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System for Urban Stormwater Treatment and Analysis IntegratioN Model


SUSTAIN is a decision support system was developed to:

  • assist stormwater management professionals in developing implementation plans for flow and pollution control to protect source waters and meet water quality goals.
  • assist watershed and stormwater practitioners to develop, evaluate, and select optimal BMP combinations at various watershed scales on the basis of cost and effectiveness.

SUSTAIN is a tool for answering the following questions:

  • How effective are BMPs in reducing runoff and pollutant loadings?
  • What are the most cost-effective solutions for meeting water quality and quantity objectives?
  • Where, what type of, and how big should BMPs be?

SUSTAIN was developed by Tetra Tech, an environmental engineering and consulting service.

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SUSTAIN has seven modules:

  1. Framework Manager
  2. BMP Siting Tool
  3. Land Module
  4. BMP Module
  5. Conveyance Module
  6. Optimization Module
  7. Post-Processor

The modules are integrated under a common ArcGIS platform, which performs hydrologic and water quality modeling in watersheds and urban streams. It searches for optimal management solutions at multiple-scale watersheds to achieve desired water quality objectives based on cost effectiveness.

  1. Framework Manager - Serves as the command center of SUSTAIN. It manages the data exchanges between system components and coordinates external inputs, calls various modeling components (i.e., Land, BMP, conveyance), and provides output information to the post-processor.

  2. BMP Siting Tool - Supports users in selecting suitable locations for common structural BMPs that meet the defined site suitability criteria such as drainage area, slope, hydrological soil group, groundwater table depth, road buffer, stream buffer, and building buffer.

    BMPs are classified and conceptualized in SUSTAIN as scale-based and type-based. The scale-based category classifies BMPs according to the size of the application area, such as lot-, community-, and watershed-scales. The type-base category classifies BMPs into three types according to the geometric properties:

    • Point BMPs: practices that capture upstream drainage at a specific location and may use a combination of detention, infiltration, evaporation, settling, and transformation to manage flow and remove pollutants.
    • Linear BMPs: narrow linear shapes adjacent to stream channels that provide filtration of runoff, nutrient uptake, and ancillary benefits of stream shading, wildlife habitat, and aesthetic value.
    • Area BMPs: land-based management practices that affect impervious area, land cover, and pollutant inputs.

    The following structural BMP options are currently supported:

    BMP Option BMP Type
    Bioretention Point LID
    Cistern Point LID
    Constructed Wetland Point BMP
    Dry Pond Pont BMP
    Grassed Swale Linear BMP
    Green Roof Area BMP
    Infiltration Basin Point BMP
    Infiltration Trench Linear BMP
    Porous Pavement Area BMP
    Rain Barrel Point LID
    Sand Filter (non-surface) Linear BMP
    Sand Filter (surface) Point BMP
    Vegetated Filter strip Linear BMP
    Wet Pond Point BMP
  3. Land Simulation Module - Computes runoff and pollutant loads from land in one of two ways:

    1. by default, the land module computes the hydrograph and pollutograph using algorithms adapted from SWMM5 (Storm Water Management Model), and
    2. sediment algorithms adapted from HSPF (Hydrological Simulation Program - FORTRAN).

    The module also supports the import of externally generated time series data.

  4. BMP Simulation Module - Provides process-based simulation of flow and pollutant transport for a wide rage of structural BMPs. It is designed so that new BMPs and alternative simulation techniques can be added. The table below is a summary of major processes currently included in the module. Option 1 is the default option; however, users can select the preferred simulation method from either option depending on the available data and required level of detail.

    Process Option 1 Option 2
    Flow routing Stage-outflow using weir and/or orifice equations For swale: kinematics routing by solving the coupled continuity equation and Manning's equation.
    infiltration Green-Ampt method Holtan-Lope equation
    Evapotranspiration Constant evapotranspiration (ET) rate or monthly average value or daily values Potential ET using Harmon's method
    Pollutant routing Completely mixed Continuously stirred tank reactor (CSTRs) in series
    Pollutant removal 1st order decay Kadlec and Knight's (1996) 1st order kinetic method
    Buffer strip (sheet flow) flow routing Kinematics waver overland flow routing  
    Buffer strip sediment trapping University of Kentucky sediment interception simulation method as applied in VFSMOD  
    Buffer strip (sheet flow) pollutant removal 1st order decay  

    The BMP module includes two additional functionalists:

    • BMP Cost Estimation - The cost database in SUSTAIN is expressed in terms of unit costs of individual construction components of a BMP. The unit costs were compiled from wholesale and retail companies that provide raw materials for BMPs, and from multiple sources of BMP implementation at the county, state, and federal levels. The use of this unit cost approach, rather than the entire bulk BMP installation, aims to minimize differences encountered from site or locality factors. Users have the option to override the built-in data with the locally derived information.
    • Aggregation of Distributed BMPs - The aggregate BMP approach allows users to assess the effectiveness of multiple BMPs. It is used to represent the aggregate characteristics of distributed BMPs while reducing the user's effort to model set-up and computation time needed for simulation and optimization. Aggregate BMPs evaluate storage and infiltration characteristics of multiple BMPs simultaneously without explicit recognition of their spatial distribution and flow and pollutant routings.

