US Army Corps of Engineers
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Prado Basin Feasibility Study

The U.S. Army Corps of Engineers (Corps) has completed a Draft Feasibility Report and Environmental Impact Statement/Environmental Impact Report (FR/EIS/EIR) for the Prado Basin Ecosystem Restoration and Water Conservation Integrated Feasibility Study. The Prado Basin study area, which includes a portion of the Santa Ana River downstream of the Prado Basin reservoir, encompasses portions of Riverside County, San Bernardino County and Orange County, California. The U.S. Army Corps of Engineers Los Angeles District is the lead Federal Agency and the Orange County Water District is the lead State Agency for this study. The Draft FR/EIS/EIR presents the plan formulation undertaken to develop feasible alternatives and also assesses the potential environmental impacts associated with implementation of the proposed project alternatives.

There are two components for the FR/EIS/EIR, ecosystem restoration and water conservation. The Water Conservation Plan would increase the current allowable temporary storage for water conservation to a greater volume behind Prado Dam and would reduce the flow release from Prado Dam during flood seasons. This would assist OCWD to reduce potential overdraft, reduce reliance on imported water and increase the local water supplies. Implementation of the water conservation measure would result in a slight regulation modification to accommodate a slightly higher temporary pool impoundment during the fall and winter flood season, which would be released at a rate that is optimal for groundwater recharge of aquifers associated with downstream reaches of the Santa Ana River. It does not compete with flood risk management objectives of the Santa Ana River Mainstem (SARM) project.

The Ecosystem Restoration Plan would restore the quality and function of aquatic, riparian, and transitional habitats within the study area, and address obstacles to regional wildlife movement for both terrestrial and aquatic species. A combination of the management measures would be implemented in select focal areas and would include invasive plant management, native plantings, channel restoration, non-native wildlife and aquatic species removal, sediment management, in-stream habitat features, and riparian edge management. Native species that would benefit from this restoration include the Federally-listed threatened or endangered Santa Ana sucker (Catostomus santaanae), least Bell’s vireo (Vireo bellii pusillus), southwestern willow flycatcher (Empidonax traillii extimus), western yellow-billed cuckoo (Coccyzus americanus occidetahs) and coastal California gnatcatcher (Polioptila californica californica).

The Tentatively Selected Plan with the proposed measures under the Plans are presented in full in Chapter 7 of the Draft FR/EIS/EIR. Refer to Chapter 3 of the Draft FR/EIS/EIR for detailed project descriptions of the proposed measures.