How are buffers modeled?

[aquarion]

How do you go about modeling a woodland buffer for treatment of stormwater? Take for instance a section of road sheet flows onto a designating buffer for stormwater treatment. How would a Reach be implemented using an infiltration rate/soil type....?

 

[psmart]

Although you could perform a separate hydrograph routing through the wooded buffer, the more common approach is to treat the woods as part of a subcatchment.

The woodland would typically have a low CN value, which would reduce the overall (weighted) CN value of the subcatchment, and thus reduce the runoff volume. (See the SCS runoff equation for details.)

The woods may also contribute to a longer time-of-concentration, which will delay the runoff and reduce the peak flow.