The Orange County Water District (OCWD) and the U.S. Army Corps of Engineers (USACE) reported the capture of 18.1 billion gallons of stormwater at Prado Dam between July 2025 and June 2026, the highest total since the 1940s. According to OCWD, the volume is enough to supply more than 110,000 households for a year and is valued at over $55 million. The milestone reflects a coordinated approach to operating the flood-control and water-supply infrastructure during an active winter driven by atmospheric rivers.
Water captured at Prado Dam flows downstream to OCWD’s recharge facilities in Anaheim and Orange, where it replenishes the Orange County Groundwater Basin. That basin supplies around 85 per cent of the drinking water for approximately 2.5 million people across north and central Orange County. During fiscal year 2025–26, Santa Ana River flows, including the captured stormwater, accounted for roughly 60 per cent of the district’s groundwater recharge.
OCWD attributed the record performance to Forecast-Informed Reservoir Operations (FIRO), a strategy that leverages advanced weather forecasting to track atmospheric rivers and adjust reservoir levels while maintaining flood protection. Under the dam’s original rules, Prado released water on a fixed seasonal schedule regardless of forecast conditions, leaving storage capacity unused when no major storm arrived. FIRO provides roughly five days’ notice of incoming systems, allowing operators to retain more water when no storm is expected or to pre-release in advance to clear space ahead of significant inflows, capturing supply that would otherwise be spilled for flood safety.
OCWD characterized the outcome as a demonstration of what can be achieved through innovation and strong interagency coordination. The district noted that FIRO enables greater local stormwater storage using existing infrastructure, reducing the need to construct new facilities while strengthening water reliability for the communities served.
Development of FIRO at Prado Dam stems from a partnership initiated in 2017 among OCWD, USACE and the Center for Western Weather and Water Extremes (CW3E) at Scripps Institution of Oceanography. A preliminary viability assessment published in 2021 found the approach feasible, and a final assessment completed in 2023 concluded it could add an average of 4,000 to 6,000 acre-feet of recharge per year, with potential to reach as much as 23,000 acre-feet in wet years.
Those findings informed a formal change in operations. In 2025, USACE approved a five-year minor deviation to the Prado Dam Water Control Plan, raising the conservation pool from 505 to 508 feet and adding storage capacity for close to 6,000 acre-feet of stormwater. The agencies are now working toward a permanent update to the dam’s water control manual that would formally incorporate FIRO into year-round operations.
Prado Basin is also a seasonal wetland supporting wildlife dependent on storm-driven habitat. To help balance flood control, water storage and environmental health, CW3E is developing a digital twin of the basin under OCWD’s direction, integrating meteorological, hydrological and ecological data to support future operational decisions. Prado is one of several dams where USACE and CW3E are testing forecast-informed operations, alongside Lake Mendocino on the Russian River and sites in the Yuba–Feather river system, as part of a broader effort to expand forecast-based reservoir operations across the western United States.