San Lorenzo Creek (Zone 2 Line B) Emergency Bank Repair Behind 1976 Wingate Way, Hayward, Alameda County
During the 2023 winter storms, the Alameda County Flood Control and Water Conservation District (District) was informed of a sudden and unexpected major scour and erosion along the south bank due to high and fast flow in San Lorenzo Creek behind the private property of 1976 Wingate Way. The portion of existing bank behind 1960 and 1980 Wingate Way also experienced severe bank erosion. The bank scour undermined the soldier pile retaining wall located along private property line on District property and exposed some of the concrete pile wall foundation creating a high risk of wall instability. The District proposes an emergency stabilization of the scoured south bank along the backyards between 1960 and 1980 by: removing fallen trees that are obstructing and redirecting channel flow towards the creek embankment where existing retaining wall is located, installing rock slope protection (RSP) mixture in the large scoured hole and along the south bank and in front of the wall, and backfilling behind the soldier pile retaining wall to reestablish the original grade of the private backyards. RSP mixture will consist of equal parts: ¼ Ton Class V/VI, Class III, Class I, and 3/4 x 1/2. A total of approximately 850 cubic yards of RSP mixture will be placed within the scoured bank and in front of the retaining wall, an approximately 3,500-square-foot area. Backfill materials behind the retaining wall will consist of layers of: RSP mixture, universal gravel filter, Class 2 permeable material, and topsoil. The District will construct the permanent fix the following year after the temporary fix to restore the eroded bank, reestablish channel alignment to pre-storm condition, provide channel grade controls, and revegetate the restored bank. The purpose of this project is to alleviate the emergency of clearing the obstructions to the channel flow and stabilizing the severely scoured south channel bank.