Watershed Modeling Some Simple Approaches New England Tribal NPS Workshop May 1, 2013

Transcription

1 Watershed Modeling Some Simple Approaches New England Tribal NPS Workshop May 1, 2013 Mark Voorhees US EPA New England

2 Today s Discussion Topics Some background on watershed modeling Models to be discussed Impervious Cover Model Simple Method Pollutant Load Export Rates from literature Derived Pollutant Load Export Rates using SCS Curve Number Model Load Duration Curves Best Management Practice Reductions 5/13/2013 2

3 Modeling Process Steps Step 1: Clearly define your purpose for using models? Step 2: Match the modeling approach(s) to fit your needs Always use the simplest modeling approach possible Step 3: Apply model or modeling approaches to your watershed Data compilation GIS analyses expedite process Selection of appropriate input values Spreadsheets are very useful 3

4 Usefulness of Simple Modeling Approaches Simple approaches are typically empirically derived and are excellent for demonstrating relative changes in watershed processes due land use activities Educational and informative to guide development of sound land use planning and development regulations Capable of quantifying the relative benefits of implementing controls or policies Great opportunity not to be missed 4

5 Quick background on some important processes to be aware of Hydrology Role of imperviousness Impervious Cover Model Regional rainfall patterns Pollutant processes build up and wash off erosion Water quality impacts Long term (e.g., habitat degradation, eutrophication) Short term (toxicity) 5

6 Hydrology and the developing watershed

7 Changes in Stream Hydrology as a Result of Urbanization Source: Schueler, 1994

8 Runoff Yield and Imperviousness Cover Stormwater runoff yield - million gallons/acre. USGS Lower Charles River Sub-watershed Flow Gauging Program Water Year 2000 Stormwater runoff yield (million gallons per acre) vs. percent effective impervious cover (Breault, et. Al, 2002) (Zarriello et al, 2002) Percent effective impervious 8

9 Effects of Urbanization on Maryland Stream Cross Section Source: Center for Watershed Protection, 2003

10 Consequently. Increased stormwater volume & velocity Stream widening & down cutting Decreased base flow And... more flooding! Changes to Stream Geomorphology

11 Center for Watershed Protection s Impervious Cover Model Source: Center for Watershed Protection, 2003 Source: Center for Watershed Protection, 2003

12 New England Region Rainfall Patterns Important Points Most rain events are small in size; Occur regularly (average about once every three days) The total volume and event size distribution are relatively consistent across New England Region 12

13 Precipitation Analysis

14 Percentage of Total Number of Rainfall Events Based on Size of Rain Events - Boston, MA ( ) inches 2% inches 5% inches 10% inches 27% 2.0 inches and above 1% inches 55% inches inches inches inches inches 2.0 inches and above

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16 Pollutants Trash Heavy Metals Nutrients Pathogens Sediment Oil & Grease

17 Today s Discussion of Pollutants Nutrients Phosphorus and Nitrogen Trace metals Zinc as an example Solids However, methodologies are suitable to many other pollutants 17

18 Stormwater Pollutants and Urban Runoff Nitrogen N Oxides are readily washed off in early portion of rain events (first flush is typical). Organic nitrogen can be a significant part of N load High removals of SW nitrogen may require de-nitrification Phosphorus Mostly associated with very fine particles ~ 40 microns Washed from impervious surfaces with small amounts of rainfall (0.3 inches) Stormwater controls must have filtration component to be effective Trace Metals (e.g., Zinc) Highly associated with particulate matter Many are readily washed off of impervious surfaces High reductions can be achieved through settling practices.

