Depth of flow on parking lot

[DPAJR]

I am trying to figure out how to determine the depth of flow across an asphalt parking lot (sheet flow or shallow concentrated runoff). I can calculate the accumulated runoff no problem but I am not sure how to get the max depth at any one instant.

Thanks

 

[jgailla]

The USDA (United States Dept. of Agriculture) has a Technical Release 55 (TR-55, Urban Hydrology for Small Watersheds) which is commonly used to determine runoff on small sites (<100 or 200 acres).
Sheet flow by definition from the TR-55 is "0.1 foot or so".
Sheet flow is assumed to take place up to a travel length of 300 feet, but could be less, especially in a parking lot.
You could take the peak flow, determine the velocity, and then get the area of flow. If you have an inverted crown type parking lot towards the inlet, you get the area of the triangle that produces the peak flow and solve for the depth.

 

[froude]

you can probably use the peak flow you've calculated in conjuntion with a normal depth (Manning's eqn) calculation to get a reasonable estimate.

 

[DPAJR]

Thanks for the suggestions. That's what I will do.

Thanks,

 

[gte959s]

jgailla (Geotechnical) has the right answer. You really dont have a sheet flow depth over 0.1'. You would have some sort of shallow concentrated flow that would be produced at some point.