A new kind of Delta diversion could extract water at a slow enough rate, and across a wide enough area, that proponents say fish would hardly notice it.
by Alastair Bland
In California’s arid San Joaquin Valley, communities have long grappled with an unrelenting challenge: Their sun-blasted region doesn’t have nearly enough water—at least not to support agriculture of the scale and intensity that has been established in its fertile soils. Though water is imported from as far away as the Klamath River basin via massive conveyance facilities, supplies have been spread thin by nut orchards that now span the valley floor. Groundwater reserves are declining, and worsening droughts and warming winters aren’t helping. Neither are water pumping restrictions meant to protect imperiled fish species in the Sacramento-San Joaquin Delta.
But what if there was a way to not just maintain current Delta water exports but increase them without impacting the San Francisco Estuary’s remaining fish? Water supply advocates in the region say they have a plan for one. They call the proposed system “fish-friendly diversions.”
Still gestating in early planning stages and with no official endorsement from government, the idea is to place perforated pipes buried in gravel at the bottom of a placid Delta slough. Drawn by gravity alone, water would enter this so-called “infiltration gallery,” percolate into the pipe system, and flow southward on a slight downward tilt. Within a few hundred yards, it would connect to a pumping station that would lift the water and send it to existing surface conveyance arteries, like the California Aqueduct and the Delta-Mendota Canal, and to groundwater storage basins.
While pumps would play an essential role in the system—also billed “environmentally-friendly diversions”—the absence of any suction force at the intake means the facility could extract water at a slow enough rate, and across a wide enough area,that fish would hardly notice it. More importantly, they would not be drawn off their migration routes or into remote backwaters thick with predatory fish—a major environmental problem associated with the state and federal water projects.
“We should be able to divert water from rivers without harming their ecosystems,” said Scott Hamilton, the technical committee chairman for the Water Blueprint for the San Joaquin Valley, the water solutions collaborative pushing the project. “We haven’t done a very good job of that, which is evidenced by our declining fish populations.”
Hamilton said installing the infiltration gallery and connecting it to nearby infrastructure could cost as little as $2 to $3 billion—about a tenth the cost of the proposed Delta tunnel. By producing an annual yield as high as 1.7 million acre-feet of water, the system could increase Delta exports by more than a third, he said. The system would only operate in wet years, remaining idle in years of low flows—part of the theme of minimizing environmental impacts. Construction could be simplified and its impacts reduced by designating an uninhabited Delta island for the project: The pipes could be laid and buried under gravel while the land is dry. Once ready, breaching a nearby levee could inundate the site and initiate operation.
The idea is much more than a pipe dream. Infiltration galleries have been built around the world, and they are considered an effective way of naturally filtering water for human uses and withdrawing it from rivers minus more complex diversion infrastructure. In California, such systems have been installed under the beds of the Russian, Eel, Santa Ana, and other rivers. The Turlock Irrigation District laid an infiltration gallery under the Tuolumne River in 2001. After a lengthy process of constructing connecting pumps and pipes, the system—part of the Regional Surface Water Supply Project—went online last year and has been withdrawing about 15 million gallons, or 46 acre-feet, of water daily. The water is diverted into the municipal supply system for the towns of Ceres and Turlock, according to Josh Weimer, the Turlock Irrigation District’s external affairs department manager.
Weimer explained that the system was strategically placed downstream of more than 20 miles of prime salmon spawning habitat.
“The ability to keep more water in that section and then pull it out lower in the river becomes a beneficial use of the water,” he said.
The U.S. National Marine Fisheries Service even has guidelines for building and maintaining infiltration galleries in rivers that support salmon and steelhead—species that can easily be impacted by riverbed disturbances.
Scientists, however, aren’t all sold on the notion of fish-friendly diversions—at least not in the Delta. Some say that a major infiltration gallery in this already ailing estuary will worsen environmental impacts related to water exports.
“[Fish-friendly diversions] are still taking water from critical habitat, even if they are not entraining fish,” said Jeffrey Mount, a senior fellow at the Public Policy Institute of California who has studied California’s hydrology and waterways for decades.
Shrinking Supply Ahead
Fortifying California’s water supply infrastructure is a top priority of state leaders, especially in a time of rapidly changing climate. In a recent report, the California Department of Water Resources estimated that the conveyance capacity of the State Water Project—the system of reservoirs and canals that supplies 27 million people and 750,000 acres of farmland with water—could decline by 23% in the next 20 years due to climate change effects.
