A controversial plan to build a 45-mile-long tunnel to divert water from northern California to the arid south has revived with release of a draft environmental impact report by the California Dept. of Water Resources (DWR).

The 3,000-page analysis outlines multiple alternatives for the proposed Delta Conveyance Project. If built, it would take water from the Sacramento River and move it beneath the Sacramento-San Joaquin River Delta to reach the state’s main north-south water supply network. Optimistic scenarios estimate construction getting underway no earlier than 2028 and taking a decade to complete.

“Two out of three Californians rely on the State Water Project for all or part of their water supply,” said DWR Director Karla Nemeth in a statement. “Modernizing this infrastructure is essential to adapting to a future that includes more frequent extremes of drought and flood, and greater water instability.”

The current project was launched in 2019 by state Gov. Gavin Newsom when he scrapped a previous plan featuring a twin-tunnel solution for one with a single tunnel. The effort is aimed at balancing the state’s water supply resources with ever-growing demand amid multiple climate-related uncertainties. Conservation groups have opposed the pipeline due to the possible environmental impacts it would entail.

A 2020 estimate puts the cost of a single-tunnel system at $16 billion, although the projected costs of the current plan are not in the report. State-issued bonds for what is expected to be at least a ten-year-long construction effort would be funded by the non-profit State Water Contractors, a 27-member association of local public water agencies that purchase water from the DWR’s 700-mile water storage and delivery system that supplies water to 27 million California residents. 

Jennifer Pierre, SWC’s general manager, said in a statement that the draft report, “clearly shows that the project has been downsized, refined and redesigned to avoid and reduce local impacts and address environmental concerns.” Pierre also called the Delta Conveyance Project “the right project at the right time” to modernize the state’s existing water supply infrastructure. 

The current plan calls for building a pipeline capable of conveying up to 6,000 cu ft per second (cfs) of water drawn from the norther reaches of the Sacramento River’s delta 45 miles downstream to connect with a new pumping station/aqueduct complex. The water would be deposited into the Bethany Reservoir, which connects to the California Aqueduct.

The draft report, which examines eight alignment alternatives, notes that the Bethany alignment “would provide the same climate resilience, seismic resilience, and water supply reliability as the other 6,000 cfs alternatives,” but with fewer or substantially reduced environmental impacts.

Not everyone agrees. Originally conceived as part of the state water system in the 1960s, the concept of a water supply bypass around the Sacramento River delta has been criticized for its cost, construction impacts and long-term environmental consequences, particularly ecological effects of reduced freshwater flows through the estuary. 

Information released by DWR as part of the draft report acknowledges that such changes to the delta “have the potential” to affect migration and spawning habitat of several salmon species. Up to 3,500 acres of wetlands would be restored to offset the environmental damage.

The acceleration of climate change has added another dimension to the debate. DWR claims the Delta Conveyance Project will help California water system users capitalize on the increasing frequency of major storms and other extreme weather events. Had the project been operational during the big storms in October and December of 2021, the agency claims it could have captured and moved about 236,000 acre-feet of water, enough to supply 2.5 million people for a year.

Opponents counter that a more likely scenario are protracted droughts, such as the current three-year-old dry spell that has drastically curbed state water allocations.

“Climate change continues to impact the state’s hydrology, and there is no certainty as to the amount of water that will be available for the project when it’s completed,” Sierra Club California Director Brandon Dawson said in a statement. Instead, he asserts that the state would be better served by focusing on sustainable water management efforts—conservation, efficiency, recycling and stormwater capture—that are environmentally beneficial and a better option for building regional resilience.

Another criticism is the potential effect that larger water diversions from the Sacramento River Delta will have on its existing agricultural customers.

Although DWR insists that the Delta Conveyance Project is not proposing to increase the total quantity of water permitted for diversion under its existing water rights, three Sacramento-area congressional representatives recently introduced legislation that would prevent the U.S. Army Corps of Engineers from issuing a Clean Water Act permit for the project.