19 Sources of Phosphorus & Nitrogen in SW

20 Solids and nutrients from Agricultural Sources Source: 20

21 The Simple Method Calculating storm water pollutant loading from developed lands Use: Estimate stormwater runoff pollutant loads for urban areas Information needed for the Simple Method: Sub watershed drainage area; fraction impervious cover; runoff pollutant concentrations; and annual precipitation t/simple%20meth/simple.htm 21

22 Simple Method Notes and Limitations Suitable for providing general planning level estimates of likely stormwater pollutant export from areas at the scale of a development site or sub watershed (areas for which base flow is nonexistent or very small) Most appropriate for assessing and comparing the relative stormwater pollutant load changes of different land use and development scenarios 22

23 The Simple Method The Simple Method estimates pollutant loads for chemical constituents as a product of annual runoff volume and pollutant concentration, as: L = * R * C * A Where: L = Annual load (lbs) R = Annual runoff (inches) C = Pollutant concentration (mg/l) A = Area (acres) = Unit conversion factor 23

24 Simple Method Runoff Volume The Simple Method calculates annual runoff as a product of annual runoff volume, and a runoff coefficient (Rv). Runoff volume is calculated as: R = P * P j * Rv Where: R = Annual runoff (inches) P = Annual rainfall (inches) P j = Fraction of annual rainfall events that produce runoff (usually 0.9) Rv = Runoff coefficient 24

25 Simple Method Runoff Coefficient In the Simple Method, the runoff coefficient is calculated based on impervious cover in the subwatershed The following equation represents the best fit line for the dataset (N=47, R 2 =0.71). Rv= Ia; Where: Ia = Impervious fraction 5/13/

26 Typical Percent Impervious Values for the Simple Method Density Table 5. Impervious Cover (%) for Various Land Uses Source Land Use Low Density Residential Medium Density Residential (dwelling NRCS units/acre) Northern Puget Sound Virginia (NVPDC, 1980) 1 Olympia (COPWD, 1995) (Aqua Terra, 1994) (USDA, 1986) < Rouge River (Kluitenberg, 1994) 19 Model Default High Density Residential Multifamily Townhouse (>7) Industrial Commercial Roadway 80 1: NVPDC data measure effective impervious cover (i.e., rooftops are not included in residential data) 2: Model default values are approximately equal to the median of Olympia, Puget Sound, NRCS, and Rouge River data, with adjustments made where studies estimate impervious cover for a broad range of densities. 5/13/ t/simple%20meth/simple.htm 26

27 Simple Method Default Concentrations (see link below for possible defaults for TP and TN) Table 1: Pollutant Concentrations by Land Use: Total Suspended Solids (mg/l) Land Use Source Residential Commercial Roadway Industrial Notes Schueler, 1987 mean This value reflects an estimate based on 25 data points from a wide range of watershed sizes. Data reflect instream concentrations. A small watershed size (i.e., 10 acres) was assumed to minimize the influence of the channel erosion component. Gibb et al., 1991 mean These values represent recommended estimates for planning purposes and are based on an analysis of mean concentrations from over 13 studies from the US and British Columbia. Smullen and Cave, 1998 median This study probably represents the most comprehensive data set, with 3,047 event samples being included from across the nation. Data includes pooled NURP, USGS, and NPDES sources. The value is a median of EMCs and applies to general urban runoff (i.e., mixed land uses). The low concentration relative to other data can be attributed to the fact that, while NURP data represent small watersheds where channel erosion may play a role, NPDES data are collected as "end of the pipe" concentrations for very small drainage areas of a uniform land use. The NPDES concentrations were approximately 70% lower than concentrations from NURP or USGS. US EPA, 1983 median Claytor and Schueler, Barrett and Malina, Caraco and Schueler (1999). Arid Climates Driscoll, Shelley and Gaboury, Whalen and Cullum, These values represent NURP data for residential and commercial land use. NURP data were collected in the early 1980s in over 28 different metropolitan areas across the US. The roadway value is the un-weighted mean of 8 studies conducted by the FHWA. The industrial value is the mean value from 6 storms monitored at a heavy industrial site in Auckland, NZ. This data reflects a study of vegetative swales treating highway runoff in Austin, TX. Value represents average of the mean inflow concentrations measured at 2 sites. Data were collected over 34 storm events. This value represents an average of EMC data collected from 3 arid climate locales (Phoenix, Boise, and Denver). A total of 90 data points are used, with each site having at least 16 data points. Value applies to general urban runoff (i.e., mixed land uses). This value is the average of 4 median EMCs collected from highway sites in Nashville, Denver, Milwaukee, and Harrisburg. A total of 93 data points were used to develop value, with each site having at least 16 data points. This value is the median value of 8 highway studies from across the US. Some of the data from the Driscoll study (1986) is included. These data are from an assessment of urban runoff quality that looked at NURP and State of Florida data. The NURP data are presented. Residential and commercial values are mean values for specified land uses and reflect between 200 and 1,100 sampling events depending on the parameter and land use. Industrial values are from 4 NURP sites and generally represent light industrial land use. Model Default Value : Concentration based on a 10-acre drainage area The model default values represent best professional judgment, and give additional weight to studies conducted at a national level. Data do not incorporate studies on arid climates. 5/13/ t/simple%20meth/simple.htm 27

