An assessment of models and methodologies used in the design of detention facilities for small urban watersheds

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Virginia Tech

Recent efforts of Federal and local agencies to regulate nonpoint source pollution have resulted in an increase in the construction of water quality ponds. Such detention facilities help control nonpoint source pollution by capturing stormwater runoff and detaining the water, which provides time for suspended pollutants to settle out. In the process, flood peaks are typically attenuated, thus reducing the risk of flooding downstream. Detention ponds typically are implemented as land is developed from its natural rural condition to a more impervious urban condition.

The purpose of this research was to develop an improved methodology for the sizing of detention facilities for small urban watersheds. This research evaluated the tools used to determine the quantity of stormwater runoff from such watersheds, mainly through a detailed evaluation of computer models used to simulate rainfall and runoff processes. The EPA SWMM, HEC-I, and VTPSUHM are the computer models used in the analyses. Development of a watershed monitoring program on the Virginia Tech campus provided a foundation of gaged data used for calibration of computer models. The discussion on watershed monitoring presents information on the selection of equipment and installation locations, as well as potential problems in obtaining field data. Sensitivity analyses identified the parameters most sensitive to change for a highly impervious watershed. Finally, the rainfall distribution assumption and modeling approach in the design storm are examined. Each analyzed component of the detention facility design process will enhance the overall design of urban detention facilities.

stormwater, urban, hydrology, detention, runoff