Flood Control in Toulmins Spring Branch Watershed through LID Practices

Abstract

Urbanization is known to cause increases in volume of stormwater runoff and peak flow rates, which leads to changes in natural flow regime and increases the likelihood of flooding. Conventional stormwater management practices mainly focus on reducing peak flow rates; surface runoff volume reduction has traditionally been ignored. Conversely, Low Impact Development (LID) practices seek to increase infiltration to reduce runoff volume and peak flow as close to the source as possible, and are generally considered to be a more sustainable solution for urban stormwater management. In this study, the effectiveness of two LID practices, rain barrel and permeable pavements, in mitigating urban flooding was tested within the 7.95 km2 Toulmins Spring Branch Watershed (TSBW) in southwest Alabama. The main motivation of studying the flooding problem in the TSBW was the frequent complains of its residents about chronic flooding. The EPA Stormwater Management Model (SWMM) was first calibrated with observed stage data at multiple sites then was used to identify the areas prone to flooding. Effectiveness of various LID practices in reducing peak flow and runoff volume at these areas were then explored with SWMM. Results indicate that LID controls can have considerable benefit for stormwater management by reducing runoff volume and peak flow rates, potentially returning watersheds to their natural flow regimes, thereby minimizing the flooding of urbanized areas. However, the effectiveness of LID controls, especially for the runoff volume, quickly diminish as the return period of the storms increase. Rain barrels were identified as the most economical and effective LID control within the TSBW drainage system.