Rising sea levels, as well as droughts and earthquakes, threaten the levees protecting the Sacramento-San Joaquin river delta, which supplies 25 million Californians with fresh water. But the state’s solution isn’t to build higher but lower—150 ft below the earth.
California’s Dept. of Water Resources plans to dig two gravity-fed, 40-ft-dia tunnels under the delta to move fresh water from the Sacramento River to federal pumping stations in the southern delta. First proposed in the 1960s as a peripheral canal skirting the delta, the $15.7-billion delta tunnel project received an environmental certification from the state in late July.
“We’re engineering for a 200-year storm event in the delta, plus another 18 inches for sea-level rise,” says John Andrew, DWR’s assistant deputy director. “We’re figuring 55 inches in sea-level rise at the Golden Gate in the next 100 years.” With that amount of sea-level rise, saltwater would be pushed into the delta.
To avoid saltwater intrusion and reduce reliance on the delta’s 1,100-mile levee system, the proposed California WaterFix project would draw water from the Sacramento River in the north of the delta. The system could divert up to 9,000 cu ft of water per second into about 43 miles of tunnels to a new pumping plant on the delta’s southern edge.