The Regional Stormwater Detention Concept in Urban Drainage System.
This chapter uses a case study to demonstrate a regional stormwater detention concept which can be applied to solve flooding problems in urban areas. The stormwater detention concept has been implemented for more than thirty years in the United States with some success. However, local stormwater regulation and permitting lead to small detention ponds individually provided without a regional prospective. Individual detention facilities may successfully control the local peak flow. Nevertheless, the downstream reach may still suffer from flood damage due to the surface runoff rate and volume that results from increased regional addition of impervious areas. The Lincoln Creek watershed in Milwaukee, Wisconsin has been selected for this case study. Approximately 1500 residential homes experienced flood damage in this nineteen square mile watershed. The Army Corps of Engineers computer programs, HEC-1 and HEC-2, were utilized to analyze detention and watercourse improvement alternatives.
Evaluations of potential detention or retention locations preceded estimates of storage volumes at each site. Various channel improvements, including different shapes, dimensions, and bank protection materials, were evaluated on a reach-by-reach basis. Iterative HEC- I and HEC-2 techniques served to evaluate carefully-selected alternatives with channel storage that would mitigate the existing flooding problems and minimize adverse impacts downstream. The preparation of hydrographs at each sensitive location facilitated easy graphical comparisons. The preliminary results show that, by using the combination of retention and detention ponds throughout the project area and various channel improvements, existing flood-prone areas can be protected from damage by the 100-year storm event. This regional approach ensures that solving a problem at one place does not create a problem somewhere else.
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