Since 2001, USEPAs Office of Research and Development (ORD)  has been developing a new simulation model/decision-making tool designed to answer some critical stormwater management questions, including how to determine selection and placement of BMPs at strategic locations, including:

How effective are BMPs in reducing runoff and pollutant loadings?

Where, what type, and how big should BMPs be?

What are the most cost effective BMPs for meeting water quality and quantity objectives?

The tool, SUSTAIN (System for Urban Stormwater Treatment and Analysis Integration Model) is designed for use by watershed and stormwater practitioners to develop, evaluate, and select optimal BMP options for various watershed scales with a major focus on cost and effectiveness.

SUSTAIN is designed to integrate GIS analysis and visualization, watershed/BMP simulation, cost, and system optimization.  It incorporates an innovative concept of developing a cost-effectiveness curve for watershed decision making.  In addition, an equally innovative multi-tier concept was incorporated for performing staged optimizations from smaller watersheds to a larger watershed.

The SUSTAIN Version 1.0 was released in October 2009.  Prior to this release, four workshops were held in selected EPA Regions, and additional workshops are being planned.  ORD has committed additional resources to showcase applications and perform needed enhancements to better facilitate the setup and application of SUSTAIN while improving output accuracy and credibility.

The software and technical report are available for download here.

SUSTAIN includes four key components:

(1)  a BMP site evaluation tool which uses the ArcGIS platform and user-guided rules to determine site suitability for various BMP options,

(2)  a watershed module that integrates locally derived data with watershed simulation models to predict flow and pollutant loading,

(3)  a stand-alone BMP module that performs process-based simulation, and

(4)  an optimization module that performs cost estimating and combines performance and cost data of various design alternatives.

SUSTAIN is designed to link with external models for inputs of flow and pollutant time series.  It also has internal stand-alone sub-modules for performing watershed/landscape runoff simulation, BMP process simulation, conduit routing, and stream conveyance and pollutant routing.  The framework includes a suite of system and interface capabilities.  System features emphasize the use of GIS-based visualization and support for developing watershed simulation networks that may include sequences of land parcels, management practices, and stream reaches.

Various practitioners, municipalities, and watershed groups at the regional and local levels can use SUSTAIN to address a variety of stormwater management planning questions on:

(1)  developing TMDL implementation plans,

(2)  identifying management practices to achieve pollutant reductions in an area under an MS4 stormwater permit,

(3)  determining upstream source control strategies for reducing volume and peak flows to CSO systems, and

(4)  evaluating the benefits of distributed BMP implementation on water quantity and quality in urban streams.

That’s the background and set-up.  We hope you go to the website and attempt to familiarize yourself with this remarkable new tool.

First Reaction/Review

EPA hosted a free 2-hour webcast on March 11, 2010 that provided an overview of SUSTAIN, descriptions of the major system modules, and an example application in using the SUSTAIN framework.  Speakers included Dennis Lai (USEPA), Leslie Shoemaker, and John Riverson (both from Tetra Tech, EPAs consultant on the project).  The webcast targeted watershed management professionals wanting to learn how to use and apply SUSTAIN framework for evaluation and decision-making of stormwater management options.

We participated in the webcast and have a variety of comments and questions:

PROS

1.  In so many ways, EPAs SUSTAIN (and the bright minds at Tetra Tech) constitutes a giant leap forward in the science and art of stormwater management.  Not long ago, stormwater management in most Pennsylvania municipalities either was nonexistent or consisted of figuring out how many detention basins to excavate.  SUSTAIN is a vivid demonstration of how far we have advanced.  SUSTAIN and its amazing family of linked models is awesome in its complexity and sophistication, essential if it is to accomplish its ambitious mission.

2.  Although stormwater management guidance, including PADEPs guidance in the December 2006 BMP Manual has grown much more comprehensive and complete, there remains much ”irrationality” in the selection of BMPs across Pennsylvania development projects.  Although we continue to argue that stormwater management planning/engineering/design involves both science and art, some sort of mechanism like SUSTAIN would be enormously helpful, especially in certain less “experienced” portions of Pennsylvania.  SUSTAIN could help us do better.

CONS

1.  The challenge in such complex modeling efforts is to somehow capture the full complexity of the nation’s natural systems, watersheds, and subtleties of every site, together with the full variability of so many different development programs.  This seems like an overwhelming task! As we speak, we confess that we have not been able to download and study every modeling element of SUSTAIN and assess the myriad assumptions which are being made, including assumptions which may not be valid in the modeling, depending upon natural system and watershed and site, as well as assumptions which simply may not be included in the modeling, but which might be important when designing and engineering a stormwater management plan for Development Proposal A at Site X.

2.  In one sense, our comment above is premature.  EPA and Tetra Tech have been developing this modeling tool for nearly 10 years with enormous effort.  The problem for us users is that it takes vast numbers of hours to assess the remarkable modeling package, including the vast number of assumptions which have gone into model development.  The 2-hour webcast was extremely compressed, even rushed in our minds.  We simply did not have time to digest everything that Tetra Tech was saying. Our sense is that even developing a basic understanding of SUSTAIN requires a full day of explanation and presentation.

3.  For example, if we understood Tetra Tech correctly in the webcast, it would seem that the water quality modeling in SUSTAIN very much “hangs” on work of the soil.  Although we are great believers in use of soil mechanisms for water quality renovation, the bulk of these mechanisms function for particulate-form pollutants, such as sediment and phosphorus.  For solubilized pollutants such as nitrogen forms, some organics, and others, soil-based mechanisms are not especially effective. Especially in the wonderfully expanding world of vegetative-based “green” BMPs, this aspect of water quality needs to be addressed and taken into account in this modeling (nitrogen is an important issue in so many Chesapeake Bay tributary municipalities).

Again, assuming we are understanding SUSTAIN correctly, it is incredibly important that all aspects of the modeling including all assumptions used in the modeling be comprehensive and complete. Like a chain, quality of modeling output cannot be expected to be any more accurate than the quality of its weakest link - than any of its many constituent assumptions.

4.  We need evidence of calibration and verification of this modeling.  We want to see how SUSTAIN applications would have treated existing sites which we feel have successful stormwater management plans.

5.  Lastly, and this comment is echoed above, users of SUSTAIN - whomever that might be in Pennsylvania - will have to invest substantial resources in this modeling tool for any kind of application for all the reasons discussed above. These days, who has these resources?  Certainly it’s hard to imagine individual MS4 municipalities being able to apply SUSTAIN in any context, although watershed groupings of municipalities might be able to consider SUSTAIN applications.  (In upcoming blogs, StormwaterPA hopes to report on both some interesting work being conducted by Pennsylvania Environmental Council in the Wissahickon as well as Chester County’s Brandywine Valley Association with the Chester County Water Resources Authority for the Brandywine Creek…)

Did anyone else attend the webinar?

Download the software and tinker?

Comments?

National, Stormwater BMPs BMPs, CSO, green infrastructure, MS4, PA BMP Manual, PA DEP, peak rate, TMDL, volume control, water quality