Burned Area Emergency Response Tools

Details of USGS Regression Methods

The Department of Interior U.S. Geological Survey (USGS) has developed a method to estimate magnitude and frequency of floods of both gaged and ungaged streams. The flood-frequency relations at gaged and ungaged sites were developed for various hydologic regions based on their stream gage records, basin characteristics, and numerous studies throughout the United States. These flood-frequency relations are often called, and expressed as a form of, "USGS regression equations," since a regression analysis was used to develop the flood-frequency relations.

USGS Publications

USGS regression equation methods have been incorporated into StreamStats (USGS 2007), which is a web-based tool used to obtain streamflow information. StreamStats are available for many states and are being implemented for the others. The following publications contain regression equations and post-fire peak flow information for the western United States.

Basin Characteristics

Basin characteristics include the drainage area, elevation, precipitation, free water-surface evaporation, latitude, longitude, forest and herbaceous cover, high elevation area, channel slope, soil storage capacity and permeability, and minimum and maximum January temperatures (the actual required basin characteristics may vary depending on the hydrologic regions. Fortunately, not all of these characteristics are required for a single region.)

Burned Area Information

This includes percentage of high and moderate soil burn severity areas.

Design/Damaging Storm Information

This includes storm intensity, duration, and recurrence interval.

Percent Runoff Increase

Since there are very limited studies and guidelines to determine the modifer or the percent runoff increase for high and moderate burn severity, BAER team members oftenrely on simple rules of their own. For example, some Region 1 BAER specialists used 100% runoff increase (double the runoff amount) for high/moderate soil burn severity areas in the first year of the fire, such as on the 2006 Derby Fire (Story and others 2006). Also, they assumed that 1/3 of the high soil burn severity areas had soil water repellency and a a 10-fold increase in surface runoff for the same year, and 1/6 of the areas for one year after the 2000 Skalkaho/Valley Complex Fires in Montana (unpublished data, Story 2002).

Modifier

Modifier is defined as a ratio of post-fire to pre-fire runoff and is calculated as follows:

Alternatives to Estimate Post-Fire Peak Flow

Some BAER team members in Region 1 skipped steps 6 through 8 and used a USGS Water-Resources Investigations Report (Parrett and others 2004) to estimate post-fire peak flow for their burned areas. This report provided post-fire runoff responses 1 year after a fire in three burned areas in Montana (Canyon Ferry, Ashland, and Bitterroot Fires). Once the BAER team members chose a design storm and a station with a drainage area similar in size to their burned area, they could determine the matching post-fire peak flow for their burned areas. However, the report by Parrett and others (2004) did not provide information about the size of burned areas and burn intensities within watersheds. Care should be taken when using a USGS report to estimate post-fire peak flow for burned areas when more detailed burned area conditions are available.

REFERENCES

Parrett, Charles; Cannon, Susan H.; Pierce, Kenneth L. 2004. Wildfire-related floods and debris flows in Montana in 2000 and 2001. Water-Resources Investigations Report 03-4319. Denver, CO: U.S. Geological Survey. 22 p.

Story, Mark; Johnson, Steve; Stuart, Bo; Hickenbottom, Jennifer; Thatcher, Ron; Swartz, Scott. 2006. BAER specialist report, hydrology and roads, Derby Fire. 17 p.

 

USDA Forest Service - RMRS - Moscow Forestry Sciences Laboratory
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