Stormwater guidance for Biological Assessments

In 2009, the Federal Highway Administration (FHWA), National Marine Fisheries Service (NMFS), U.S. Fish and Wildlife Service (USFWS), and the Washington State Department of Transportation (WSDOT) signed a Memorandum of Agreement (MOA) to use a common method for analyzing the effects of stormwater on Endangered Species Act (ESA)-listed fish species in Washington state. One element of the MOA is the use of the Western Washington Highway Runoff Dilution and Loading Stormwater Model (HI-RUN Model) in consultations on western Washington projects with potential stormwater effects on listed species.

Use the information below with Chapter 17: Stormwater Impact Assessment of the Biological Assessment (BA) preparation manual. In addition, find information on programmatic stormwater monitoring and the indirect effects stormwater runoff analytical method.

Eastern Washington stormwater assessment

Use the information below when assessing stormwater effects in eastern Washington. This process doesn’t involve the use of the HI-RUN model.

Western Washington stormwater assessment

The HI-RUN Model should only be used for stormwater analysis associated with BAs for western Washington and should not be used as a design tool. 

Use the Endangered Species Act Stormwater Design Checklist for Western Washington (doc 162 kb) January 2010 checklist to document pertinent information required for the HI-RUN Model, for help in developing BAs, and promoting consistency in BA content.

Two versions of the HI-RUN Model are available.

Download the HI-RUN Model to your computer prior to use. Consult the Frequently Asked Questions/Troubleshooting Guide below or contact Mark Bakeman, at, if you encounter problems or errors when using the model.

Use the information below to run the HI-RUN Model.

Programmatic stormwater monitoring

A programmatic stormwater monitoring approach was developed that provides additional data for improving the HI-RUN model’s predictions for treated and untreated runoff. This approach uses, when possible, the WSDOT National Pollutant Discharge Elimination System (NPDES) permit monitoring requirements rather than monitoring individual projects. The compiled data will improve the accuracy and reliability of the current stormwater models. Local agency projects funded by the FHWA that are similar in scope to WSDOT projects, and meet or exceed the requirements of the Highway Runoff Manual for stormwater treatment, may also be able to use this approach. 

Indirect effects stormwater runoff analytical method

Follow the Indirect Effects Stormwater Runoff Analytical Method (pdf 59 kb) to evaluate water quality impacts associated with stormwater runoff from development identified as an indirect effect of transportation projects. In an MOA signed on April 14, 2011, FHWA, NOAA Fisheries, USFWS, and WSDOT agreed to this method.