Modeling Play areas with wood chips that has underdrain

[Luii]

Any idea what would be the initial abstraction for a wood chip play area? I am modeling it with an under drain system. What can would be a good curve number substitute surface to model the wood chips?

 

[Twinkie]

Is this your actual storage BMP? Or just a portion of your drainage area? If you are just trying to figure out the runoff rate and volume, the CN as you mentioned, I would likely use some kind of woods/grass combo.

Obviously, any storage volume within the wood chips themselves would be highly variable based on a current water content, but there should be a constant void ratio within the wood chip bed itself. What that is (50%) I really have no idea. Interesting question.