  5. Conveyance Simulation Module - Performs routing of flow and pollutants through a conduit. In SUSTAIN, conduits are pipes or channels that move water from one node to another in a watershed routing network. The cross-sectional shapes of a conduit can be selected from a variety of standard open and closed geometries. Irregular natural cross-section shapes are supported, as are user-defined closed shapes. Flow and pollutant routing are simulated using transport algorithms in SWMM5, and sediment routing using sediment transport algorithms in HSPF.

  6. BMP Optimization Module - Identifies cost-effective BMP placement and selection strategies based on a pre-determined list of feasible sites and applicable BMP types and size ranges. This module uses evolutionary optimization techniques to search for cost-effective BMPs that meet user-defined decision criteria. Currently, two search algorithms are implemented in SUSTAIN: scatter search and non dominated sorting genetic algorithm-II (NSGA-II).

    Operationally, the optimization module incorporates a tiered approach that allows for cost effectiveness evaluation of both individual and/or multiple nested watersheds to address the needs of both regional- and local-scale applications. Tier-1 performs the optimization search to develop cost effectiveness curves for each tier-1 sub watershed. Tier-2 uses the tier-1 solutions to construct a new optimization search domain and run the transport module, if needed, to develop the combined cost-effectiveness curve for the entire tier-2 watershed.

  7. Post-Processor - Using Microsoft Excel, the post processor provides a centralized location in SUSTAIN for analyzing and interpreting simulation outputs at multiple locations, and for scenarios (e.g., existing development with and without BMPs, and pre-development conditions) and parameters of interest (e.g., inflows, outflows, pollutant loads and concentrations). The simulation outputs contain hourly or sub-hourly data, and can span several years depending on the length of simulation. The post processor allows users to evaluate simulation results that are highly variable in magnitude, duration, intensity, treatment containment volume, attenuation, and pollutant removal effectiveness. This is achieved by using specific graphical and tabular reports, including storm event classification, storm event viewer, storm performance summary, and cost-effectiveness curves.

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Watershed Planning Process Uses of SUSTAIN
Identify Problem(s) & Set Goals
Generalized assessment of management impacts and load reduction potential
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Develop Plan
Predict load reduction and cost for multiple management alternatives
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Implement Plan
Support selection of an optimal implementation plan

Evaluate project phases (cost and load reduction at each phase)
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Track Progress
Recalibrate SUSTAIN based on newly collected data

Evaluate future benefits of implementation and/or adaptation of plan
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Achieve Management Goals

Various practitioners, municipalities, and watershed groups at the regional and local level can use the SUSTAIN framework to address a variety of planning:

  • Developing TMDL implementation plans
  • Identifying management practices to achieve pollutant reductions under a municipal separate storm sewer system (MS4) stormwater permit
  • Determining optimal green infrastructure strategies for reducing volume and peak flows to combined sewer systems
  • Evaluating the benefits of distributed green infrastructure implementation on water quantity and quality in urban streams
  • Developing a phased BMP installation plan using the cost effectiveness curve

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EPA will provide technical support to users through a contractor for a period of time governed by the availability of funds.


01/2013 SUSTAIN Version 1.2 (EXE) (19.9 MB)
06/26/2012 SUSTAIN Version 1.2 Installation Guide (PDF) (5 pp, 296 KB)
Self-extracting installation program for SUSTAIN 1.0 (EXE) (16.7 MB)
After running this self-extracting installation program, please find a step-by-step guide under a folder "..\SUSTAIN\Documents" (usually C:\Program Files\SUSTAIN\Documents). Please also try general exercises of SUSTAIN presented at the same folder.
04/02/2012 SUSTAIN Engine Version 1.0 (ZIP) (585 KB): Modeling engine source codes
04/02/2012 SUSTAIN Interface Version 1.0 (ZIP) (6.19 MB): Program interface source codes
04/02/2012 SUSTAIN Siting Tool Version 1.0 (ZIP) (1 MB): BMP siting tool source codes
Report on Enhanced Framework (SUSTAIN) and Field Applications for Placement of BMPs in Urban Watersheds (150 pp, 5.67 MB) (EPA/600/R-11/144) November 2011 | Abstract
SUSTAIN--A Framework for Placement of Best Management Practices in Urban Watersheds to Protect Water Quality (EPA/600/R-09/095) September 2009 | Abstract
06/24/2007 SUSTAIN - An EPA BMP Process and Placement Tool for Urban Watersheds (PDF) (23 pp, 1 Mb) Reprinted with Permission for Proceedings of the TMDL 2007 Specialty Conference, June 24-27, 2007, Bellevue, Washington.  Copyright 2007 Water Environment Federation: Alexandria, Virginia.
03/11/2010 Introductory Web cast on SUSTAIN - Slides. (PDF) (98 pp, 6 Mb)
  Poster: SUSTAIN - A BMP Process and Placement Tool for Urban Watersheds. (PDF) (1 pg, 1.2 Mb)
03/2013 "Stormwater Management for TMDLs in an Arid Climate: A Case Study Application of SUSTAIN in Albuquerque, New Mexico" (PDF) 101(pp, 9 MB) Publication No. EPA/600/R-13/004.
The SUSTAIN installation requires ESRI's ArcGIS 9.3 and the Spatial Analyst extension. The system also requires Microsoft Excel 2003 which is used as a post-processor for analyzing and interpreting results.
You will need Adobe Acrobat Reader to view Adobe PDF documents. Read more About Portable Document Format File.

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Ariamalar Selvakumar, EPA
For information on release and related research
Technical support team
For issues related to installation and use

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