The Metropolitan Water District of Southern California board authorized the final design to replace the fish screens on the inlet/outlet tower at Diamond Valley Lake.
The MWD board’s February 11 action also appropriated $380,000 for the work while finding the project categorically exempt from California Environmental Quality Act review.
Diamond Valley Lake has a maximum storage capacity of 810,000 acre-feet and provides emergency storage in the event of a major earthquake, carryover storage in periods of drought, and seasonal storage to meet member agency demands. The inlet/outlet tower east of the lake’s Owen Dam is 266 feet high; nine tiers of twin ports spaced 25 feet apart allow water to enter or exit from different lake elevations.
A hydraulically-operated butterfly valve controls flow through each port, which is seven feet in diameter. The ports open into a wet well which rises the full height of the tower above the pressure tunnel at its base. The lake water passing through the tower into the pressure tunnel can be diverted either to the Wadsworth pumping plant or to the adjacent pressure control
When water is being withdrawn from the lake, fish screens are placed in front of the ports to prevent debris from entering the tower. In addition to protecting the fish, the screens also protect the valves at the tower and at the pressure control structure and the pump turbines at the Wadsworth pumping plant. The four fish screens are each 26 feet wide by 19 feet tall. The fish screens are raised and lowered to the desired elevation by a pulley system operated by a gantry crane mounted on top of the tower.
The fish screens, like other parts of Diamond Valley Lake, are inspected periodically. An inspection of the fish screens identified extensive corrosion damage in the coated carbon steel structure elements including the hoist beam eye bars, the support beams, and the retaining pins. The corrosion was likely caused by galvanic action between the screens’ stainless steel and carbon steel components.
In November 2012 the MWD board authorized the preliminary design phase to replace the fish screens with units which would not be susceptible to galvanic corrosion. The preliminary design phase is now complete. The final design activities include engineering design, preparation of drawings and specifications, receipt of competitive bids, and refinement of estimated construction costs. The actual project will replace the fish screens using stainless steel components while refurbishing corroded lifting blocks, screen supports, and other structural elements.
The total construction cost is estimated at between $1.7 million and $1.9 million. MWD staff will return to the board with a request to award a construction contract after the final design is completed. The $380,000 for the final design covers $256,000 to prepare drawings and specifications, $72,000 for project management and receipt of bids, and $52,000 for contingency. MWD staff will perform all final design work.