Evaluation of Alternative Stormwater Detention Policies

Mathematical modeling is a quick, inexpensive and effective means of evaluating existing stormwater detention policies and examining alternative policies. The model was then calibrated with data collected from a watershed located in Montgomery County, Md. The data base included measured precipitation, and both sediment and flow into and from the detention basin. Model studies indicate that many existing SWM policies do not meet the intent of SWM because they ignore the volume- duration frequency concept that has long been used in hydrologic design. SWM policies often fail to specify a duration for detention basin design and limit the design frequency to a single return period. A detention basin that is designed using a policy based on a single return period will not limit the entire flood frequency curve to that of the before-development conditions, and thus the policies do not satisfy the intent of a SWM. Also, less costly designs are possible if both basin volume and outlet characteristics are considered simultaneously.