Evaluating the Water Quality and Hydrologic Performance of Passive and Active Release Systems Retrofitting Rainwater Harvesting Cisterns

Abstract Submission: Previous research has demonstrated passive and active release mechanisms retrofitting rainwater harvesting cisterns can mitigate stormwater runoff. However, passive release systems can discharge during storm events and contribute to runoff. Additionally, active release systems typically consist of real-time control that require proprietary software and components that can be expensive to obtain. To address these concerns, Clemson University is currently evaluating the hydrologic and water quality performance of a non-proprietary, active release mechanism that retrofits a cistern’s passive release system. The active release mechanism consists of a residential irrigation controller, rainfall and soil moisture sensors, and an actuator valve. The controller and sensors signal to the actuator valve to close the passive release orifice during storm events and when the soil is too saturated to infiltrate the discharge. The performance of the active release system (e.g., peak flow reduction, percent bypass) will be compared to a cistern retrofitted with traditional passive drawdown. Both 7,949 liters cisterns have been sized to capture 87% of the average annual runoff, and each cistern will receive runoff from a sloping metal roof with an area of 97 square meters. This presentation will include water quality results (nutrients, total suspended solids, microplastics) collected from the inlet and release mechanisms as well as hydrologic data from each cistern.

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