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PostFire Peak Flow and Erosion Estimation >
USGS Regression Methods
USGS Regression methods
The USGS Regression method
is the most commonly used postfire 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
floodfrequency 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 floodfrequency relations are often called, and expressed as a form of, "USGS regression equations,"
since a regression analysis was used to develop the floodfrequency 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
 Find the USGS Regression equations for the area of interests.
 Collect the basin characteristics of burned areas.
 Collect information about the burned area,
such as percentage of high and moderate sil burn severity areas.
 Determine design/damaging storm, including
storm intensity, duration, and recurrence interval.
 Estimate prefire runoff assuming no fires and unburned area for the area of interest.
 Determine the
percent runoff increase for high and moderate soil burn severity area.
 Determine modifier that is defined as a ratio of
postfire to prefire runnoff.
 Estimate postfire runoff by multiplying the modifier and prefire
runoff (or use alternatives).
Advantages
The following were advantages to applying the USGS Regression method fo postfire runoff and erosion estimation.
The USGS Regression Method:
 is applicable for estimating both pre and postfire peak flow;
 estimates peak flow, regardless of the storm duration and intensity;
 is appropriate for larger watersheds (>5 mi^{2});
 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 postfire runoff and erosion estimation.
 It does not estimate erosion.
 It does not consider postfire debris flow/torrent.
 The user must find the adequate USGS Regression equations for the
watershed in the prefire condition.
 The user must find the adequate USGS Regression equations for the
watershed in the postfire condition (if any).
 The user must determine the modifier, or the soil water
repellancy and postfire 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 postfire road treatments for BAER teams:
methods, treatment effectiveness, and decisionmaking tools for rehabilitation.
Gen. Tech. Rep. RMRSGTR. Fort Collins, CO: U.S. Department of Agriculture,
Forest Service, Rocky Mountain Research Station (in preparation).
