Restoring Predevelopment Hydrology with Smart Stormwater Controls in Aiken, South Carolina

Abstract

For decades, large quantities of stormwater runoff from the City of Aiken flowed at destructive velocities (exceeding 5 ft/s) into the Sand River, deeply eroding the channel in the downstream Hitchcock Woods. From 1990 to 2015, the City of Aiken commissioned several consultants to produce over a dozen studies to investigate viable solutions for the destructive erosion. Upon the recommendation from a collaborative Stormwater Task Force, the City of Aiken approved a stormwater implementation plan in 2018 which recommended 20 capital improvement projects sized to capture 58 ac-ft of stormwater in order to restore the river’s predevelopment hydrology, with a goal of reducing stormwater velocities in the Sand River to reflect design considerations in the National Engineering Handbook (between 2.0 ft/s for fine sand channels and 4.0 ft/s for coarse sand channels). In November 2023, the City of Aiken completed construction on two underground detention vaults with a total storage volume of 25 ac-ft. These vaults were designed to capture stormwater runoff before it enters Hitchcock Woods and infiltrate as much stormwater runoff as possible; any additional stormwater will be released at a reduced flow rate compared to existing conditions. The 10-year, 24-hour storm event was selected to size the vaults because it was an achievable metric given numerous constraints such as available land, impacts to existing infrastructure and environmental resources, and available funding. The 10-year event also corresponded to typical stormwater requirements for new development. The vaults utilized the largest height, 15 feet, available for precast underground storage vaults in the marketplace. In addition to providing stormwater management below ground, a new public park was constructed on top of the buried vaults to be used as a gateway between the Hitchcock Woods and the City of Aiken.