Investigation of Highway Stormwater Management Pond Capacity for Flood Detention and Water Quality Treatment Retention via Remote Sensing Data and Conventional Topographic Survey

Abstract

Stormwater management ponds are common best management practice (BMP) and green infrastructure (GI) for flood attenuation and water quality treatment in highway projects. Originally designed to provide storage volume for flood detention, stormwater ponds today often employ additional retention volume at pond bottom in a hope to improve water quality via sedimentation and other pollutant-removal mechanisms. It is commonly assumed that sediment accumulation and topographic variations (such as erosion, channelization, and in-pond plant growth and decay) over time often decrease the capacity of stormwater ponds. However, differences between design capacities and field capacities over time have never been verified and quantitatively analyzed before. This study presents such analysis using conventional topographic survey techniques and remote sensing data (topographic light detection and ranging digital elevation model [LIDAR DEM]) for 10 highway stormwater ponds along Interstate Highway-95 (I-95) systems in Baltimore City, Cecil County, and Harford County, Maryland, United States, with facility service life ranging from 14 to 26 years (1990–2015). Data derived from LIDAR DEM were compared with those from topographic survey; the LIDAR DEM data appear to be effective in measuring flood detention capacities and identifying silted ponds, but not in estimating the remaining retention volume for water quality treatment. Data from topographic survey indicate that the total volume in the ponds was relatively unchanged compared with the design, with increases in some instances. The increase typically occurred at the pond’s upper stages. Nonetheless, the water quality treatment capacity at pond bottom (wet pool volume) was drastically less (up to 100% of the design). As current maintenance practice of stormwater ponds relies heavily on visual inspection, the storage volume variations are often overlooked. As such, the findings prompt uncertainty on the long-term effectiveness of watershed implementation plan and models in the Chesapeake Bay watersheds, as many of them depend on wet pool volume design in BMP and GI.