COWI has been selected by the Santa Clara Valley Water District (Valley Water) to provide construction management services for the Anderson Dam Tunnel Project (ADTP). The tunnel is part of Valley Water’s plan to drain the reservoir in preparation for the Anderson Dam Seismic Retrofit Project, which will strengthen the dam to safely withstand a strong earthquake.
The new low-level outlet system will allow Valley Water to reliably and quickly drawdown the reservoir, providing a greater ability to maintain water levels. The tunnel will later be used by the larger seismic retrofit project to facilitate full reservoir drawdown. The outlet system will then be converted into a larger diversion system to bypass flows during removal and reconstruction of the existing dam.
The project consists of construction of a new outlet system including: a 1,700-ft long underground tunnel up to 25 ft in diameter, 8-ft-diameter lake tap, outlet structure, discharge channel, and reopening of the original Coyote Creek channel (northern channel) downstream of the existing dam, reservoir rim and bank stability improvements, and existing intake stabilization improvements. Work will also include concrete weirs, road work, utility relocation, traffic controls/detours, revegetation, and community outreach coordination.
As Construction Manager, COWI will administer the construction contract and provide unified oversight of the project during construction on behalf of Valley Water. After the tunnel is finished, Valley Water plans to begin construction on the new dam in 2024 and finish by 2030.