Hoping to mitigate such impacts, officials are advancing major projects to increase storage and diversion capacity. The Delta tunnel would draw water from the northern end of the estuary in wet years and carry it under the fragile ecosystem, eventually delivering flows to the State Water Project’s California Aqueduct—a lifeline for the San Joaquin Valley and southern California. Sites Reservoir, approved for construction in the western Sacramento Valley, would similarly be filled with water in years of high flows. However, these projects are controversial, with opponents again warning that, by diverting more water from the ecosystem, they will push imperiled species like Chinook salmon and white sturgeon closer to extinction.
Also, the new projects are certain to come with crushing price tags. The tunnel, for instance, is likely to cost at least $20 billion while exporting an average of 500,000 to 1 million acre-feet of water from the estuary each year—relatively low returns for such a huge investment. While building costly water systems for wealthy cities can make financial sense, doing so for farms—which typically need abundant water at a low cost—does not.
“The problem with the tunnel is that it’s too expensive for agriculture,” Hamilton said.
The fish-friendly diversions system could be much more cost-effective. Moreover, as planned it would be remarkably gentle with the water it handles, extracting it from the bottom of the estuary at a percolation pace of just one inch per minute. That’s the maximum rate that Hamilton says has been shown to have essentially no impact on Delta smelt larvae—the most sensitive life stage of the most sensitive species in the waterway.
Past the Point of Fish-Friendly Diversions?
The idea that more water can be harmlessly diverted from the Delta may be a tough sell when exports are already, according to many experts, unsustainably high. The state and federal pumping projects near Tracy pull between 3 and 5 million acre-feet annually from the estuary. This can cause saltwater intrusion, elevated water temperatures, and algal blooms. It has also contributed to the collapse of salmon, smelt, and sturgeon populations. While many farmers and water supply managers decry fresh water that reaches the ocean as a resource wasted, biologists say this is a crucial ecological function of an estuary’s water. They warn that even the most passive of water diversions will exacerbate the ecological impacts of reduced flows.
Jon Rosenfield, the science director at San Francisco Baykeeper, said the fish-friendly diversion system, by focusing on avoiding impinging fish at the intakes, fails to address what he considers a greater issue.
“[Entrainment] is not the largest problem with proposed new diversions,” he said. “Removal of more water from our rivers and Delta is the largest problem.”
Peter Gleick, co-founder of the Pacific Institute—an Oakland thinktank focused on sustainable water supply and growth—questions how much more water can be squeezed from the Central Valley’s watersheds. Increasing Delta exports, he said, has proven in modeling scenarios to be the least viable solution to San Joaquin Valley water woes, whereas using less water in the first place, treating and reusing wastewater, and capturing stormwater have penciled out as better options.
“Our assessments show these approaches are cheaper, faster, and more environmentally appropriate,” said Gleick, the author of The Three Ages of Water: Prehistoric Past, Imperiled Present, and a Hope for the Future.
A 2022 analysis of the fish-friendly diversions, written by Hamilton and posted to the website of the Water Blueprint for the San Joaquin Valley, argued otherwise.
“There is no amount of conservation, recycling, and desalination that can feasibly solve [California’s water crisis],” the report stated.
The Water Blueprint’s website cites “increased dependence on foreign-produced food” as one problem that could be solved by capturing more water from the Delta. To the extent that food security is a legitimate concern in California, curbing exports of farm goods, and retaining food in the region it was grown, could also alleviate the problem. In 2022, when California farmers reaped $55.9 billion in sales, $23.6 billion worth of those goods went to eastern Asia, Canada, the European Union, and other regions.
Gleick said fallowing farmland—in other words, producing less food—will be a key step toward achieving water sustainability in the San Joaquin Valley. In fact, this outcome is all but certain to ensue as new groundwater extraction rules, mandated by the 2014 Sustainable Groundwater Management Act, take full effect in the next several decades. By some estimates, a half-million acres of irrigated cropland could be idled and converted to parks, wildlife refuges, and solar energy arrays.
Hamilton said fish-friendly diversions could, at best, partially offset these impacts to farming. Because the proposed Delta infiltration gallery would only operate at full capacity during wet periods–when supply systems everywhere tend to be flush with water—its usefulness, he explained, may be limited without coordinated upgrades to other water infrastructure.
“Demands are not that high in wet years, so success of the project depends on long-term storage of water,” he said. Enhanced groundwater recharge systems, he added, would ideally receive most of the new diversions.
Still, even if groundwater basins are filled up, there may be no way around the perennial problem that the San Joaquin Valley is overplanted. Hamilton said that installing fish-friendly diversions will be “better than doing nothing but not enough to solve the problem.” That is, fallowing land is probably inevitable.
“Even with this increase, there is not enough water to prevent hundreds of thousands of acres of irrigated agriculture going out of production in the San Joaquin Valley,” he said.
This article was produced by Estuary News Group and funded by the Delta Stewardship Council.
