The benefits of a long-sought and controversial project to replumb the Delta and send more water south are speculative at best, argue elected leaders from Yolo and Sacramento counties.
The California Department of Water Resources is using the winter storms to claim that the proposed Delta Conveyance project would help ensure a more reliable water supply for the State Water Project in light of how climate change will alter seasonal patterns of rain and drought.
In reality, the benefits of the conveyance project are speculative.
The Delta Counties Coalition demonstrated for over 15 years that resources slated for the tunnel would be better spent on sustainable, resilient water infrastructure around the state (such as groundwater recharge, storage, recycled water expansion, desalination) instead of further increasing reliance on Sacramento River freshwater flows, which is in direct conflict with a Delta Reform Act requirement to reduce reliance on the Delta.
DWR proposes that water districts reliant on the Delta for a portion of their water supplies invest more than $16 billion to sporadically convey water from large storms. Tunnel proponents claim that when California experiences large precipitation events, the tunnel could capture and move much of that water to other areas.
This is only true if we ignore the assumptions being made.
First, there is an assumption that large rainstorms would occur frequently enough to make the construction and maintenance costs of the tunnel worthwhile. This assumption has not been supported by any cost-benefit analysis, or the unpredictable weather patterns over the last 10 years. While the tunnel could help convey water during certain scenarios, this does not mean it can capture significant amounts of water as purported, or be a sustainable and reliable water source.
Over the past two decades, the Sacramento and San Joaquin valleys experienced very few to no large precipitation events several times. In 2016, for example, Sacramento River flows were 32% lower than average. In 2018, it was 20% below average and 66% below in 2020. The drastic precipitation swings demonstrate that the Sacramento River cannot be a reliable source of water, undermining the notion that the tunnel project would somehow increase overall water supply reliability.
Additionally, the tunnel’s operational criteria assumes that storage space would be available. However, as the Public Policy Institute of California recently noted in a policy brief, in 2011, 2017 and 2019, “the San Joaquin River was flooding, protections for salmon and steelhead were suspended, and the two water projects – Central Valley Project and State Water Project – could pump without restrictions. But the major reservoir south of the Delta – San Luis – was full, and there was simply no place to put the additional water.”
Therefore, not only would tunnel operations be virtually useless during long-term droughts, but it could have limited usefulness during wetter periods, too.
Another unfounded assumption is that the tunnel would operate exactly as assumed in the draft environmental impact report. However, the proposed operational criteria, which also would allow diversions in low flow periods, have not been given a final approval. The initial feedback from wildlife agencies, for instance, suggests that the potential impacts to anadromous fish would require modifications to the final plan. This means DWR’s examples of how much water could be captured or conveyed during any specific period can’t be relied upon yet.
Ultimately, there are far better approaches to meet the state’s water supply needs. The state should be promoting and funding projects to reduce demand, restore groundwater levels, expand water recycling and increase stormwater capture. These types of projects provide both increased water supply reliability and sustainability while avoiding the pitfalls of the Delta tunnel.