Western Washington Hydrology Model (WWHM) Software Introduction. Doug Beyerlein, P.E., P.H., D.WRE Clear Creek Solutions, Inc. Mill Creek, Washington

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1 Western Washington Hydrology Model (WWHM) Software Introduction Doug Beyerlein, P.E., P.H., D.WRE Clear Creek Solutions, Inc. Mill Creek, Washington

2 Clear Creek Solutions Hydrology Expertise Clear Creek Solutions, Inc., provides complete range of hydrologic and stormwater modeling services. Clear Creek specializes in continuous simulation hydrologic modeling. We have 40+ years of experience modeling complex hydrologic and stormwater problems. We originally created WWHM for Washington State Department of Ecology and have adapted it to model other metropolitan areas throughout the United States. We teach WWHM and HSPF workshops.

3 Presentation Introduction WWHM and NPDES MS4 Requirements WWHM s HSPF Computational Engine WWHM Capabilities WWHM Sample Application WWHM LID Options Questions & Answers

4 Introduction WWHM was originally developed for and funded by the Washington State Department of Ecology. WWHM versions: WWHM2012*: 19 counties of Western Washington BAHM*: San Francisco Bay Area (Alameda, Santa Clara, San Mateo counties, CA) SDHM*: San Diego County, CA SOHM*: Orange County, CA SMRHM*: Riverside County, CA SAHM*: Sacramento County, CA SalinasHM*: City of Salinas, CA TRUST*: Tualatin Basin (Washington County), OR WWHM4: entire United States (lower 48 states) *free software

5 WWHM and NPDES MS4 NPDES MS4 permit requirements from the federal Clean Water Act limit the change in streamflow due to changes in land use.

6 WWHM and NPDES MS4 NPDES MS4 = National Pollution Discharge Elimination System Municipal Separated Storm Sewer System.

7 WWHM and NPDES MS4 NPDES MS4 permit requirements are specified in the Department of Ecology s 2012 Stormwater Management Manual for Western Washington.

8 WWHM and NPDES MS4 There are 9 minimum requirements for NPDES Phase I and Phase II communities for new land use development and redevelopment.

9 WWHM and NPDES MS4 Modeled by WWHM2012: Minimum Requirement #5: On-site Stormwater Management (LID requirement). Minimum Requirement #6: Runoff Treatment (Water Quality) Minimum Requirement #7: Flow Control Minimum Requirement #8: Wetland Inflow Volume

10 WWHM and NPDES MS4 Stormwater runoff increases whenever it rains due to land use changes.

11 WWHM and NPDES MS4 Distribution of Seattle annual rainfall and runoff: Blue: Evapotranspiration Green: Groundwater Yellow: Interflow Red: Surface Runoff Forest Lawn Impervious

12 WWHM and NPDES MS4 Increases in stormwater runoff produces higher peak flows and more stream bank and channel erosion.

13 WWHM and NPDES MS4 Stream bank and channel erosion can be prevented by adding stormwater mitigation procedures and facilities (ponds, permeable pavement, bioretention, etc).

14 WWHM and NPDES MS4 Stormwater mitigation facilities are sized so that they prevent an increase in the number and size of erosive flows.

15 WWHM and NPDES MS4 Hydrologic computer stormwater modeling is used to determine whether or not proposed mitigation measures prevent an increase in the number and size of erosive flows with changes in land use.

16 WWHM and NPDES MS4 In the 19 counties of Western Washington erosive flows occur when streamflow is between 50% of the 2-year flow and 100% of the 50-year flow.

17 WWHM and NPDES MS4 Flow Duration Analysis: Percent of time the flow exceeds a specific value. Continuous simulation hydrology is needed to compute flow duration.

18 WWHM and NPDES MS4 Continuous simulation hydrology models the entire hydrologic cycle for multiple years. WWHM is a continuous simulation hydrology model that calculates the stormwater runoff used for the flow duration analysis.

19 WWHM s HSPF Computation Engine WWHM includes HSPF to do the continuous simulation hydrology computations. HSPF runs in the background with calibrated parameter values and local meteorological data. HSPF is sponsored and funded by US EPA and USGS. HSPF is available free on the Internet.

20 WWHM s HSPF Computation Engine HSPF: Hydrologic Simulation Program FORTRAN History: 1966 Stanford Watershed Model by Linsley and Crawford 1972 HSP by Hydrocomp (Palo Alto, CA) 1973 ARM (Agricultural Runoff Management) Model for EPA by Hydrocomp 1974 NPS (Non-Point Source) Model for EPA by Hydrocomp 1979 HSPF (combining HSP, ARM, and NPS) for EPA by Hydrocomp

21 WWHM s HSPF Computation Engine The entire water cycle is modeled on an hourly or shorter time step for multiple years. The model computes changes in soil moisture, evapotranspiration, and runoff every time step. HSPF calculates 3 types of runoff: surface runoff (mostly from impervious surfaces) interflow (shallow subsurface runoff) groundwater/base flow (dry weather flows)

22 WWHM Capabilities WWHM uses HSPF continuous simulation hydrology to compute stormwater runoff for both predevelopment and post-development conditions. Predevelopment Post-development

23 WWHM Capabilities WWHM includes a map of each of the 19 counties of Western Washington.

24 WWHM Capabilities King County s rainfall stations: SeaTac Airport Landsburg Each county includes one or more rainfall stations.

