ENGEO stabilized about 5,000 feet of the Alamo Creek’s Main Branch. Our hydraulic design, construction plan and specification preparation, and testing and observation served to reverse the watershed’s hydromodification created by poorly mitigated urban development runoff upstream of the repair area. The increased flow rates and durations in the creek caused severe downcutting and slope stabilization issues in the repair reach. In addition, two culvert crossings had been historically installed in a manner that unnaturally concentrated stream flows and created localized expansion and contraction scour damage. We replaced the culvert crossings with a single free-span vehicular bridge.
Our scope of services for the project included performing HEC-RAS hydraulic flow modeling of the creek, evaluating creek bed and bank erosion potential, and preparing improvement and mitigation plans for the creek, which were approved by the Regional Water Quality Control Board (RWQCB), the Army Corps of Engineers, the California Department of Fish and Game, and the Contra Costa County Public Works Department. The scope also analyzed hydrologic and hydraulic conditions of the existing and proposed creek, geotechnical parameters for post-project slope stability, and biological considerations. Under separate contract agreements, ENGEO provided geotechnical recommendations for the vehicular bridge, observed the associated abutment driven piles, and provided special inspection services for steel and concrete placement.
ENGEO observed construction and testing services for the project, which included tracking contractor progress during construction and monitoring the placement of engineered fill and rock structures that construction placed in the reconstructed channel. Construction was substantially complete in November 2005. We now monitor the stabilized area and provide annual hydrologic function reports to the project owner, as required by the project permit.