Rational Method Flow Length
Rational Method Flow Length
(OP)
Can you use the rational method if the overland sheet flow is greater than 500 feet for non-urban or 300 feet for urban areas?
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RE: Rational Method Flow Length
BTW, it doesn't matter which runoff procedure you use (Rational method, SCS, etc) the issue of the sheet flow length is the same.
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Rational Method Flow Length
RE: Rational Method Flow Length
Unless the surface is a perfect plane, sheet flow cannot persist for more then 50-300 feet. At some point the flow depth will start to vary and it will transition to a different flow regime. The sheet flow procedure is also limited to a flow depth of 1/10 foot.
See the National Engineering Handbook for complete details, including the length limitation.
https://directives.sc.egov.usda.gov/OpenNonWebCont...
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Rational Method Flow Length
for example, see the method below which does not consider sheet flow at all:
RE: Rational Method Flow Length
Peter Smart
HydroCAD Software
www.hydrocad.net
RE: Rational Method Flow Length