and GIS plan view map.> <State that the MSDGC Modeling Guidelines and Standards were followed. If there were variances from the Guidelines and Standards briefly state what they were and the basis of the decision.> VII. Conclusion <Concluding text including any recommendations>

127 <PROJECT NAME> SYSTEM WIDE MODEL VALIDATION REPORT CIP # < > <TASK ORDER/MSA/PSA #> PREPARED FOR: METROPOLITAN SEWER DISTRICT OF GREATER CINCINNATI 1600 GEST STREET CINCINNATI, OH PREPARED BY: <COMPANY NAME, ADDRESS, PHONE, AND POINT OF CONTACT> <DATE>

128 TABLE OF CONTENTS Executive Summary 1. Data Evaluation 2. Model Source and Date Received 3. Validation Results 4. Conclusions

129 Executive Summary The Executive Summary shall present the following information: Brief project description MSD point-of-contact State that the MSDGC Guidelines and Standards were followed and when deviations occurred (if applicable) permission was given to deviate by the MSD PBD Modeling Group. Summary of the flow data used for the validation process State if the model is validated or not. If not, indicate the reason(s). This section is not to exceed one page

130 1. Data Evaluation This section shall present the following information: Indicate that you followed MSD s Modeling Guidelines and Standards. If you deviated from them, clearly indicate that and the name of the MSD PBD Modeling Group employee who gave you permission to deviate. A brief description and figure of the project area with the flow monitor location(s) and important assets associated with the project. Figure 1.1 is an example. Figure 1.1. <Project Title> A reference to the Rainfall and Rain Gauge Report(s) that were used. These reports can be provided by the MSD PBD Modeling Group

131 A reference the Flow Monitoring Quarterly Report(s) that were used. These reports can be provided by the MSD PBD Modeling Group. Dry-weather flow validation follow Modeling Standards and Guidelines, Section 7-3 A brief summary of storm events that were NOT used and the reason(s) for not using them. Indication of the storms that could have been used for the validation process. Indication of, per the MSDGC Modeling Guidelines and Standards, which 5 to 10 storms were chosen and the reason(s) for those choices. Summarize the storms that were chosen and summarize them using the Tables 1.1and 1.2 template. Refer to Appendix A which contains hydrographs and scatterplots of measured versus modeled volume, peak flow, and peak depth of the data from the 5-10 storms that were chosen for the validation process

132 Table 1.1 Wet Weather Events Used for Calibration Event Start Date & Time End Date & Time Duration (hrs) Total Rainfall (inch) Maximum 5-Min Intensity (in/hr) Table 1.2 Recurrence Interval Tables for Wet Weather Events 15-Min 1-Hour 6-Hour 24-Hour Event Peak Depth (inches) Recurrence Interval Peak Depth (inches) Recurrence Interval Peak Depth (inches) Recurrence Interval Peak Depth (inches) Recurrence Interval

133 2. Model Source and Date Received This section shall present the following information: Communication from the MSD PBD Modeling Group as to the last time the model was updated. Indicate the name of the MSD PBD Modeling Group employee who provided the model and the date it was provided. This shall be no longer than one paragraph. 3. Validation Results This section shall present the following information: Present the validation results for each location using the Table 3.2 and 3.3 templates. Highlight storms that were outside of the MSD Guidelines and Standards. Briefly comment on why you think the model did not validate. Some of the comments have been left in the table to assist the users of this template. Date Table 3.2 <Site Name> Flow Validation Peak Flow (mgd) Observed Modeled % Difference Observed Storm Volume (MG) Modeled % Difference

134 Date Table 3.3 <Site Name> Depth Validation Peak Depth (feet) Pipe Diameter: Observed Modeled Difference % Difference Refer to Appendix B for further data

135 4. Conclusions This section shall present the following information: Indication that the model was validated within MSD s Modeling Guidelines and Standards. If there were deviations from it indicate that and document that permission to deviate was given by the MSD PBD Modeling Group. Issues/concerns (if any) about the data used and/or the results. Recommendations (if any) for further work (i.e., more flow monitoring) to ensure the model is good enough for its intended purpose

136 APPENDIX A Flow Data Hydrographs and Scatterplots

137 APPENDIX B Validation Results

138 <PROJECT NAME> SYSTEM WIDE MODEL CALIBRATION REPORT CIP # < > <TASK ORDER/MSA/PSA #> PREPARED FOR: METROPOLITAN SEWER DISTRICT OF GREATER CINCINNATI 1600 GEST STREET CINCINNATI, OH PREPARED BY: <COMPANY NAME, ADDRESS, PHONE, AND POINT OF CONTACT> <DATE>

139 TABLE OF CONTENTS Executive Summary 1. Data Evaluation 2. Model Source and Date Received 3. Model Modifications 4. Calibration Results 5. Validation Results 6. Conclusions

140 Executive Summary The following information shall be presented in this section: Brief project description MSD point-of-contact State that the MSDGC Guidelines and Standards were followed and when deviations occurred (if applicable) permission was given to deviate by the MSD PBD Modeling Group. Calibration assessment State if the calibration standards were met. If not, indicate the reason(s). This section shall not to exceed one page

141 1. Data Evaluation This section shall present the following information: Indicate that you followed MSD s Modeling Guidelines and Standards. If you deviated from them, clearly indicate that and the name of the MSD PBD Modeling Group employee who gave you permission to deviate. A brief description and figure of the project area with the flow monitor location(s) and important assets associated with the project. Figure 1.1 is an example. Figure 1.1. <Project Title> A reference to the Rainfall and Rain Gauge Report(s) that were used. These reports can be provided by the MSD PBD Modeling Group