Sukut Construction Awarded Syphon Reservoir Improvement Project to Strengthen Southern California’s Water Resilience

Sukut Construction has been awarded a contract by the Irvine Ranch Water District for the Syphon Reservoir Improvement Project, one of Southern California's most significant water infrastructure upgrades in recent years. The $214-million project will substantially increase the existing reservoir’s recycled water storage capacity from 578 acre-feet to 5,000 acre-feet, strengthening the community's long-term water resiliency. 

Once completed, the expanded reservoir will provide a reliable source of recycled water for agricultural irrigation, environmental uses, emergency response efforts, and future regional water needs. The increased storage capacity will also help reduce the demand for potable water resources by maximizing the use of recycled water throughout Irvine and its surrounding communities. In addition, the reservoir will serve as an important resource during wildfire emergencies, providing readily available water for firefighting operations without drawing from drinking water reserves. 

Delivering a project of this magnitude requires extensive planning and coordination with the project stakeholders to execute the complex construction operations and meet the rigorous standards of California’s Department of Water Resources Division of Safety of Dams. Sukut will degrade the existing dam currently standing at 59 feet tall to competent bedrock to meet the foundation objectives prior to embanking to a new height of 138 feet to support the 1.6-billion-gallon storage capacity. Prior to the degradation of the existing dam, a stream diversion system designed to withstand a 500-year storm event will be installed upstream to support construction and protect downstream communities. Extensive dewatering operations and both temporary and permanent erosion control measures will be installed to protect water quality and surrounding ecosystems throughout construction. 

The scale of earthwork associated with the project is substantial. Crews will excavate and stockpile approximately 580,000 cubic yards of material from the existing dam and an additional 1.6 million cubic yards from the proposed reservoir basin for use in the new embankment. Construction of the new dam will require extensive core and shell foundation treatment prior to placing approximately 2.14 million cubic yards of zoned embankment material, carefully engineered and compacted to meet stringent performance standards. To ensure long-term dam safety and performance, the embankment will incorporate advanced instrumentation, including piezometers, settlement monitoring systems, and accelerographs, to provide engineers with real-time data for decades to come. Additional foundation improvements include construction of a 1,500 linear-foot cutoff wall beneath the dam foundation and a two-line grout curtain along the dam’s axis, which requires approximately 55,000 linear feet of drilling and grouting to reduce seepage through the underlying bedrock. The project also includes the installation of 137,000 cubic yards of specialized filter and drain aggregates designed to manage internal water flow within the dam structure. 

Beyond the dam itself, the project includes significant environmental restoration and improvements to hydraulic infrastructure. New riparian woodland habitat will be established by planting native trees and vegetation, helping stabilize soils, enhance wildlife habitat, and improve the surrounding environment. 

The hydraulic infrastructure will feature new inlet and outlet works facilities, including approximately 1,240 linear feet of 42-inch polyurethane-lined and cement-coated steel pipe encased in mass concrete and secured with rock anchors. Supporting facilities include a new dam control building, a treatment building with a foundation supported by deep-spoil mixing, an emergency outlet structure, and a spillway consisting of a tunnel with 60-inch steel pipe from the inlet structure to an energy dissipator, and then a junction structure connecting key components of the system. Additional work includes construction of both wet and dry site utilities, access roads, operational facilities, public trails, and extensive landscaping improvements that will integrate the upgraded reservoir into the surrounding community. 

The Syphon Reservoir Improvement Project stands as one of the most ambitious water-storage upgrades in the region's recent history. Upon completion, it will significantly expand recycled water storage capacity, strengthen drought resilience, support emergency response efforts, and help secure Southern California's water future for decades to come.