Forecast Informed Reservoir Operations: Prado Dam

FIRO is a reservoir-operations strategy that better informs decisions to retain or release water by integrating additional flexibility in operation policies and rules with enhanced monitoring and improved weather and water forecasts (American Meteorological Society; 2020). Since 2014, CW3E and federal, state, and local partners have developed, tested, and implemented FIRO at reservoirs across the Western United States. FIRO is now being assessed nationwide.

Water stored behind Prado Dam

PROJECT STATUS

Temporary FIRO Implementation

Multi-Year Deviation in place

OVERVIEW

Prado Dam is operated by the US Army Corps of Engineers (USACE) primarily for flood risk management, with water conservation as a secondary purpose. USACE works in partnership with the Orange County Water District (OCWD), which has been capturing and recharging stormwater from the Santa Ana River since 1936.

Together, these agencies manage releases from the Dam to facilitate recharge of the Orange County groundwater basin, which provides 85% of the water supply for 2.5 million people across north and central Orange County, while simultaneously managing flood risk for downstream communities. These collaborative operations sustain the Prado Basin, a seasonal wetland ecosystem that supports abundant wildlife and critical habitat for a federally endangered migratory songbird, the Least Bell’s Vireo.

The motivation for implementing FIRO at Prado Dam is to maximize water conservation for groundwater recharge in the Santa Ana River Basin while maintaining robust flood risk management for downstream communities in Orange and Riverside Counties. After conducting primary and final viability assessments, FIRO has been in place at Prado Dam since February 2025, allowing operators to store more water behind the dam than previously permitted through a USACE-approved deviation in operations, raising the conservation pool from 505 feet to 508 feet. FIRO partners are exploring raising the conservation pool to 510 feet, alongside a formal USACE Water Control Manual update to codify the new operating rules by 2030.

FIRO PROGRESS

Timeline of FIRO progress at Prado Dam

Forecast Informed Reservoir Operations implementation progress at Prado Dam. Green circles indicate completed milestones, blue circles indicate milestones in progress, and amber circles indicate upcoming milestones.

KEY ACHIEVEMENTS

628 ac-ft

of additional water stored at Prado in Water Year 2025-2026

2.5 Million

People across north and central Orange County benefit from the additional water supply

Cross-sector partner organizations working collaboratively to implement FIRO at Prado Dam

Nesting Least Bell’s Vireo. Photo courtesy of OCWD

Prado Dam Digital Twin

A unique consideration for FIRO at Prado Dam is the Prado Basin, a seasonal wetland ecosystem that depends on stormwater capture during the wet season. The Basin supports an abundance of wildlife that depend on the critical riparian habitat, including the federally endangered migratory songbird, the Least Bell’s Vireo. To better understand and monitor the ecology of the Prado Basin, CW3E is developing an innovative digital twin under OCWD’s direction and in close coordination with environmental resource agencies. The Prado digital twin integrates diverse meteorological, hydrological, and ecological datasets with the potential to support operational decisions aimed at balancing flood control, water storage, and environmental health.