28 An example using the Simple Method Situation: A residential development is proposed for a sub watershed area within the Lake Bubaboo watershed. The project is proposed for a 35 acre area that is currently mostly forested. The LBA is concerned about increased phosphorus loading to the lake and is insisting that the project include an adequate level of stormwater control so that there will be no increase in annual phosphorus load to the lake. Question: What would be the minimum percent reduction in annual phosphorus load that the proposed project s stormwater management program would need to achieve in order to meet the LBA s request? 28

29 Example Project Information Area = 35 acres Annual precipitation = 43.5 inches Existing conditions: Fraction imperviousness of forested sub watershed = 0.06 (i.e., 6% paved roadway through sub catchment) Typical median stormwater TP concentration (C) for forested area = 0.10 mg/l Proposed conditions: Fraction imperviousness of proposed residential development = 0.25 Typical median stormwater TP concentration (C) for residential area = 0.26 mg/l 5/13/

30 Example Calculations (continued) Step 1: Calculate annual runoff volume for existing and proposed conditions using: R = P x P j x Rv Where: R = Annual runoff (inches) P = Annual rainfall (inches) = 43.5 inches P j = Fraction of annual rainfall events that produce runoff =0.9 Rv = Runoff coefficient (where Rv = Ia) Ia = Impervious fraction Existing Conditions: R=43.5 x 0.9 x ( (0.9 x 0.06)) = 4.1 inches Proposed Conditions: R=43.5 x 0.9 x ( (0.9 x 0.25))= 10.8 inches 5/13/

31 Example Calculations (continued) Step 2: Calculate annual phosphorus load for existing and proposed conditions using: L = * R * C * A Where: L = Annual load (lbs) R = Annual runoff (inches) C = Pollutant concentration (mg/l) A = Area (acres) = Unit conversion factor Existing Conditions: L Exist =0.226 x 4.1 inches x 0.10 mg/l x 35 acres = 3.2 lbs P Proposed Conditions: L Prop =0.226 x 10.8 inches x 0.26 mg/l x 35 acres = 22.2 lbs P 5/13/

32 Example Calculations (continued) Step 3: Calculate minimum percent reduction needed by proposed project s stormwater management plan using: % Reduction = [ (L Prop L Exist )/L Prop ]x 100 = [ ( )/22.2]x 100 = 86% 5/13/

33 Example of Annual Phosphorus Load Export Rates using the Simple Method Typical land use associated with percent impervious values (1) Rural residential Large lot single family Medium to high density residential Multi family residential Percent Impervious (%) Annual Phosphorus load export rate developed from the Simple Method (Schueler 1987) (lbs/acre yr) TP EMC=0.22 mg/l TP EMC=0.26 mg/l TP EMC=0.30 mg/l Light commercial/industr ial Heavy commercial Annual rainfall for Boston 43.5 inches used to calculate export rates 5/13/

