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The Soil Conservation Service hydrologic method is widely used by engineers and hydrologists
for analyses of small urban watersheds. This method is based on extensive analytical
work using a wide range of statistical data concerning storm patterns, rainfall-runoff
characteristics and many hydrologic observations in the United States.
The SCS method can be applied to urban drainage areas of any size. The major parameters
required to calculate a runoff hydrograph with the method include the rainfall distribution,
runoff curve numbers, time of concentration and drainage area. For detailed information
regarding the SCS method and the TR-20 program, the user is referred to the following
NRCS publications. These can be obtained from the Natural Resources Conservation Service
at http://www.wcc.nrcs.usda.gov/. They are:
NEH-4: "Hydrology," Section 4, National Engineering Handbook
TR-20: Computer Program for Project Formulation, Hydrology
TR-55: Urban Hydrology for Small Watersheds
TP-149: A Method for Estimating Volume and Rate of Runoff in Small Watersheds
The HEC-HMS programs can be downloaded from the US Army Corps of Engineers website
at http://www.hec.usace.army.mil/. Refer to Section 8.2.3 for information regarding watershed hydrologic models that are maintained by the
City. These models may be requested by the public and used as the basis for drainage
analysis where applicable. Any results based on models obtained from the City must
be certified by a Texas Licensed Professional Engineer.
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