Curve number - Rip rap protected slope

[clarkpe]

I am designing a stormwater system for a proposed development at a site that is a former gravel pit with steep slopes. The geotechnical engineer wants to line the surface of some of the slopes with rip rap for stabilization. The slope in one area is 2:1 and 120-ft long. My question is what should I use for a CN and time-of-concentration?
Thanks

 

[psmart]

I would base the CN value primarily on the underlying soil, since that's where the infiltration and retention occurs.

For the Tc, you could use shallow concentrated flow with an appropriately low velocity factor.

Otherwise, ask the reviewing agency what they would recommend/accept.


Peter Smart
HydroCAD Software

http://www.hydrocad.net