Increasing Stormwater Capture and Recharge Using Forecast Informed Reservoir Operations, Prado Dam

Abstract

The United States Army Corps of Engineers (USACE) operates Prado Dam in southern California for flood risk management and to capture stormwater for groundwater recharge. USACE and the Orange County Water District (OCWD) have collaborated for over 30 years to temporarily store Santa Ana River (SAR) stormflow at Prado Dam for groundwater recharge in the Orange County Groundwater Basin (Basin). USACE, OCWD, and other stakeholders are assessing Forecast Informed Reservoir Operations (FIRO) at Prado Dam as a new operational approach to capture additional supplies of SAR water for groundwater recharge without affecting Prado Dam's primary flood risk management purpose. Many dams, including Prado Dam, do not directly incorporate precipitation and streamflow forecasting in their operations. FIRO is an innovative research and operations partnership that uses weather forecasting, streamflow modeling, and watershed monitoring to help water managers selectively retain or release water from reservoirs in a manner that reflects current and forecasted conditions. A recently completed study, called a Preliminary Viability Assessment of FIRO at Prado Dam, determined that increased stormwater capture, beyond the current program, is viable subject to completion of additional studies. The ultimate increase in stormwater capture is anticipated to largely be a function of community and environmental tolerance for more frequent inundation rather than operational constraints of the dam. FIRO is a promising approach to operating Prado Dam that can increase SAR stormwater capture for recharge to the Basin, reducing the need for imported water and contributing to sustainable groundwater management.

Stress Testing California's Hydroclimatic Whiplash: Potential Challenges, Trade‐Offs and Adaptations in Water Management and Hydropower Generation

“…On the other hand, when short‐term forecasts indicate no significant rain event is expected, operators could retain flood waters above the original flood control curve, which can lead to greater reliability for water supply and ecosystems, power generation, and managed aquifer recharge (MAR), while maintaining existing flood control capabilities (Cobb et al., 2023; Ralph et al., 2014; Woodside et al., 2022; Zarei et al., 2021). Moreover, the use of flood waters for MAR (Flood‐MAR) (Kocis & Dahlke, 2017) has been adopted to address the widespread groundwater overdraft in the state (Leahy, 2016), as required by the Sustainable Groundwater Management Act (Hanak et al., 2019), especially when using the existing irrigation infrastructure for on‐farm recharge (Ag‐MAR) (Levintal et al., 2023).…”