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TR-55
Seven of BAER team members (7%) used TR-55 to calculate post-fire runoff increase (Foltz and others 2008). The TR-55 requires the runoff curve number (CN) as an input parameter; therefore, it can be considered as a Curve Number method. The TR-55 was released as a simplified procedure to calculate the storm runoff volume, peak flow rate, hydrograph, and storage volume for storm water management structures in small watersheds in urban areas, assuming the NRCS Type II rainfall distribution for all calculations (USDA SCS 1975). Later, a major revision was made to improve the model by adding three more rainfall distributions (Type I, IA, and III), programming the computations, and estimating the time of concentration using split separate flow phases (USDA SCS 1986).
To use TR-55, you will need WinTR-55 .
Input Requirement
Required input data is as follows (USDA NRCS 2005b):
- identification data;
- dimensionless unit hydrograph;
- storm data;
- rainfall distribution;
- area (acre);
- Runoff Curve Number (CN); and
- time of concentration (Tc) details.
Steps
- Run TR-55 for pre-fire watershed conditions.
- Determine the CNs for burned areas within the watershed.
- Run TR-55 for post-fire watershed conditions.
Advantages
The following were advantages to applying the WinTR-55 for post-fire runoff and erosion estimation. WinTR-55:
- is applicable for estimating peak flow;
- estimates time to peak;
- is applicable to larger watersheds(< 25 mi2); and
- uses both English and metric units.
Disadvantages
The follwing were disadvantages to applying the WinTR-55 for post-fire runoff and erosion estimation. WinTR-55:
- does not estimate erosion;
- does not consider post-fire debris flow/torrent;
- only considers 24-hour storm duration, so it is not applicable to the regions where the damaging storm duration is much shorter, such as 15 or 30 minutes;
- requires the user to determine pre-fire and post-fire CNs, which are sensitive parameters, so the estimated peak flow is subjective to users; and
- does not provide guidelines to determine post-fire CN, except in Regions 1 and 3.
Example Results
The 2002 Bullock Fire in the Coronado National Forest, Arizona
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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