Using SCS on small drainage sheds (In conjunction with thread162-13255)

[AJB1262]

In conjunction with thread162-13255

I have a comment from a local reviewer indicating a preference for rational method in a small development site over the SCS method. While the SCS method is more suited for larger watersheds, we routinely use it for small sites because the state agencies require it's use for water quality volume calculations.

There is nothing in the local ordinance which precludes the use of the SCS method in smaller watersheds (under 20 acres).

In my experience the SCS method would yield more conservative storm routings as it is distributed over a longer storm duration.

Any opinions or thoughts appreciated. It is my belief all these methods are approximation and without a detailed study of predevelopment conditions of a watershed (gaging, monitoring and statistical analysis) that's all they are. It's funny how one or another method has been entrenched into a reviewer's mind as being "gospel" when the truth it is engineering judgement and part of the liability assumed by the sealing engineer providing the design.

 

[psmart]

I think you covered it pretty well. From a technical standpoint there is nothing wrong with using the SCS method for very small sites. In fact, it has many advantages over the Rational method.

Peter Smart
HydroCAD Software

http://www.hydrocad.net