Evaluation of retention basins and soil amendments to improve stormwater management in Florida

The research presented here addressed two aspects of stormwater prevention. The first aspect was the elimination of stormwater through retention basins. Infiltration rates were measured by Double Ring Infiltrometer (DRI) within 40 basins in Alachua, Leon, and Marion counties. Measured rates were compared to designed rates to determine whether basins were operating as designed. The 40 basins were equally divided between residential and Florida Department of Transportation land uses. Texture analysis was also performed on soil samples taken from each infiltration location; soil types ranged from sand to sandy clays. Eleven of the 40 basins were also instrumented with monitoring equipment to measure drawdown rates. Three basins did not adequately store water to determine drawdown rates. However, 6 of the remaining 8 basins had drawdown rates less than DRI rates while the other 2 basins were not statistically different from DRI rates. This indicated that subsurface conditions were controlling basin drawdown rates. DRI rates frequently varied by at least an order of magnitude within basins. Based on DRI rates, 16 (40%) basins had rates less than their designed rates, 10 (25%) had rates equal to their designed rates, and 14 (35%) basins had rates greater than their designed rates. Additionally, FDOT basins had a higher proportion of basins with greater DRI rates than residential basins and coarser basins were also more likely to have DRI rates greater than designs. Greater size and diversity of vegetation resulting from less frequent maintenance in FDOT basins may have resulted in a higher proportion of sites with rates equal to or greater than designs.;The second aspect is stormwater generation. Traffic during construction has been shown to compact soils, resulting in reduced porosity and infiltration rates and increased runoff. In agricultural settings soil amendments have been found to counteract compaction effects. Two soil amendments (compost and fly ash) were evaluated for mitigating compacted soils. Forty-two lysimeters were filled with two soils (Orangeburg Sandy Loam and Arredondo Fine Sand) overlaying a drainage layer of quartz stone. Runoff was directed into collection tanks and volumes were recorded. The soils were compacted to levels representative of observed levels found in North Central Florida based on bulk densities and infiltration rates. Runoff and leachate samples were analyzed for nitrogen species and orthophosphorus. Incorporating fly ash did not significantly reduce runoff. Tillage to at least 10 cm decreased runoff compared to compacted soils. However, adding compost treatments did not significantly reduced runoff compared to just tillage.