34 Unit Area Loading or Pollutant Load Export Rate Method This method uses published yield values to estimate annual average pollutant loading for a specific land use Simple straight forward approach works well with spreadsheets and information from GIS watershed data layers Information needed: Inventory of watershed areas by land use Reported pollutant load export rates (e.g., literature, TMDLs and watershed loading analyses) 5/13/

35 Unit Area Loading Method Method: Multiply area of land use by the unit area export rate for the pollutant of interest; Usefulness and limitations: This method is useful for estimating the relative magnitude of runoff pollutant loading from various land use based sources in a watershed; This method is least likely to give accurate results because of the uncertainty of fit between the catchment of interest and the data collection location(s); 5/13/

36 Some Literature derived Runoff Pollutant Load Export Rates Table 3 12: Typical Pollutant Loadings (Ibs/acre yr) From Different Land Uses ( Taken from Fundamentals of Urban Runoff Management: Technical and Institutional Issues. 2nd Edition, 2007 By: Earl Shaver, Richard Horner, Joseph Skupien, Chris May, Graeme Ridley) Land Use TSS TP TKN NH 3 N NO 2 &NO 3 BOD COD Pb Zn Cu Cd Commercial Parking Lot High Density Residential Medium Density Residential Low Density Residential Highway n/a n/a Industrial n/a n/a Shopping Center n/a n/a Source: Based on Table 2.5 in Burton and Pitt, ccp2/id/1999/rec/4 36

37 Example Calculation using Pollutant Load Export Rates Estimate the annual total nitrogen (TN) load that discharges from storm drain 1 (SD1) to Calvin Bay. Step 1. A delineation of the contributing drainage area to SD1 using storm drainage maps and the land use data layer in GIS indicates the following inventory: 11.5 aces commercial 4.7 acres high density residential (HDR) ; and 3.1 acres of parking lots 37

38 Example Calculation using Pollutant Load Export Rates (continued) Step 2: Select appropriate load export rates (LER). Table 3.12 does not provide rates for TN but does for TKN and NO 2 & NO 3 (TN = TKN + NO 2 & NO 3 ) Commercial: TN LER = = 9.6 lbs/ac/yr HDR: TN LER = = 8.0 lbs/ac/yr Parking Lot: TN LER = = 6.2 lbs/ac/yr Table 3 12: Typical Pollutant Loadings (Ibs/acre yr) From Different Land Uses ( Taken from Fundamentals of Urban Runoff Management: Technical and Institutional Issues. 2nd Edition, 2007 By: Earl Shaver, Richard Horner, Joseph Skupien, Chris May, Graeme Ridley) Land Use TSS TP TKN NH 3 N NO 2 &NO 3 BOD COD Pb Zn Cu Cd Commercial Parking Lot High Density Residential Medium Density Residential Low Density Residential Highway n/a n/a Industrial n/a n/a Shopping Center n/a n/a Source: Based on Table 2.5 in Burton and Pitt,

39 Example Calculation using Pollutant Load Export Rates (continued) Step 3: Calculate TN loads for each land use area: Commercial: 9.6 lbs/ac/yr x 11.5 acres = lb/yr HDR: 8.0 lbs/ac/yr x 4.7 acres = 37.6 lb/yr Parking Lot: lbs/ac/yr x 3.1 acres = 19.2 lb/yr Step 4: Sum TN Loads: SD1 TN load = = lb/yr 39

40 Suggested Phosphorus Load Export Rates when percent imperviousness is unknown Annual Phosphorus Load Export Rates by Land Use when Percent imperviousness is unknown Land use (source) TP load export rate (lb/ac/yr) Agriculture general*(1) 0.45 Commercial **(2) 1.50 Forest (3) 0.12 Freeway (2) 0.80 High density residential (2) 1.00 Industrial (2) 1.30 Medium density residential (2) 0.50 Low density residential (rural) (3) 0.27 Open space (3) 0.27 Sources: (1) Budd and Meals 1994; (2) Shaver et al. 2007; (3) Mattson and Isaac 1999 * Agriculture includes row crops, actively managed hay fields and pasture land. ** Institutional type land uses such as government properties, hospitals, and schools are included in the commercial land use category for the purpose of calculating phosphorus loadings. 40

