By Edward Ring, Director of Water and Energy Policy at the California Policy Center
Of all the possible ways to increase California’s water supply, nothing compares to the potential of the so-called “big gulp,” that is, the ability of new and improved water infrastructure to safely divert millions of acre feet from the Sacramento-San Joaquin Delta during high winter flows. How much water?
A study published by the Public Policy Institute of California offers an answer to this question. They measured flows through the delta over a 37 year period through 2016 and classified the volumes of water into categories including diversions for farm irrigation and municipal use, flows essential to maintain the health of the delta ecosystems, and the intriguing category “uncaptured water.” They estimated the volume of “uncaptured water” to average 11.3 million acre feet per year over the 1980-2016 period.
It’s important to avoid concluding that 100 percent of this uncaptured water could be safely diverted. And since the 2017 PPIC study came out, new regulations have increased the amount of flow that would now be classified as required for ecosystem maintenance, proportionately reducing the estimate of uncaptured water that may be available. But it is worth examining what it would take to harvest an additional five million acre feet of water from the delta each year. Successfully accomplishing this requires at least three major initiatives.
First, the delta itself has to be reengineered to remove silt. For over a century, ever since the delta was channelized, farmers and government agencies dredged the rivers and sloughs. The soil was used to enrich fields and build levees. This all came to a halt starting in the 1970s, and now the regulatory burden confronting any public or private entity hoping to dredge is prohibitive. This must change.
Dredging the delta will restore deep and cool channels to help salmon migration and increase the volume of aquatic habitat. In a channel 200 feet wide with an average depth of three feet, the proposed dredging of 100,000 cubic yards per mile would nearly double the volume of water. The benefits are tremendous.
By significantly increasing the volume of delta channels, the rate of flow during heavy runoff is increased, meaning more water can be reserved in reservoirs. As it is, Sierra reservoirs are drained during winter so they retain capacity to accommodate rapid spring runoff. To the extent rates of flow are faster through the delta, more water can be safely saved in the reservoirs.
At the same time, increasing the volume of fresh water in the delta allows the existing delta pumps to operate longer at full capacity before they reverse the current and draw in salt water from the San Pablo Bay. The combination of higher volume and faster flow in the delta thanks to dredging means more water can be withdrawn without risking salt water intrusion.
The second step necessary to take the big gulp is to increase the volume and duration of water supplying the existing delta pumps, which only have a combined maximum capacity of 30,000 acre feet per day. That means even if they ran at full throttle for 100 days, they would only withdraw 3 million acre feet. The pumps need to run at higher rates for longer periods. More diversion capacity is required.
For this reason, the “Delta Conveyance” has dominated discussions of major water infrastructure investments for the last several years. This 45-mile-long, 40-foot internal diameter tunnel connecting the Sacramento River north of the delta to the Clifton Court Forebay to the south is a controversial and expensive proposal. But at a maximum throughput capacity of 20,000 acre feet per day, and a design that permits multiple points of diversion distributed across the delta, it would go a long way toward developing sufficient capacity to take the big gulp. There are proposals to supplement the delta tunnel with other creative means to divert large volumes of water out of the delta, but expanding diversion capacity brings us to the third requirement: distribution and storage.
Will the greater volume of water in the delta post-dredging, combined with a million acre feet or more additional water reserved in Sierra Reservoirs, combined with the delta tunnel’s ability to safely remove water from several points in the delta during an extended season, enable the delta pumps to operate at full capacity for 250 days a year? Because with the existing state and federal pumps, that’s what it would take to pull an additional five million acre feet per year out of the delta.
And if we can’t run the state and federal pumps at maximum capacity for 250 days per year, then what additional projects are necessary to enable the big gulp? Should we build another forebay and aqueduct, right down the center of the San Joaquin Valley, to help move water from the delta tunnel or other diversion projects? We should consider all options; some are surprisingly cost-effective.
We also have to recognize that pouring an additional five million acre feet per year into the state and federal water project aqueducts, or even into a network that added another aqueduct to the system, would quickly overwhelm available storage downstream. One solution would be to build and expand more reservoirs. Pacheco. Los Vaqueros. Del Puerto. Another Diamond Valley. Another Castaic. But the biggest opportunity for storage is to replenish the aquifers in the San Joaquin Valley. There’s plenty of room; the San Joaquin Valley’s total aquifer capacity is estimated to be several hundred million acre feet. And at a percolation rate of one foot every four days, 100,000 acres of distributed basins could store 2,250,000 acre feet in just three months.
