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The Rain File (“.RAN”), which specifies rainfall events, duration, and depth for the modeled period, is regionally specific and should be developed for the study area. The [https://www.ncdc.noaa.gov/cdo-web/search National Oceanic and Atmospheric Administration] (NOAA) maintains a searchable database that can be used to search for hourly precipitation data based by city or geographic region (e.g., zip code). Local area airports (e.g., Minneapolis Saint Paul International Airport) are another resource that can be used to develop required precipitation data inputs. As described in model documentation, rainfall input “.RAN” files can be created within the Rainfall File Editor (“Utilities → Parameter Files → Rainfall Files”).
 
The Rain File (“.RAN”), which specifies rainfall events, duration, and depth for the modeled period, is regionally specific and should be developed for the study area. The [https://www.ncdc.noaa.gov/cdo-web/search National Oceanic and Atmospheric Administration] (NOAA) maintains a searchable database that can be used to search for hourly precipitation data based by city or geographic region (e.g., zip code). Local area airports (e.g., Minneapolis Saint Paul International Airport) are another resource that can be used to develop required precipitation data inputs. As described in model documentation, rainfall input “.RAN” files can be created within the Rainfall File Editor (“Utilities → Parameter Files → Rainfall Files”).
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The remaining parameter files (Runoff Coefficient File (“.RSVX”), Particulate Solids Concentration File (“.PSCX”), Source Area PSD and Peak to Average low Ratio File (“.CSV”), Particle Size Parameter Files (“.CPZ”), Street Delivery Files (“.STD”), and Pollutant Probability Distribution Files (“.PPDX”)) contain input values that must be generated from literature values, case studies, or water quality monitoring data. For this reason, default parameter files have been generated for several geographic locations across the United States and are provided in WinSLAMM documentation. Additionally, some state and local agencies have developed state-wide or regional WinSLAMM input parameter files. For this reason, it is recommended that the engineer or designer first determine if local or regional parameter files have been developed before utilizing default regional parameter files provided in the WinSLAMM model files. Figure 19 shows regional coverage of default WinSLAMM parameter files. As shown, the “Great Lakes” provides coverage of the majority of Minnesota and should be used if local or regional parameter files are not available for the study area.
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'''Special Consideration(s)''':<br>
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*The rainfall editor within WinSLAMM can be used to make Rain File(s) (“.RAN”) unique to the study area (“Utilities &rarr; Parameter Files &rarr; Rainfall Files”).
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*Parameter files can be viewed and edited from “Utilities &rarr; Parameter Files”.
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*Default parameter files unique to each “Parameter File Region” (see Figure 19) are included in WinSLAMM program files.

Revision as of 18:59, 15 August 2019

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The Source Loading and Management Model (WinSLAMM) is a proprietary stormwater quality model originally developed for the USGS for the evaluation of non-point pollution in urban areas and pollutant removal at water quality BMPs. WinSLAMM uses experimentally derived runoff coefficients to predict runoff and associated pollutant loading from a number of land use types. A unique feature in WinSLAMM is that within defined land use types (e.g., commercial, residential, etc.), the program tracks loading from many different types of source areas (e.g., roofs, parking lots, etc.) and further distinguishes source areas using source area parameters (e.g., is the roof flat or pitched? Does the roof drain to a pervious surface? etc.). WinSLAMM provides this level of specificity so that unique runoff coefficient and pollutant loading assumptions can be applied to sources areas within land use types, allowing for refinement of runoff and pollutant loading results.

WinSLAMM predicts pollutant removal at water quality BMPs based on correlation to experimental results (empirical) as well as modeling the generation and removal of particulates through sedimentation and filtration (physically based). By modeling hydraulic performance at BMPs and physically tracking the particle scale distribution (PSD) through BMPs, WinSLAMM is capable of modeling bypass from BMPs and is capable of predicting performance of BMPs in series (i.e., treatment trains). WinSLAMM is a continuous model which can produce results for long term simulations and produce results for individual rainfall events. It should be noted that WinSLAMM simulations are done in batch mode, which means that it is not modeling individual rainfall events in real-time, and accounting for antecedent moisture conditions for pervious runoff, the way that P8 does.

WinSLAMM is a versatile program suitable for TMDL applications ranging from TMDL development, to demonstrating Waste Load Allocation (WLA) and permit compliance from individual municipal separate storm systems (MS4s). Download links for WinSLAMM and related documentation are provided below. As noted above, WinSLAMM is a proprietary model which needs to be licensed or purchased before use.

Note: information provided in the following subsections does not reiterate or re-present information readily available in model documentation files. Instead, guidance provided in this document provides engineers and planners with recommendations for development of model inputs, provides guidance for interpreting and summarizing model results, provides supplementary information not included in model documentation, and provides examples showing how WinSLAMM can be used to demonstrate TMDL compliance.

