Survey of Retention Basin Hydraulic Performance in Florida

Abstract

Retention basins have commonly been utilized to reduce or eliminate runoff in Florida. Forty retention basins were included in a field study to determine whether basins infiltration rates were significantly different from designs by comparing current hydraulic performance to design infiltration rates. Basins included in the study ranged in age from less than one year to over twenty years old. Basin locations were divided between Leon, Alachua, and Marion Counties in Florida, while watershed land uses were equally divided between Florida Department of Transportation and residential developments. For each basin, typically six test sites were selected for infiltration rate measurement using double ring infiltrometers. In addition, a surface soil boring was collected from each of the test sites to analyze soil texture, bulk density, porosity, gravimetric water content, and organic matter content. Multiple cone penetrometer profiles and soil moisture readings, using a time domain reflectometer, were also taken from each of the six test sites to determine existence of a potential infiltration limiting sublayer. Eleven of the basins were subsequently instrumented with water level recorders, tipping bucket rain gauges and manual rain gauges to determine draw down rates from various rainfall events. Draw down rates were then compared to double ring infiltrometer and design rates. Based on double ring infiltrometer measurements, 16 sites had infiltration rates that were significantly (p < 0.05) less than design rates, while 14 were significantly greater than design rates and the remaining 10 were not significantly different from design rates. Preliminary analysis of five monitored basins shows that four had draw down rates approximately one order of magnitude below designs.