Modification of Existing Culvert Outfall along Line B downstream of Harrison Street in the City of Oakland, Alameda County, California, Zone No. 12 Project

The Alameda County Flood Control and Water Conservation District is planning to modify the existing underground reinforced concrete culvert outfall along Line B downstream of Harrison Street in Oakland to address insufficient capacity during a 100-year design storm event. The project involves installing a new 50-foot-long, 6-foot by 6-foot reinforced concrete culvert box beneath the sidewalk adjacent to the current structure, which will be integrated into the existing outfall system. To accommodate this addition, approximately 14 linear feet and 10 cubic yards of the western concrete channel wall will be removed, and a warped concrete wing wall will be installed to match the existing channel alignment. Additionally, about 128 square feet of the existing concrete apron will be demolished and rebuilt to properly connect the new structure. The modification will enhance stormwater conveyance capacity at the outfall, ensuring compliance with required engineering standards for extreme rainfall events. This project is part of the broader Zone 12 Drainage Master Plan and is intended to future-proof the drainage infrastructure in preparation for additional underground culvert expansion under Harrison Street and 27th Street.