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Eastside Reservoir – West Dam P-1 Inlet/Outlet Tunnel

Eastside Reservoir – West Dam P-1 Inlet/Outlet Tunnel

Hemet, California
Metropolitan Water District of Southern California
Contract Value
$13 Million
Completion Date
Market Sector
Dam & Hydro

Southern California’s experience with long drought periods—coupled with the lack of sufficient surface storage capacity—led to the Metropolitan Water District of Southern California’s (MWD) allocation of more than $2 billion to construct the 4,500-acre Diamond Valley Reservoir, now known as Diamond Valley Lake.

The Lake, which doubled Southern California’s surface water storage capacity to more than 800,000 acre-feet, can store up to a six-month emergency water supply and provides supplemental water during droughts and peak summer usage.

Atkinson, in a joint venture with Zachry Construction Corporation and Washington Group, constructed the massive 1.7-mile long, 300-foot high Eastside Dam. We also constructed related infrastructure such as the Eastside Reservoir inlet/outlet tower and pressure tunnel.

The project team excavated 5.5 million cubic yards of earth for the Eastside Dam inlet/outlet approach channel, more than 6 million cubic yards of earth for the dam foundation, and 70 million cubic yards of rock for the dam embankment.

The 270-foot inlet/outlet tower—which includes an access bridge—required 95,000 cubic yards of concrete and nine million pounds of reinforcing steel. The mechanical package included an emergency gate and valves, along with 40,000 feet of miscellaneous piping. The electrical scope incorporated multiple raceways, instrumentation, and communications ducts.

To connect the tower to the pumping station located near the downstream face of the existing West Dam, the team constructed a 2,300 foot-long, 24-foot diameter horseshoe-shaped pressure tunnel by drill and shoot excavation, placing 20,000 cubic yards of concrete behind a steel lining.