Burned Area Emergency Response Tools

USGS Regression methods

The USGS Regression method is the most commonly used post-fire runoff estimation method by BAER team members (43%) (Foltz and others 2008). 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.

To use the USGS regression methods, you will need StreamStats or USGS publications.

Input Requirement

To use the USGS Regression method, the following information is required:

• USGS Regression equations for the area of interests (burned sites);
• gaged data from the watershed of interests (if any);
• basin characteristics;
• design storm intensity, duration, and recurrence interval;
• size of high soil burn severity areas; and
• water repellency and surface runoff increase of high/moderate soil burn severity area.

Steps

1. Find the USGS Regression equations for the area of interests.
2. Collect the basin characteristics of burned areas.
3. Collect information about the burned area, such as percentage of high and moderate sil burn severity areas.
4. Determine design/damaging storm, including storm intensity, duration, and recurrence interval.
5. Estimate pre-fire runoff assuming no fires and unburned area for the area of interest.
6. Determine the percent runoff increase for high and moderate soil burn severity area.
7. Determine modifier that is defined as a ratio of post-fire to pre-fire runnoff.
8. Estimate post-fire runoff by multiplying the modifier and pre-fire runoff (or use alternatives).

    

Advantages

The following were advantages to applying the USGS Regression method fo post-fire runoff and erosion estimation. The USGS Regression Method:

• is applicable for estimating both pre- and post-fire peak flow;
• estimates peak flow, regardless of the storm duration and intensity;
• is appropriate for larger watersheds (>5 mi²);
• does not usually require detailed watershed information, such as soil and topography;
• is more accurate if gaged data is used from the watershed of interest; and
• is applicable to longer duration events, and snowmelt runoff events.

Disadvantages

the following were disadvantages to applying the USGS Regression method for post-fire runoff and erosion estimation.

• It does not estimate erosion.
• It does not consider post-fire debris flow/torrent.
• The user must find the adequate USGS Regression equations for the watershed in the pre-fire condition.
• The user must find the adequate USGS Regression equations for the watershed in the post-fire condition (if any).
• The user must determine the modifier, or the soil water repellancy and post-fire runoff increase, for high and moderate burn severity areas.
• It uses only English units.

Example Results

The 2000 Skalkaho/Valley Complex Fires in the Bitterroot National Forest, Montana

REFERENCES

Foltz, Randy B.; Robichaud, Peter R.; Rhee, Hakjun. 2008. A synthesis of post-fire road treatments for BAER teams: methods, treatment effectiveness, and decision-making tools for rehabilitation. Gen. Tech. Rep. RMRS-GTR. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station (in preparation).

USDA Forest Service - RMRS - Moscow Forestry Sciences Laboratory
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