The Crystal Springs Reservoir water storage and conveyance systems required seismic upgrades to all its infrastructure including dam, shorelines, low level outlets, tunnels, and intake towers and audits. Ballard provided diving, remote inspection, and marine construction support to perform heavy underwater construction. This involved cast-in-place underwater concrete, underwater pipe installation, grouting, and installation of structural steel and fish screens.
Scope of Work
Utilizing Ballard’s master divers and Nitrox diving systems, this project improved seismic resistance and delivery reliability of this transmission system. The project area (including all construction, staging and access areas) covers approximately 135 acres and is composed of seven distinct project components, running approximately seven point six miles across the Peninsula Watershed. Remotely Operated Underwater Vehicle (ROV) inspection operations, using video and sonar systems, were performed at the southern end of the Lower Crystal Springs Reservoir at the Upper Crystal Springs Dam.
Utilizing the ROV allowed Ballard’s operators to provide detailed mapping of the forty-two-inch pipe and made it possible to capture the aggregate formwork marks from previous repairs. Even though the culvert had a “dogleg” in the path of travel, the ROV was able to document anomalies found in the pipe, conditions of the internal ring structure, and the presence of new damage.
Ballard was tasked with the underwater lining of a brick-lined tunnel called the “lower culvert.” When performing initial diver inspection of the “lower culvert,” crown failures (bricks from the crown laying in the invert of the tunnel) were discovered eighty feet underwater on a main water conveyance tunnel connecting Crystal Springs’ and San Andreas’ Reservoirs. The diving inspection was suspended, and Ballard mobilized an inspection class ROV to perform the inspection safely with the use of robotics, video, and sonar. The ROV found multiple crown failures that prevented the divers from accessing the pipe to install the new grouted HDPE liner.
To resolve the issue, Ballard designed a modified horseshoe support rib, installed by divers, to accommodate the installation and grouting of the liner pipe in all failure locations. Starting at the opening, divers worked their way into the tunnel hundreds of feet, installing dozens of supports to ensure diver safety throughout construction. After installation, continued improvements to the reliability of the system were performed, leaving the water storage and conveyance systems in a much more updated state.
Location: San Mateo, CA
Diver Depth: 120ft