Burned Area Emergency Response Tools

Details of TR-55

The TR-55 was released as a simplified procedure to calculate the storm runoff volume, peakflow 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). The current version of the TR-55 computer model is WinTR-55, which was revised and completely rewritten. It uses the TR-20 model (USDA NRCS 2005a), another NRCS storm event surface water hydrologic model applied at a watershed scale, as the driving engine for all the hydrograph procedures (USDA NRCS 2005b),

WinTR-55 is a single-event, rainfall-runoff hydrologic model for small watersheds with multiple sub-areas that are homogeneous. It generates hydrographs from urban and agricultural areas, and the generated hydrographs are routed downstream through channels or reservoirs.

Storm Data

• NRCS storm data can be used.
• Rainfall return period (year)
• 24-hour rainfall amount (inch)
• Rainfall distribution type

Time of Concentration (T_c) Details

• Length (ft)
• Slope (ft ft^-1)
• Surface (Manning's n)
• Velocity (ft s^-1) for sheet, shallow concentrated, and channel flow types

24-hour Storm Duration

TR-55 uses only 24-hour storm duration; therefore, it is not applicable to the regions where the damaging storm duration is much shorter, such as 15 or 30 minutes.

Pre- and Post-Fire CNs

The user has to determine pre-fire and post-fire CN, which is a sensitive parameter; therefore, the estimated peak flow is subjective to users.

REFERENCES

U.S. Department of Agriculture, Natural Resources Conservation Service. (2005a, January 1-last update). Hydraulics and Hydrology: Tools and Models-WinTR-20 [Homepage of WinTR-20], [Online]. Available: http://www.wsi.nrcs.usda.gov/products/W2Q/H&H/Tools_Models/WinTR20.html [2008 October 24].

U.S. Department of Agriculture, Natural Resources Conservation Service. (2005b, January 1-last update). Hydraulics and Hydrology: Tools and Models-WinTR-55 [Homepage of WinTR-55], [Online]. Available: http://www.wsi.nrcs.usda.gov/products/W2Q/H&H/Tools_Models/WinTR55.html [2008 February 7].

U.S. Department of Agriculture, Soil Conservation Service. 1975. Urban hydrology for small watersheds. Technical Release 55. Chester, PA: U.S. Department of Agriculture, Soil Conservation Service. 91 p.

U.S. Department of Agriculture, Soil Conservation Service. 1986. Urban hydrology for small watersheds. Technical Release 55. Chester, PA: U.S. Department of Agriculture, Soil Conservation Service. 156 p.

 

USDA Forest Service - RMRS - Moscow Forestry Sciences Laboratory
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