Sites Reservoir Project – Alternatives Analysis and Feasibility-Level Design of Regulating Reservoir
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Project Objective

The Sites Reservoir Project includes a new 1.5 million-acre-feet reservoir to be situated within the eastern margin of the California Coast Ranges, along the west side of the Sacramento Valley. The facility will receive and release water through a system of new pipelines and existing canals connected to the Sacramento River, with operations driven by two pumping plants, which will also serve as power generating plants. At the heart of this system will be two regulating reservoirs, the Funks Reservoir and the Terminal Regulating Reservoir, where the new pipelines will intersect the existing canals. The regulating reservoirs allow for concurrent operational management of the canals and of the pumping and power-generating plants that control flows in and out of Sites Reservoir. Funks Reservoir is an existing reservoir, which will be modified, and the Terminal Regulating Reservoir is a new reservoir.

Geosyntec’s Scope of Services

Geosyntec is the project lead for the configuration and design of the two regulating reservoirs. Geosyntec performed feasibility development, evaluation, and design for the reservoirs, including coordinating with stakeholders, identifying objectives, and developing design criteria; conceptualizing, creating, evaluating, and selecting layouts and configuration alternatives; conducting feasibility-level analysis and design for the reservoirs and appurtenant features; and preparing design documentation, quality review documentation, quantities and cost estimates.

For the Funks Reservoir, impounded by an earthen embankment dam, Geosyntec planned and designed modifications to increase its capacity and reshape its configuration. Sediment removal approaches were evaluated, including dredging methods and in-the-dry excavation. Geosyntec developed and evaluated different excavation plans, to modify the bottom of the reservoir (below sediment removal). Layouts and configurations were developed also for two temporary cofferdams to facilitate construction of new pipelines and a new pumping/generating plant. Along with construction sequencing and methods, Geosyntec identified, evaluated, and selected stockpile areas and haul routes to accommodate sediments and excavation spoils.

For the Terminal Regulating Reservoir, a planned new off-stream reservoir, Geosyntec developed the plan and designs, including performing hydraulic analyses for design of the emergency spillway. The reservoir will be developed as a combination of shallow excavation across the floor of the reservoir and construction of a perimeter earthen embankment dam, approximately 2.3 miles long. Geosyntec evaluated alternative methods of remediating the adverse soil conditions (soft clays and silts and significant zones of liquefiable sands), identifying cement deep soil mixing as the preferred method of ground improvement, and developed feasibility-level designs and cost estimates.

Notable Accomplishments

Geosyntec remained flexible and agile, rapidly responding to schedule compressions, repeatedly adjusting the team and approach to ensure delivery on schedule. Consequently, the project accommodated multiple new challenges and demands without impact to the client’s schedule milestones. Geosyntec successfully mitigated project risks by proactively identifying threats, adjusting plans, and developing alternative approaches to maintain project resilience.