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Sweetwater Authority committee authorizes seismic study update for outlet tower
Summary
The Engineering & Operations Committee authorized the general manager to execute a contract with WSP USA Inc. to update the seismic evaluation of the Sweetwater Dam outlet tower and conduit for up to $286,378, moving a 2003 analysis toward potential design and cost estimates.
The Sweetwater Authority Engineering and Operations Committee on Feb. 5 authorized the general manager to execute a contract with WSP USA Inc. to update the seismic evaluation of the Sweetwater Dam outlet tower and its conduit for a not-to-exceed amount of $286,378.
The update will refresh a 2003 seismic assessment and, if authorized by the full board, could include preliminary design considerations and cost estimates to inform any future rehabilitation decisions. The committee voted unanimously to recommend the contract to the board; Directors Castaneda, Cox and Martinez voted in favor.
Staff explained the outlet tower was built with the original dam work in 1888 and later raised about 20 feet; portions of the original masonry remain. The 2003 study, performed by GEI, concluded a roughly 144-year return-period earthquake could cause significant cracking and possible failure but did not provide subsequent design or cost recommendations. The requested update will apply current seismic parameters and modeling approaches used in recent dam evaluations.
According to staff, the outlet tower sits about 40 feet from the dam and is not regulated by the California Division of Safety of Dams because it is not used for emergency withdrawals. The scope requested in the RFP included not only an updated hazard analysis but also potential conceptual design options and order‑of‑magnitude cost estimates so the board could evaluate budget and project priorities.
Staff said the authority received two proposals; WSP was the lower-cost proposer and scored higher on relevant dam and hydraulic-structure experience. The fiscal year 2025 operating budget includes a line for the study; staff noted the budget allocation for this task is $300,000 and WSP’s proposal is within that amount.
Committee members asked whether the update would require divers or underwater inspection; staff responded the work will be primarily model- and data-driven using previously collected physical testing and updated seismic parameters rather than routine underwater dives. Members also discussed whether a potential future rehabilitation could be coordinated with planned dredging work at the reservoir and noted that any construction would move the item from operating expense to capital project status. Staff said further design and construction decisions would follow only if the study indicates a project is warranted.
The committee recommendation moves the contract authorization to the full board for final approval and execution.