Applicability to demonstrating WLA compliance

WinSLAMM is a continuous water quality model capable of summarizing runoff and associated total suspended solids (TSS) and total phosphorus (TP) generation, removal, and outflow loading from individual catchments, individual BMPs and junctions, or as a model wide summary. Additionally, because WinSLAMM models the particulate and pollutant particle-scale distribution through filtration and sedimentation BMPs and models hydraulic performance of BMPs based on watershed loading and BMP dimensions, the model is capable of accurately predicting pollutant removal through BMPs in series as well as predicting runoff and pollutant bypass from undersized undersized BMPs. Due to this flexibility, WinSLAMM is capable of providing accurate pollutant removal estimates regardless of BMP network and subwatershed configuration, and is capable of demonstrating compliance to mass-based Water Quality Based Effluent Limits (WQBELs), concentration-based WQBELS, and areal-loading based WQBELS (e.g., lbs of TSS per acre per year) for both TSS and TP.

Model inputs

The following subsections outline data sources and special consideration related to model inputs, model setup, and model initialization. Note: these subsections do not represent information readily available in Model documentation, but instead highlight data sources (e.g., spatial datasets), special consideration, and important notes for engineers and planners to consider while generating model inputs.

Current file data: parameter files

WinSLAMM requires a number of parameter files to generate runoff, particulate loading, and pollutant accumulation and washoff from source areas within each land use type. Each of the required parameters files is described briefly, below:

  • Rain File (".RAN"): specifies rainfall event date, duration, and depth for the modeled period.
  • Runoff Coefficient File (“.RSVX”): specifies the runoff coefficient (Rv) for each source area as a function of rainfall event depth.
  • Particulate Solids Concentration File (“.PSCX”): specifies the particulate solids concentration (mg/L) for each source area as a function of rainfall depth.
  • Source Area PSD and Peak to Average Flow Ratio File (“.CSV”): specifies the particle scale distribution (PSD) file (“.CPZ”) and the peak-to-average flow ratio for each source area.
    • Particle Size Parameter Files (“.CPZ”): specifies the PSD for particulates generated from a WinSLAMM source area. Unique PSD “.CPZ” files can be applied to each source area.
  • Street Delivery File (“.STD”, six (6) files): specifies the washoff coefficient for street textures as a function of rainfall depth. Note: unique street delivery files can be applied to road surface sources areas for each of the six (6) land use types.
  • Pollutant Probability Distribution Files (“.PPDX”): specifies the particulate pollutant concentration associated with generated particulate (mg/kg) and the dissolved pollutant concentration (mg/L) for all modeled pollutant constituents from all source areas within each land use type.

The Rain File (“.RAN”), which specifies rainfall events, duration, and depth for the modeled period, is regionally specific and should be developed for the study area. The National Oceanic and Atmospheric Administration (NOAA) maintains a searchable database that can be used to search for hourly precipitation data based by city or geographic region (e.g., zip code). Local area airports (e.g., Minneapolis Saint Paul International Airport) are another resource that can be used to develop required precipitation data inputs. As described in model documentation, rainfall input “.RAN” files can be created within the Rainfall File Editor (“Utilities → Parameter Files → Rainfall Files”).

The remaining parameter files (Runoff Coefficient File (“.RSVX”), Particulate Solids Concentration File (“.PSCX”), Source Area PSD and Peak to Average low Ratio File (“.CSV”), Particle Size Parameter Files (“.CPZ”), Street Delivery Files (“.STD”), and Pollutant Probability Distribution Files (“.PPDX”)) contain input values that must be generated from literature values, case studies, or water quality monitoring data. For this reason, default parameter files have been generated for several geographic locations across the United States and are provided in WinSLAMM documentation. Additionally, some state and local agencies have developed state-wide or regional WinSLAMM input parameter files. For this reason, it is recommended that the engineer or designer first determine if local or regional parameter files have been developed before utilizing default regional parameter files provided in the WinSLAMM model files. Figure 19 shows regional coverage of default WinSLAMM parameter files. As shown, the “Great Lakes” provides coverage of the majority of Minnesota and should be used if local or regional parameter files are not available for the study area.

Special Consideration(s):

  • The rainfall editor within WinSLAMM can be used to make Rain File(s) (“.RAN”) unique to the study area (“Utilities → Parameter Files → Rainfall Files”).
  • Parameter files can be viewed and edited from “Utilities → Parameter Files”.
  • Default parameter files unique to each “Parameter File Region” (see Figure 19) are included in WinSLAMM program files.