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Trampas Canyon Dam and Reservoir


Geotechnical Project


Santa Margarita Water District’s new Trampas Canyon Dam and Reservoir has a capacity of 1.6 billion gallons of water – enough water to fill 2,500 Olympic-size swimming pools – and is the largest surface water reservoir in south Orange County and the first reservoir built in decades. The project features three dams that reach 216 in height and a reservoir that is 3,000 feet across and 80 feet deep. The project helps the District to use 100% of our community’s wastewater, building regional sustainability and resiliency. The project will allow the region to save drinking water supplies by using recycled water to irrigate parks, medians, and common area landscape. The reservoir may also one day provide the District and its partners with the opportunity to reuse the recycled water for direct or indirect potable purposes.
Santa Margarita Water District (SWMD) has constructed south Orange County’s largest reservoir and the first reservoir built in decades. The Trampas Canyon Reservoir is a recycled water reservoir that provides seasonal and operational storage for the District’s existing and proposed recycled water system. The proposed reservoir supplies irrigation demands for Talega Ranch, Ladera Ranch, Village of Sendero, Village of Escencia, the proposed Ranch Plan development, City of San Juan Capistrano and other existing irrigation demands within south Orange County. Recycled water is supplied by the Chiquita Water Reclamation Plant (CWRP) and will be supplemented by other non-domestic water supply sources and reclamation plants. In addition, the proposed reservoir will provide storage for other recycled water purveyors in south Orange County.
SMWD has reconfigured the existing Trampas Canyon Dam and Reservoir to convert it from a tailings retention facility to a recycled water supply reservoir. The dam and reservoir were reconstructed on 177-acres of property to create a 1.6-billion-gallon recycled water reservoir. The proposed Trampas dam reconfiguration project includes raising the existing earthfill embankment (Main Dam), constructing two saddle dams (East and West Saddle Dams) and appurtenant facilities (i.e. an inlet/outlet structure, inlet/outlet tunnel and pipeline, spillway, roadways, and a multi-zone booster pump station). The reconfiguration for the proposed Trampas Canyon Reservoir includes the following features:
• Raising the existing Main Dam to increase reservoir capacity and provide the minimum freeboard required by the California Department of Water Resources Division of Safety of Dams (DSOD);
• Removing a portion of the existing Main Dam crest to allow the proposed raised dam core to tie into the existing core;
• Adding a downstream buttress and filter/drain layers to mitigate historical deficiencies associated with the existing Main Dam (e.g., seepage, stability);
• Constructing an inlet/outlet structure and associated pipeline with gravity outfall for reservoir emergency drawdown;
• Constructing a new, higher capacity, spillway;
• Constructing two saddle dams; one at the existing Saddle Dam (East Saddle Dam) and the other would be required due to recent road cuts at the west end of the reservoir (West Saddle Dam).