41 Suggested Phosphorus Load Export Rates when Imperviousness is known Table 1. Proposed Phosphorus Load Export Rates (PLER) for various stormwater runoff source categories Phosphorus Source Category by Land Phosphorus Load Export Land Surface Cover Comments Use Rate, Kg/ha/yr Commercial (Com) and Industrial (Ind) Multi Family (MFR) and High Density Residential (HDR) Medium Density Residential (MDR) Low Density Residential (LDR) "Rural" Highway (HWY) Forest (For) Agriculture (Ag) *Developed Land Pervious (DevPERV) Hydrologic Soil Group A/B *Developed Land Pervious (DevPERV) Hydrologic Soil Group C *Developed Land Pervious (DevPERV) Hydrologic Soil Group D Impervious 2.0 Derived using a combination of the Lower Charles USGS Loads study and NSWQ dataset. This PLER is approximately 75% of the HDR PLER and reflects the difference in the distributions of SW TP EMCs between Commercial/ Industrial and Residential. Pervious See* DevPERV Impervious 2.6 Largely based on loading information from Charles USGS loads, SWMM HRU modeling, and NSWQ data set Pervious See* DevPERV Impervious 2.2 Largely based on loading information from Charles USGS loads, SWMM HRU modeling, and NSWQ data set Pervious See* DevPERV Impervious 1.0 Derived from Mattson Issac and subsequent modeling by Tetra Tech Pervious 0.2 for Optimization study (composite rate 0.3 kg/ha/yr) Impervious 1.5 Derived from Shaver et al and subsequent modeling by Tetra Tech for Optimization study (composite rate 0.9 kg/ha/yr) Pervious See* DevPERV Impervious 1.0 Derived from Mattson Issac and subsequent modeling by Tetra Tech Pervious 0.1 for Optimization study (composite rate 0.13 kg/ha/yr) Cover Crop/Grazing 0.8 Table C 4 of NH Lake TMDL Reports (Cited source: Reckhow et al. Row Crop ) Hayland no manure 0.4 Pervious 0.2 Pervious 0.5 Pervious 0.8 Derived from SWMM HRU modeling with assumed representative TP concentration of 0.3 mg/l for pervious runoff from developed lands. TP of 0.3 mg/l is based on NSWQ dataset, TB 9 (CSN, 2011), and other PLER literature. 41 Source of Table : See Attachment 1 to Appendix F to 2013 Draft New Hampshire Small MS4 General Permit: F Small MS4 NH.pdf

42 Model Simulated Pollutant load Export Rates Using the Curve Number Method EPA used P8 model to simulated average annual runoff yields for a variety of pervious surfaces (e.g., million gallons/acre/year) P8 model is a continuous simulation model that uses hourly rainfall data to generate runoff volumes for a long term period (e.g., 10 years) P8 uses the Curve Number method to estimate runoff volumes from pervious surfaces The Curve Number method was developed by SCS (now NRCS) and is a commonly and widely used empirical model suitable for many land 42 covers including agriculture

43 Model Simulated Pollutant load Export Rates Using the Curve Number Method Average annual pollutant load export rates can be calculated using the model simulated runoff yields multiplied by a pollutant concentration (or a range of concentrations) The runoff yields reflect regional climatic patterns; This method allows the user to estimate annual loadings that reflect regional climatic conditions and the users choice for quality P8 Model Simulated Average Annual Runoff Yield Using the Curve Number Method ( Boston MA, Hourly rainfall ), MG/acre/yr 0.80 Average Annual Runoff Yield, Million gallons/acre/year Curve Number 43

