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Environmental Modeling Community of Practice

Gray Tool


The Gray tool represents sewer networks and storage-based stormwater control structures. It was developed for the Hydrological Simulation Program-- FORTRAN (HSPF) model users. It uses HSPF’s RCHRES module to model how certain structural best management practices (BMPs) such as detention basins (wet ponds, treatment wetlands, etc.) mitigate the impacts of stormwater runoff and associated water quality constituents. The tool is accessible at . In its current version, the tool represents open channels and flow control devices (weirs and orifices). The open channel component has five shape choices, and each shape is represented by a depth-area-volume-flow relationship known as hydraulic function table or FTABLE. The available open channel’s shapes are circular, parabolic, rectangular, triangular, trapezoidal, and natural. Outflow control structures consist of V-notch, sharp-crested, rectangular, and broad-crested weirs, and under-drain and riser pipe orifices. For each channel shape, users can select an open channel with or without a flow control device. In many applications, users select only an open channel, while in other applications they may select an open channel with one or more flow control devices. Note that HSPF allows a maximum of five flow exits in one FTABLE. The gray tool enables HSPF users to extend the model’s application to urban watersheds with sewer system networks.

How to Run Gray Tool

Run the Gray Tool in your web browser.

Detailed information on how to run the program are given in the tutorials 10TechNote 09 Web Based HSPF Toolkit to Support Low Impact Development LID and Other Urban Stormwater Modeling Applications (PDF)

Java Download

If you cannot see the applet when you open the web page in the browser, go to and download the latest Java Runtime Engine (JRE), which is under the Java SE category on the Oracle website. We recommend reading the tutorial before attempting to use the tool.

Contact the Author

For questions and suggestions, please contact CEAM Help Desk .

Citation of Gray Tool

For citation, please use: Center for Exposure Assessment Models (2012). HSPF BMP Toolkit. National Exposure Research Laboratory. Athens, Georgia.