Retrofitting Stormwater Systems with Low-Impact Development Techniques

Unusually heavy rains occurred in the spring and summer of 2007 and caused significant flooding across Oklahoma. One area, known as Babcock Basin—a 180-acre drainage basin in southwest Stillwater, Oklahoma—experienced flooding, and residents became very aware of the need for proper stormwater management. The city obtained funding through FEMA's Hazard Mitigation Grant Program (HMGP) to design a regional retrofit of the stormwater system to reduce flood risks. However, a condition of the grant was to use low-impact development (LID) techniques to the extent feasible, an approach that is atypical for Oklahoma. The area was nearly fully developed, primarily residential on quarter-acre lots with some institutional (church) property. Buying existing homes was not an option, therefore, the design team had to be creative in adapting LID elements to occupy a smaller footprint and serve a hybrid function of providing water quality benefits in frequent events and managing the runoff such that no structures would be inundated in a 1% annual chance (the so-called 100-year) event. In addition to the design challenges, there was a significant component of community outreach and education and the need to work with the property owners to gain acceptance of the project. This paper provides an overview of the design and addresses some of the inherent benefits, challenges, and other details associated with the project.