Real-Time Control and Bioretention: Implications for Hydrology

Bioretention practices have been developed to restore natural hydrologic regimes by reducing runoff volume and mitigating the peak flows of urban runoff. This is critical as cities encounter more extreme weather and their aging infrastructure is left ill-equipped to manage new stormwater management challenges. Functional improvements to bioretention through the use of real-time control (RTC) systems may allow more responsive system adjustments to manage incoming runoff volumes; however, minimal research has been performed to understand how various RTC schemes affect hydrologic partitioning and promote runoff volume reductions. A 6-week column study was conducted in which the water balances for static bioretention designs [i.e., free draining (FD) and internal water storage (IWS)] were compared against those of two RTC designs that focused on either regulating soil moisture (SM) or maximizing internal storage volumes (VC). Of the two RTC designs, the SM configuration showed the most storage capability (18%) and the lowest rate of bypass (7%) compared to the VC configuration that showed storage and bypass rates of 11% each. The FD and IWS configurations exhibited storage at 9% and 16% and bypass at 2% and 11%, respectively. This shows the potential for RTC to meet multiple, sometimes conflicting, objectives; in this case, volume reduction and bypass minimization. Correlation analysis revealed strong relationships between storm size and effluent volumes, but no correlation with seepage. Future research into the use of RTC for bioretention should include variable rainfall intensity in lab-scale studies to better understand flow dynamics over time. Studies should also be conducted in field-scale experiments to understand the larger practical implications of their design and implementation.