The Use of WinSLAMM in the Selection, Design and Placement of Stormwater BMPs. Stephen J. Souza, Ph.D. Jacob E. Helminiak, P.E. Princeton Hydro, LLC

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1 The Use of WinSLAMM in the Selection, Design and Placement of Stormwater BMPs Stephen J. Souza, Ph.D. Jacob E. Helminiak, P.E. Princeton Hydro, LLC 1108 Old York Rd., Ringoes, NJ

2 The Relationship of Watershed Development and Stormwater Need to assess and untangle these relationships in order to develop and implement cost-effective restoration solutions Increased impervious Increase in runoff volume and flow Decreased baseflow Increased pollutant loading Ecosystem degradation Modeling aids these types of assessments

3 Mitigation of Stormwater Impacts Requires integration of hydrologic, hydraulic, water quality and ecological solutions Proper design starts with the accurate understanding of the problem s magnitude Solutions will achieve desired result(s) only if properly sized and located Need means to measure success

4 Why Model In most cases modeling can be used to evaluate a wider array of conditions than is possible through field based techniques alone Quicker Cost effective Generates an expanded data set Allows analysis of present and future conditions Can be used to project or quantify success

5 Modeling to Evaluate Solutions What types of BMPs should be used? Structural Non-structural Maintenance (e.g., street sweeping) Where should the BMP be located? How frequently will it need to be maintained? What are the expected removal efficiencies? What is the projected water quality benefit?

6 WinSLAMM (Source Loading And Management Model for Windows)

7 Model Background and Typical Uses Initially created to more efficiently evaluate stormwater control practices (BMPs), now includes a variety of source area and end-of-pipe controls Developed primarily as a planning level tool, generating information needed to make planning level decisions, while not generating or requiring superfluous information Designed to give relatively simple answers (pollutant mass discharges and control measure effects for a variety of potential conditions)

8 Model Background and Typical Uses Predicts the concentrations and loadings of many different pollutants from a large number of potential source areas Calculates flow and pollutant discharges that reflect a broad variety of development conditions and the use of many combinations of common urban runoff control practices

9 Model Background and Typical Uses Event Based Model Calculates mass balances for both particulate and dissolved pollutants and runoff flow volumes for different development characteristics and rainfalls Predicts the relative contributions of different source areas (roofs, streets, parking areas, landscaped areas, undeveloped areas, etc.) for each land use investigated Without calibrated data, model results (particulate and pollutant loadings) should be considered relative, not absolute

10 Input Parameters Rainfall Pollutant Data Land Use Data Optional BMPs Existing Proposed Output Runoff Pollutant Loading

11 Input Parameters

12 Rainfall 67 available data sets Each contains numerous rain events Custom rainfall

13 Runoff Coefficient

14 Runoff Coefficient Contain volumetric runoff coefficients for different source areas for different rain depths Based on substantial field monitoring in the upper Midwest, the Southeast, and Ontario Verified in many other locations in the US Can be changed to reflect observed local conditions

15 Pollutant Input Parameters

16 Pollutant Input Parameters Specify pollutants of concern Particulate, Dissolved, Total Pollutant Probability Distribution (means, variability) Particulate Solids Concentration Based on substantial field investigation

17 Land Use and Source Areas Six Land Use Categories: Residential Institutional Commercial Industrial Open Space Freeways Many source area options within each Define entire subwatershed Define drainage system

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19 Input Parameters Rainfall Pollutant Data Land Use Data Optional BMPs Existing Proposed Output Runoff Pollutant Loading

20 Control Practices (BMPs) Source Controls Outfall Controls Control practices (BMPs) include: detention ponds, infiltration devices, porous pavements, grass swales, catchbasin cleaning, and street cleaning (in combinations and at many source areas as well as the outfall location)

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22 Summary of WinSLAMM BMPs Infiltration Facilities Wet Ponds Porous Pavement Biofiltration Street Sweeping Catch Basins Grass Swales User-Specified Land Cover Changes Land Use Changes

23 Input Parameters Rainfall Pollutant Data Land Use Data Optional BMPs Existing Proposed Output Runoff Pollutant Loading

24 Output Particulate and Pollutant Loading (lbs and mg/l) Runoff (cubic feet) Output options Again, without calibration results should be considered relative, not absolute

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26 D&R Canal NPS Study NJWSA, SWM Consulting, Princeton Hydro 58 Infalls to Canal Ranked by predicted Particulate and Phosphorous Loads Applied BMPs to Top 15 Infalls GIS Interface created Phase II Implementation of 6 BMPs

27 South Bound Brook Borough D&R Canal Franklin Township D&R Canal D&R Canal

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30 Regional Stormwater Management Plan for Deal Lake

31 For The Deal Lake RSWMP WinSLAMM was used to evaluate a myriad of stormwater management options This included structural BMPs and maintenance type activities such as street sweeping Model was used to evaluate sub-watershed specific pollutant load reductions Model used to assess existing and build out land development scenarios

32 Deal Lake Watershed Highly urbanized Much of development pre-dates need for any stormwater management Sanitary and stormwater collection system crossconnection exist Limited opportunities for the construction of regional BMPs Extensive opportunities for upgrade and retrofit of existing BMPs Potential value in disconnecting impervious and increasing street sweeping

33 Deal Lake Watershed- Existing

34 Deal Lake Watershed- 20 Yr Build Out

35 WinSLAMM Input Parameters NJDEP LU/LC Classification Rural Residential Low Density Residential Medium Density Residential High Density Residential Commercial/Services Industrial/Extractive Mining Athletic/Recreational Transportation Shrub/Brush Forest Other Urban/Recreational Orchards/Old Fields Crop/Pasture/Agriculture Lakes/Wetlands WinSLAMM Land Use Classification Residential Commercial Industrial Institutional Freeway Other Urban Not applicable

36 Pollutant Loading Results Via WinSLAMM

37 Modeling Approach Source area BMPs modeled in WinSLAMM for this analysis included disconnected commercial parking, wet ponds, street sweeping, and manufactured treatment devices. Modeling was based on 3,367 rainfall events (40- year rainfall database) BMPs were analyzed for pollutant removal total particulate solids total phosphorus not anticipated that any fecal coliform will be removed by the modeled BMPs.

38 Deal Lake Watershed-Major Outfalls

39 Results Significant pollutant reductions attributable to the retrofit installation of manufactured treatment devices Wet pond retrofits the second best level of treatment, and could be feasible at some of larger commercial sites. Could reduce particulate solids loads by approximately 41 percent and TP loads by 40 percent. Street sweeping had little impact on the reduction of either particulate solids or TP

40 Projected Particulate Solids Reductions

41 Projected Total Phosphorus Reductions

42 Summary Pollutant load modeling in general is an important tool in the formulation of stormwater management solutions With models can evaluate present and future land use scenarios and positive impacts of different BMPs WinSLAMM is particularly well suited for this type of application.

43 Summary For the NJWSA study the model helped to better identify greatest problem areas, provided BMP selection guidance and where additional sampling for calibration should be conducted For Deal it was used to develop annual pollutant load estimates for each subwatershed area and to analyze the pollutant reduction capabilities of the BMPs considered for implementation For both projects, provided an objective and directed means of planning future pollutant load reduction objectives

44 Thanks Q&A Stephen J. Souza, Ph.D. Jacob E. Helminiak, P.E. Princeton Hydro, LLC 1108 Old York Rd. Ringoes, NJ