BMP Trains - Provided Retention Depth

[Afrexico]

With the BMP Trains program in Florida, under the Retention Basin treatment option under "2. Enter Treatment" it asked for "Provided Retention Depth (in over Catchment)". May someone elaborate on what it is asking for. I took it as the actual elevation difference between design pond bottom and top, but the statement in parenthesis is making me question that understanding. First time, I am using BMP Trains. Thanks.

 

[TerryScan]

I have no knowledge of the program you are speaking about, but it sounds like one should take the Retention Volume (Vr) and divide it by the catchment Area (A) to get the desired Depth (over catchment). (This would equate to runoff volume)

Example
Vr = 10,000 ft and a 2.0 ac. catchment:

10,000 cf / (2*43,560) = 0.1148 ft = 1.38 inches depth