44 Curve Number Method and Model Derived Export Rates The Curve Number method is widely used in the design of stormwater controls Commonly used for agricultural sources Use of the derived export rates based on annual runoff yield is useful for planning purposes and estimating relative differences among source categories and relative benefits of management options. 44

45 Curve Number Method to Generate Generic Runoff Flow and Load Export Rates For New England 45

46 Curve Numbers by Land Cover and Hydrologic Soil Group United States Department of Agriculture Natural Resources Conservation Service Part 630 Hydrology National Engineering Handbook Chapter 9 Hydrologic Soil-Cover Complexes For a more complete list of curve numbers see the above document found at this link: aspx?content=17758.wba Hydrologic Soils are identified in soil surveys Pervious area HSG A Pervious area HSG B Pervious area HSG C Pervious area HSG D well drained soils moderately drained soils limited permeability poorly drained soils Runoff Curve Numbers The specified SCS Curve Number (CN) reflects an areaweighted average of the pervious areas, which generally reflect land cover and soil hydrologic group. The following table lists typical CN values as a function of land use, hydrologic condition, and soil group: Land Use Grassed Areas Curve Number by Hydrological Soil Group Hydrologic Condition A B C D Good (>75% Cover) Fair Poor (<50% Cover) Meadow / Idle Good Woods Good (thick forest) Fair Poor (thin, no mulch) Construction Site Newly Graded Impervious

47 Tabulated Model Calculated Annual Export Rates Spreadsheet generated tables of export rates for various curve numbers and pollutant concentrations Export rate = runoff yield (MG/ac/yr) x concentration (mg/l) x x 10 6 L/MG x 1 lb/454,000 mg P8 model simulations Runoff Boston, MA hourly yield, precipitation, 1998 MG/acre/yr 2002 curve number Annual Phosphorus Load Export Rate lb/acre/yr Average Annual Flow Weighted Total Phosphorus Concentration, mg/l % by P MG = million gallons, Average annual rainfall = 43.5 inches 47

48 Tabulated Model Calculated Annual Export Rates P8 model simulations Boston, MA hourly precipitation, curve number Runoff yield, MG/acre/yr Annual Nitrogen Load Export Rate lb/acre/yr Average Annual Flow Weighted Total Nitrogen Concentration, mg/l % by P MG = million gallons, Average annual rainfall = 43.5 inches P8 model simulations Runoff Annual Total Suspended Solids Load Export Rate lb/acre/yr Boston, MA hourly yield, Average Annual Flow Weighted Total Suspended Solids Concentration, mg/l precipitation, 1998 MG/acre/yr % by P MG = million gallons, Average annual rainfall = 43.5 inches curve number

49 Example Calculation using Model Generated Export Rates Estimate the annual TSS load from a 10 acre pasture with HSG C in fair hydrologic condition. Assume a median TSS concentrations of 70 mg/l The Curve number is 79 Using the export rate table, the annual runoff yields for CNs 70 and 80 are and MG/acre/yr, respectively. Interpolating, the runoff yield for CN 79 is MG/acre/yr The export rate for CN 79 and TSS conc. of 70 mg/l = 0.150(MG/ac/yr) x 70 (mg/l) x x 10 6 L/MG x 1 lb/454,000 mg = 88 lbs/ac/yr The estimated annual TSS load from the pasture = 10 acres x 88 lb/acre/yr= 880 lbs yr Runoff Curve Numbers The specified SCS Curve Number (CN) reflects an areaweighted average of the pervious areas, which generally reflect land cover and soil hydrologic group. The following table lists typical CN values as a function of land use, hydrologic condition, and soil group: Land Use Grassed Areas Curve Number by Hydrological Soil Group Hydrologic Condition A B C D Good (>75% Cover) Fair Poor (<50% Cover) Meadow / Idle Good Woods Good (thick forest) Fair Poor (thin, no mulch) Construction Site Newly Graded Impervious

