Getting More Bang for Your Buck: How to Select a TMDL Compliance Tool

By Deb Sahoo, Hal Clarkson, Ben Hammond, Gil Inouye, Crystall Muller and Nadja Turek

“There’s an app for that.”

Apple made the phrase famous, but its concept rings true. Whether you are looking to order take-out, manage your finances or simplify a task, a plethora of web-based tools exist to meet your needs. But how do you know which one to select?

Technology has advanced the engineering industry by what seems like light years. So many components of design, measurement and maintenance have been computerized and networked. Take, for example, the world of municipal water management—more specifically, stormwater management.

When one of our stormwater clients recently came to us requesting a web-based tool for creating impactful reporting visuals to support total maximum daily load (TMDL) compliance efforts, educate the public and demonstrate improvements to city council, we expected to find a large number of potentially useful applications. Before jumping into the development of a new, fully-customized tool, we evaluated those already in use within the industry.

For this particular request, we searched for a GIS-based tool that could be used with simple inputs to plan best management practice (BMP) installations and demonstrate their potential impacts. At a minimum, the application required the ability to perform the following functionalities:

  • Select specific watershed areas and land uses
  • Predict pollutant loadings
  • Add structural and non-structural BMPs and BMP costs
  • Display and manipulate existing monitoring data
  • Calculate loadings with BMP interventions
  • Tabulate costs per pound of removed pollutants
  • Create visuals for demonstrating compliance and needs
  • Estimate implementation costs
  • We also were looking for a customizable application robust—yet flexible—enough to support future upgrades.

We evaluated the following eight applications, and here’s what we found.


The United States Geological Survey (USGS) StreamStats tool can be used to delineate watersheds and obtain very specific watershed characteristics. StreamStats computes the flow statistics of ungauged watersheds using regression equations developed from gauged watersheds. This web-based tool does not require a desktop installation. While StreamStats does not currently support water quality modeling, portions of this tool could be used to develop the desired TMDL tool.

WIP Tools

Deployed as an extension in ArcMap, the Brown and Caldwell Watershed Improvement Plan (WIP) Tools is a grid-based GIS model developed to evaluate hydrologic and water quality conditions and assist in watershed improvement planning. Using various hydrologic and water quality principles, WIP Tools creates a variety of grids representing the watershed responses based on analyzed physical parameters. These grids are overlaid on a digital elevation model to identify high pollutant loads; the potential impacts of proposed projects on these loads are also evaluated. A proprietary tool, WIP requires user expertise to simulate different watershed conditions.

Automated Water Quality Project Prioritization Tool to Address TMDLs

Orange County, Fla., relies on a GIS-based program developed by Woolpert to address TMDLs. Drawing on several GIS layers, such as point projects, line projects, soils, land use, streets and major basins, the program uses coefficients for BMP pollutant reduction, runoff reduction and general pollutant reduction to estimate overall load reductions. All values for this data-intensive model are primarily based on the Schuler method.

Infraworks 360

Infraworks 360 is a non-GIS Autodesk extension that uses hydrologic models such as TR 55 and the 95th percentile rainfall event to calculate volumes. This volume-control green infrastructure tool employs 3D renderings and visualizations of the BMPs within the Infraworks 360 framework. This proprietary program lacks water quality simulation capabilities and requires user expertise to perform simulations and rendering.

National Stormwater Calculator 

The EPA’s National Stormwater Calculator is a publicly available desktop application used to estimate the annual rainfall amount and frequency of runoff for any location in the United States (though water quality calculations are not currently available). With access to several national databases, the calculator bases estimates on soil conditions, topography, land cover, rainfall and evaporation information. Users can select one of seven low-impact development (LID) controls to estimate runoff reductions.

Virginia Runoff Reduction Method

The Virginia Runoff Reduction Method is a free, spreadsheet-based program developed to better promote stormwater design and provide an incentive for the use of LID and environmental site design strategies. The spreadsheet, while neither user-friendly nor visually appealing, adjusts the curve number in the post-construction scenario to match the curve number in the pre-construction scenario. User-specified trapping efficiencies of the LID BMPs are then used to quantify the effectiveness of those BMPs.


Integrated Design, Evaluation and Analysis of Loading (IDEAL) is a post-construction water quality model for designing stormwater BMPs and analyzing their effectiveness in removing common stormwater pollutants such as sedimentbacterianitrogen and phosphorus. The model’s runoff treatment algorithms are process-based; runoff rates and pollutant loads can be predicted and routed through BMPs using validated technologies. Developed by Woolpert, the program is currently only available for the southeastern United States.


System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN) is a program developed by the United States Environmental Protection Agency (EPA) to help stormwater management professionals create and implement structural watershed controls that protect source waters and meet water quality objectives. This GIS-based program demands extensive watershed information, requires significant experience to perform simulations and is no longer supported by the EPA.


Our investigation revealed that in the case of TMDL compliance tools, there might not yet be an app for that.

While some of the applications did possess beneficial components, none had the visualization or communication features needed to meet our client’s requirements. We determined that rather than borrowing pieces from a variety of other programs, it might just be simpler—and more effective—to create an entirely new program specifically tailored to our client’s needs.

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