Curve number for gravel parking area

[DPAJR]

I need to find the curve number for a couple of gravel parking lots. All I can find in the curve number tables of Hydrocad and TR-55 is gravel with right of way included. The numbers for that have to be lower than for just plain gravel pavement.

I am guessing close to 98 but I don't want to overdo it either.

Thanks

 

[psmart]

It's unfortuntate the the SCS didn't publish a specific value for gravel road surfaces excluding the right-of-way.

However, if you examine the TR-55 values for gravel road with ROW, they appear to be based on 30% gravel with CN=96 and 70% "open space" in poor condition. So 96 would be a reasonable value to use for the gravel alone.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[SMIAH]

I'd take 98 for peak flow estimation.
If it's for a volume of runoff though, you may want to choose something little lower and this will probably give you an head ache.
It's not an exact science...

 

[beej67]

I'd go with Peter's answer.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[Ryb01]

"Gravel" parking lots don't necessarily stay "gravel" for extended periods of time. A higher CN, as the forum has suggested is reasonable.

 

[Drew08]

I'd think about the kind of traffic that will be on it as well. A "B" HSG sub-grade might compact to a "C" or "D" (essentially CN 98)if there is heavy construction traffic like a haul road, but might not if the lot is intended for long-term parking of small cars, or empty truck containers (closer to CN 96).

Same issue if the lot is constructed on compacted fill as oppose to natural ground.