Curve number for large gravel area

[briandestefano]

I will be preparing a stormwater management report for an industrial site (new construction) with a large gravel area. The area will be approximately 5 acres with a 12" depth. I was wondering what curve number you guys think would be best to use. I have worked on other projects before where I was instructed to use 98, the same as asphalt paving, and other times it has been lower.
Being that so much of the site will be covered with asphalt and buildings I would like to use a lower curve number, that is still accurate, for the gravel storage and parking areas. Any help you guys can give is much appreciated

 

[bltseattle]

Check if it's in the city/county or state drainage manual/guidelines. If not, you could use the TR-55 values:

Gravel (including right-of-way),
HSG A/B/C/D RCN = 76 85 89 91 respectively

 

[cvg]

depends on what type of gravel and the amount of compaction or other treatment.

open graded gravel would have much less runoff than dense graded - compacted road base material. If your void space in the (open graded) gravel is 30%, you could infiltrate approximately 3.6 inches of rain before you get any appreciable amount of runoff at all. With the dense graded aggregate (road base), I would agree it is about the same as asphalt. Especially if you have 95% compaction or if you use any sort of binders to stabilize dust, you could approach the 98 value.