Small Urban Watersheds 1

[TCE2009]

Does HydroCAD have any lower limtis on the watershed size? For urban watersheds less than 5 acres, I have been told the SCS TR-20 Method may not be reliable and a rational method should be used. I do not see any hints or errors when running small watersheds.

 

[psmart]

HydroCAD does not impose any lower limits on the watershed size or Tc, so this is really a matter of using the most appropriate methodology.

Some localities specify the Rational method for small waterersheds, while others specify the SCS/NRCS method regardless of size.

I generally recommend SCS over Rational whenever it is accepted by local regulations, partly because it provides a complete runoff hydrograph that is required for volume-sensitive calculations, such as detention ponds.

For details please see

http://www.hydrocad.net/rational.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net