Using exfiltration in ditch

[Jmeng1026]

How do I take into account exfiltation in a grass ditch while the stormwater is being routed to a detention basin? Some of the stormwater runoff will percolate into the ground while it flows through the ditch which would equate to less water reaching the basin.

 

[psmart]

If you are modeling the ditch as a reach you can use the "Inflow Loss" parameter. However, it's fairly uncommon to allow for exfiltration through a grass ditch. Any exfiltration capability is generally overwhelmed by all but the smallest storm events. The exception would be a stone-lined channel that is designed specifically as an infiltration area, but that's another discussion.

Also please see

http://www.hydrocad.net/exfilt.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[beej67]

If the ditch is just grass, then the infiltration you'd experience in the ditch will probably be accounted for in the initial abstraction of the hydrology node. Basically the curve number gives you all the losses the ditch is going to experience unless the ditch is enhanced in some way.

If the ditch is an "enhanced swale," or similar feature which is specifically designed to capture and infiltrate water into the ground, then enter it into your model as a node or series of nodes.

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

http://www.campbellcivil.com