State water officials have asked local groundwater agencies to better prevent land subsidence. Simultaneously, the state is also working to fix the damage caused by sinking land.
Subsidence is caused by the over-pumping of groundwater. It occurs in many parts of California but is especially pronounced in the San Joaquin Valley during drought years. When snowpack is below average and allocations of water stored in reservoirs are low, significant water users like the agricultural industry turn to underground aquifers for their water supply. According to the U.S. Geological Survey, portions of the Valley sank 20 to 30 feet in the 40 years after researchers began observing subsidence in the 1920s, and a NASA analysis of satellite imagery during the last drought found thatsome areas of the Valley sank as many as 22 inches during a period of just 16 months.
The sinking of land is slowly impairing the complex system of canals that deliver water throughout the state. According to a 2017 report by the Department of Water Resources (DWR), the sinking and buckling of portions of the California Aqueduct, which runs 444 miles from the Sacramento-San Joaquin Delta to the Tehachapi Mountains,has reduced its flow capacity and its ability to store water in overflow pools.
That’s a concern to Roger Bales, an engineering professor with the University of California, Merced. “These aqueducts can still move water to users in the San Joaquin Valley or Southern California, but they can’t move as much water during wet years as was their design capacity,” he said, which also endangers water storage projects that act as an alternative to pumping groundwater. “If we can’t store this wet-year water, then we can’t pump groundwater sustainably.”
Two years ago, entities throughout the state known as groundwater sustainability agencies were tasked with submitting plans to the state that detail how they plan to eliminate groundwater over-pumping by 2042 as required by the Sustainable Groundwater Management Act. But in recent months, as DWR officials have returned their comments on those documents, they’ve told many water agencies that their plans won’t be approved unless they better demonstrate how they’ll prevent future subsidence.
For example,in a comment letter sent in response to the plan submitted by a sustainability agency covering much of Merced County, DWR wrote that “staff do not believe that the [groundwater sustainability plan], in a Subbasin with significant historical subsidence and with infrastructure identified as being susceptible to future subsidence, should be recommended for approval without identifying the total cumulative amount of subsidence that can occur without causing significant and unreasonable impacts to beneficial uses and users, surface land uses, and property interests. “
So far, of the 40 sustainability plans that DWR has reviewed in the Central Valley, Central Coast and Northern California,it’s approved only four of them. The agency also demanded more actionto protect drinking water supply and quality should groundwater levels continue to fall.
Sustainability agencies have until January 31 of next year to submit revised versions of their plans for final approval, and those that fail at that time will be required to revise again within 180 days or risk being taken over by state water officials.
Meanwhile, DWR recently initiated$100 million dollars’ worth of repairs to the state’s ailing water infrastructure, particularly to the California Aqueduct, San Luis Canal, Delta-Mendota Canal and Friant-Kern Canal. Together, those canals deliver water to more than 29 million people, 2.9 million acres of farmland, and 130,000 acres of wetlands.
The funding comes from this year’s state budget and another $100 million has been authorized for next year. The repairs will also receive some cost sharing from the federal government and local cities and counties.
Roger Bales agrees that $100 million is an important investment in California’s water infrastructure, but says that these complicated systems have far more needs, stemming from more problems than subsidence. Among other things, “we need to pay attention and do some major maintenance on our headwaters. There’s changes that need to occur around some of the dams for storage, because some of the spillways don’t have capacity to move these high flows that occur during the intense rainstorms that we’re getting and are expected to continue to get in a warming climate,” he said. “So there’s a whole range of infrastructure needs that could easily add up to a billion dollars.”
Many of these projects could receive a boost from the recently passed Bipartisan Infrastructure Deal, which sets aside nearly $10 billion for water infrastructure projects around the country.
