The Searsville Dam stores and delivers water for Stanford University facility operations, habitat, and ecological research. The dam is in sound structural condition, but it prevents fish passage to four creeks and has been trapping sediment above the reservoir. If the dam is not removed or modified to allow water flow, the watershed upstream will become filled with sediment. To restore the natural sediment process and maintain Searsville’s water supply function, McMillen has designed and is constructing a tunnel at the base of the dam that is fitted with a roller gate to control the flow of water and sediment.
Prior to flushing 1 million cubic yards of sediment downstream, our team will develop a pilot channel. This channel will help enable the preferred natural erosion process whereby sediment will be moved downstream over 4-8 years. If the natural erosion process does not flush all the sediment needed, mechanized sediment movement may be required. This would likely require excavating material from the channel overbank areas and moving it closer to the dam, where it can be released through the tunnel during a larger flow event. We will implement an adaptive management process for this portion of work to allow the sediment evacuation processes and final channel restoration to adjust to actual conditions.
Following the release of sediment, the delta will be graded, and the final channel alignment will be constructed and stabilized. Our team will then re-establish the natural creek to restore volitional fish passage via a roughened channel/boulder cascade fishway. This fishway will provide upstream and downstream fish passage, hydraulic complexity, resting pools, and other refugia.
Because our core project goals center around restoring natural environments, our approach will minimize impacts during construction and focus on the safety of the existing aquatic habitat downstream of the dam. We will avoid increasing flood impacts downstream with the installation of sediment-trapping features, and any new structures are required to work with existing and natural channel morphology. It is crucial to maintain a healthy habitat as we work to reinvigorate the landscape and provide a viable habitat for local plants and wildlife.
We are responsible for the following work:
• Alternative analysis and value engineering
• Lifecycle cost analysis and risk assessment
• Construction planning, including cost estimates, schedules, staging, and logistics
• Environmental and permitting support
• Dam stability, structural, and seismic evaluations and modeling
• Refinement to existing hydraulic, hydrologic, sediment transport, and scour analysis and modeling
• Geotechnical investigations including rock coring
• Electrical components including distribution and controls
• Civil work including new access roads, plunge pool modifications, and erosion and sediment control
• Revegetation including planting and seeding
• Assistance with community and stakeholder coordination
