SAN LORENZO CREEK (ZONE 2, LINE B) CONCRETE CHANNEL REPAIR DOWNSTREAM OF WASHINGTON AVENUE, IN SAN LEANDRO AND SAN LORENZO.

The Alameda County Flood Control and Water Conservation District {District} owns and maintains San Lorenzo Creek between San Francisco Bay and Foothill Blvd. in San Leandro, San Lorenzo and Hayward, that was constructed by the U.S. Army Corps of Engineers (Corps). On 12/29/2024, the concrete portion of San Lorenzo Creek just downstream of Washington Avenue suffered severe damage and distress due to the high pressure 6" PG&E gas line and 12" EBMUD water line leaks. These leaks caused uplift of the channel invert and longitudinal cracking, leading to piping erosion of soil beneath the concrete channel and behind the concrete channel walls, creating voids and a sinkhole. The concrete channel invert serves as the footing for the channel retaining walls and its continuing functionality and serviceability are crucial for flood control. The District completed preliminary site evaluations and proposes to perform temporary stabilization measures in summer 2025 including low-strength grout injection through the concrete channel invert to fill voids below, sealing and filling of the cracks in the concrete channel slab, installing temporary steel bracing system just above the top of channel walls, or sheet piles/cast-in-drilled piles behind the channel walls with tie rods to the walls. Permanent reconstruction of about 350' of the damaged portion of the channel would require full construction window in summer 2026 between mid-April and mid-October. Both temporary and permanent work will require placement of temporary cofferdams upstream and downstream of the proposed work to bypass nuisance flow in the channel during the dry season. Since PG&E and EBMUD lines also cross under the concrete lined channel, it is likely that the investigative work, repairs and/or replacements of these utility lines may occur the same time as channel reconstruction of the concrete channel. The project limits are about 350' from Washington Avenue crossing going downstream in San Lorenzo and San Leandro. Once the project is completed, the cofferdams will be removed, and the natural flow of the creek will be restored. The primary goal of the project is to temporarily stabilize the failed concrete line channel bottom and walls first in summer 2025, and then reconstruct the concrete lined channel in summer 2026 to the original U.S. Army Corps of Engineer's design, with incorporation of current design criteria, and restore flood control protection for the surrounding community.