50 Pollutant Load Duration Curves 50

51 Flow & Fecal Load Duration Curves 51

52 Load Duration Curves Flow Duration Curve Load Duration Curves Data intensive (not really a simple approach): need long term flow record or a calibrated continuous simulation hydrologic model Abundant water quality data and/or calibrated watershed water quality model Useful for understanding the nature of contributing sources and for which management activities are needed dry weather (low flow) & wet weather (high flow) 08_23_tmdl_duration_curve_guide_aug2007.pdf 52

53 Develop estimates of long term cumulative performance using regional climate data Reduction Credits for Structural Controls Stormwater Best Management Practices Performance Analysis by Tetra Tech Inc. Develop and calibrate models to performance data Simulate long term performance varying the capacity of controls Validate results with literature review Charles River Stormwater BMP

54 BMP Performance Curve Concept Size BMPs from established curves developed from calibrated models and detailed performance data Provides long term cumulative performance estimates based on BMP design capacity Eliminates the need for detailed modeling and evaluation in individual applications Percentage removal for TSS 90% 80% 70% 60% 50% 40% 30% 20% 10% 40% 0.65 in 0.90 in BMP I BMP II 0% BMP size (controlled depth of runoff)

55 Scheme for BMP Performance Curve Development Precipitation Land simulation (SWMM) Surface runoff generation and pollutant wash off BMP Performance Curve: Gravel Wetland Land Use: Commercial Pollutant Removal 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% BMP simulation (SUSTAIN/BMPDSS) BMP Treatment 0% Depth of Runoff Treated (inches) TSS TP Zn

56 Generation of BMP Performance Curves for New England Region BMPs 100% BMP Performance Curve: Infiltration Trench Land Use: Commercial (Soil infiltration rate 0.17 in/hr) 100% 90% 90% Surface Infiltration (6 infiltration rates) Pollutant Removal 80% 70% 60% 50% 40% 30% 20% 80% 70% 60% 50% 40% 30% 20% Runoff Volume Reduction 10% 10% 0% 0% Depth of Runoff Treated (inches) Infiltration trenches (6 infiltration rates) 100% 90% 80% TSS TP Zn Volume BMP Performance Curve: Biorentention Land Use: Commercial Bio-filtration Pollutant Removal 70% 60% 50% 40% 30% 20% 10% 0% Depth of Runoff Treated (inches) Porous pavement with underdrain 100% 90% TSS TP Zn BMP Performance Curve: Gravel Wetland Land Use: Commercial WQ Swales (non-infiltration) Gravel wetland Enhanced Bio-retention* * Optimized for N and P removal Curves not yet final Pollutant Removal 80% 70% 60% 50% 40% 30% 20% 10% 0% Depth of Runoff Treated (inches) TSS TP Zn

57 BMP Performance Extrapolation Tool (BMP PET)

58 Questions? Thank you Mark Voorhees US EPA (OEP06 4)

59 Additional reference and information sources USGS National Map: (Data include: Elevation, Orthoimagery, Hydrography, Geographic Names, Boundaries, Transportation, Structures, and Land Cover, while products include: US Topo and Historical Topo Maps. The National Map Viewer also allows visualization and identification queries (but not downloads) of Other Featured Data, to include Ecosystems, Protected Areas, Gap Analysis Program Land Cover, Hazards, Weather, Wetlands, Public Land Survey System, and National Park Service Boundaries.) You can find Soil Data here: 59

60 Report on the development of Stormwater BMP Performance Curves for New England Region (Tetra Tech, Inc., 2010). dfs/bmp Performance Analysis Report.pdf Spreadsheet tool for using the curves and instructions. ces.html 60

61 Upcoming EPA tool : To be released later this month). It will be available on this page: er models data tools.htm. Also, check out Watershed Assessment, Tracking & Environmental Results Tool (WATERS) (under Watershed Tools).