Detention in lower sections of a watershed

[chaa]

It appears that detention basins located in the lower sections of a watershed are not necessary. They might even be detrimental because of peak discharge increase.
For a 12 square mile watershed what kind of analysis can be performed in order to identify the lower section of the watershed where the construction of a detention basin is not required/recommended?
Can anyone help?
Do you know any literature describing the steps for such a task?

 

[sam74]

I have done a few. Usually take a quad map or GIS, if enough is available, and delineate the entire watershed. You usually need to be somewhat close to the creek/river you delineate. Perform drainage calcs using NRCS method with any of a various number of softwares. Then locate your site on the quad or GIS map. Perform pre and post drainage calcs for your site. Compare time to peak of your site with that of the entire watershed. If time to peak of your site is earlier than that of the watershed as a whole then you are in effect lowering the peak of the watershed by not detaining (usually).