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Army Corps' 10% Stone Lock design aims for 200-year flood protection; $21 million estimate
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Summary
Army Corps contractor presented a draft 10% design for Stone Lock that would add a reinforced concrete closure, fish passage, and deep foundations; estimated cost $21 million, with geotechnical borings and schedule constraints ahead.
The Army Corps’ draft 10% design for a permanent closure at Stone Lock would add a reinforced concrete closure structure just west of the eastern sector gates, provide 200-year flood protection for the adjacent reach and include fish-passage features, a pedestrian/maintenance bridge function, and levee tie-ins, presenters told the West Sacramento Area Flood Control Agency on Feb. 19.
Andrew, the contractor presenter, said the existing Stone Lock — built in 1961 and decommissioned in 2000 — is “leaky” and no longer provides 200-year protection. The draft design would roll in the sector gates, remove stop logs, and install a reinforced concrete barrier that also carries pedestrian and emergency vehicle access. The design as presented includes four 48-inch pipes to allow fish passage and freshwater flow that can be closed during high flood events.
Staff and the Army Corps contractor flagged important geotechnical constraints: shallow soils are poor because of a gravel and dense sand layer under the structure. The geotechnical consultant proposed a deep foundation design — roughly 72 drilled piles approximately 100 feet deep filled with concrete — to support the concrete closure. The presenter said the design team is also evaluating alternatives, such as jet grouting, to reduce the number of piles and potential cost escalation. "We do see a possible cost escalation due to that deep foundation," the presenter said.
Cost and schedule were emphasized as constraints. The 10% design carried an estimated cost of $21,000,000 (including contingency). The presenter described the 10% design as due for completion around March, with 30% design initiation expected in July; Army Corps contracting mechanisms and staffing could slow progress. Next technical steps include borings inside the lock — a novel and technically challenging task that may require crane-in barges or sector-gate operations — and further coordination with the Port of West Sacramento and regulatory partners.
Board members raised hydraulic and construction concerns. In response to a question about water-surface elevations, the presenter referenced a Corps hydraulic report indicating a roughly 200-year-event elevation of about 20 feet for the Deepwater Ship Channel and about 34 feet on the Sacramento side, producing a significant head differential for design. When asked about pile installation vibrations, the presenter said piles would “most likely [be] drilled and then filled with concrete,” not impact-driven piles, to reduce neighborhood disruption. The presenter also noted Stone Lock has historic designation considerations and staff will try to avoid altering the structure where possible.
The board was told the 30% design is expected to start in summer and that borings and geotechnical review will continue; staff will also coordinate with the Port and design partners to reduce construction impacts.