25 WWHM Capabilities The user represents their project area with elements representing land use info and stormwater mitigation facilities: land use basins stormwater ponds and vaults water quality facilities low impact development (LID) facilities commercial stormwater solutions* * Currently not available in the standard Ecology version of WWHM2012.

26 WWHM Capabilities The user creates a schematic of the land use basins, flow paths, and mitigation facilities. HSPF uses this schematic diagram to compute and route the stormwater runoff.

27 WWHM Capabilities WWHM statistical tools includes flow duration analysis. This flow duration plot shows that the mitigated (red) erosive flows are less than or equal to the pre-development (blue) erosive flows and meets flow control requirements (MR #7).

28 WWHM Capabilities WWHM statistical tools includes plotting options. This plot shows wet-dry seasonal cycles of runoff.

29 WWHM Sample Application Example: Convert undeveloped land to suburban residential housing.

30 WWHM Sample Application User selects land development location and places red dot on county map.

31 WWHM Sample Application User inputs pre- and post-development land use. Pre: forest Post: lawn, roof, road, parking, sidewalk, driveways, & pond

32 WWHM Sample Application User inputs initial pond specifications or uses AutoPond to optimize pond size.

33 WWHM Sample Application WWHM compares predevelopment and post-development routed runoff statistics. WWHM flow frequency computes 2-, 5-, 10-, 25-, 50- and 100-year flows:

34 WWHM Sample Application WWHM compares predevelopment and post-development routed runoff statistics. Flow duration for flow control (50% of 2-year to 100% of 50-year):

35 WWHM Sample Application WWHM computes runoff treatment (water quality) requirements:

36 WWHM Sample Application WWHM output summarizes statistics and whether or not the facility meets the jurisdiction s stormwater standards:

37 WWHM Sample Application User outputs report file and project file. Output files can be submitted to the permitting agency for approval. Permitting agency can load project file and rerun analysis, if needed. Report file summarizes input data and output results.

38 WWHM Sample Application Guidance/help is provided by: WWHM User Manual Training workshops CCS tech on-line and phone support

39 WWHM LID Options Green/vegetated/eco-roofs Permeable/porous pavement Bioretention/rain gardens Modular Wetland commercial products

40 WWHM LID Options LID uses long-term on-site infiltration and evapotranspiration to reduce total stormwater runoff volume. What happens between storm events is often more important than what happens during storm events.

41 WWHM LID Options Ecology s new LID requirement: Minimum Requirement #5: On-site Stormwater Management. Projects shall employ On-site Stormwater Management BMPs in accordance with the following projects thresholds, standards, and lists to infiltrate, disperse, and retain stormwater runoff on-site to the extent feasible without causing flooding or erosion impacts (Ecology, 2012 SWMMWW, Volume 1, p. 2-28).

42 WWHM LID Options Ecology s new LID requirement: Minimum Requirement #5: On-site Stormwater Management. New LID duration standard: 8% of the 2-yr flow to 50% of the 2-yr flow.

43 WWHM LID Options WWHM includes the following LID options: Green/vegetated/eco-roofs to retain rainfall and increase evapotranspiration and reduce stormwater runoff. Permeable/porous pavement to infiltrate rainfall and reduce stormwater runoff. Bioretention/rain gardens/cavfs (Compost Amended Vegetated Filter Strips) to retain and infiltrate water and reduce runoff. Commercial bioretention units* to retain and infiltrate water and reduce runoff. * Represented by the generic bioretention element or SSD element in WWHM2012.

44 WWHM LID Options Green roof element: increases evapotranspiration.

45 WWHM LID Options Permeable pavement element: increases infiltration.

46 WWHM LID Options Evaporation from pavement Rain on pavement Surface Runoff Infiltration through pavement Underdrain Flow Infiltration to gravel subgrade Infiltration to native soil Permeable pavement flow paths

47 Bioretention element: WWHM LID Options increases evapotranspiration and infiltration.

48 WWHM LID Options Ecology SWMMWW Definitions: Bioretention Engineered facilities that treat stormwater by passing it through a specified soil profile, and either retain or detain the treated stormwater for flow attenuation. Refer to Chapter 7 of Volume V for Bioretention BMP types and design specifications. Rain Garden A non-engineered, shallow, landscaped depression, with compost-amended native soils or imported soils, and adapted plants. The depression is designed to pond and temporarily store stormwater runoff from adjacent areas, and to allow stormwater to pass through the amended soil profile. Refer to the Rain Garden Handbook for Western Washington Homeowners (WSU, 2007 or as revised) for rain garden specifications and construction guidance.

49 WWHM LID Options Evapotranspiration Rain Surface Runoff Surface ponding Infiltration through top layer Infiltration through second layer Underdrain Flow Infiltration through third layer Bioretention flow paths Infiltration to native soil

50 WWHM LID Options Commercial solutions like Modular Wetlands and StormTrap products can be modeled.

51 WWHM LID Options Commercial solutions: Modular Wetlands Interim solution: use SSD (Stage-Storage-Discharge) element with Modular Wetlands specific dimensions.

52 WWHM LID Options For StormTrap products use the SSD Table element (Stage- Storage-Discharge Table) to represent the product.

53 Questions??? Clear Creek Solutions, Inc. Doug Beyerlein, P.E Joe Brascher