Finally, the aqueducts themselves have to be fixed. They currently operate below capacity, thanks to land subsidence. This can be fixed however, as is being proven by the recent retrofits of the Friant-Kern Canal. And the cost for all of this? Staggering, but worth every penny. Figure about $10 billion to dredge up to 1,000 miles of delta and river channels. Allocate another $20 billion to construct or expand storage reservoirs, alternative diversion systems, and repair the aqueducts. The Delta Conveyance is officially estimated to cost another $20 billion, and if they’d just get on with it, they might come in on budget. Altogether, $50 billion is a ballpark estimate of what it might take to pay for new projects capable of harvesting another five million acre feet per year of fresh water either before or during its journey through the Sacramento-San Joaquin Delta.
The beauty of this vision makes bearing its cost worth considering. If an equal amount of investment went into urban runoff harvesting, wastewater reuse, and desalination, we could increase our water supply by ten million acre feet per year. With this much more water, we can do more than save our farmland and rehydrate our cities. The environmental upside is stunning and the dream bears repetition. We could have surpluses sufficient to refill Mono Lake, reclaim the Salton Sea, revitalize the Delta, remove effluent from the San Francisco Bay, and drain Hetch Hetchy to bring back Yosemite’s twin. This is the $100 billion grand water bargain. It’s time to talk less, and do more.
EDWARD RING: The cost and the upside of the “big gulp”
By Edward Ring, Director of Water and Energy Policy at the California Policy Center
A study published by the Public Policy Institute of California offers an answer to this question. They measured flows through the delta over a 37 year period through 2016 and classified the volumes of water into categories including diversions for farm irrigation and municipal use, flows essential to maintain the health of the delta ecosystems, and the intriguing category “uncaptured water.” They estimated the volume of “uncaptured water” to average 11.3 million acre feet per year over the 1980-2016 period.
It’s important to avoid concluding that 100 percent of this uncaptured water could be safely diverted. And since the 2017 PPIC study came out, new regulations have increased the amount of flow that would now be classified as required for ecosystem maintenance, proportionately reducing the estimate of uncaptured water that may be available. But it is worth examining what it would take to harvest an additional five million acre feet of water from the delta each year. Successfully accomplishing this requires at least three major initiatives.
First, the delta itself has to be reengineered to remove silt. For over a century, ever since the delta was channelized, farmers and government agencies dredged the rivers and sloughs. The soil was used to enrich fields and build levees. This all came to a halt starting in the 1970s, and now the regulatory burden confronting any public or private entity hoping to dredge is prohibitive. This must change.
Dredging the delta will restore deep and cool channels to help salmon migration and increase the volume of aquatic habitat. In a channel 200 feet wide with an average depth of three feet, the proposed dredging of 100,000 cubic yards per mile would nearly double the volume of water. The benefits are tremendous.
By significantly increasing the volume of delta channels, the rate of flow during heavy runoff is increased, meaning more water can be reserved in reservoirs. As it is, Sierra reservoirs are drained during winter so they retain capacity to accommodate rapid spring runoff. To the extent rates of flow are faster through the delta, more water can be safely saved in the reservoirs.
At the same time, increasing the volume of fresh water in the delta allows the existing delta pumps to operate longer at full capacity before they reverse the current and draw in salt water from the San Pablo Bay. The combination of higher volume and faster flow in the delta thanks to dredging means more water can be withdrawn without risking salt water intrusion.
The second step necessary to take the big gulp is to increase the volume and duration of water supplying the existing delta pumps, which only have a combined maximum capacity of 30,000 acre feet per day. That means even if they ran at full throttle for 100 days, they would only withdraw 3 million acre feet. The pumps need to run at higher rates for longer periods. More diversion capacity is required.
For this reason, the “Delta Conveyance” has dominated discussions of major water infrastructure investments for the last several years. This 45-mile-long, 40-foot internal diameter tunnel connecting the Sacramento River north of the delta to the Clifton Court Forebay to the south is a controversial and expensive proposal. But at a maximum throughput capacity of 20,000 acre feet per day, and a design that permits multiple points of diversion distributed across the delta, it would go a long way toward developing sufficient capacity to take the big gulp. There are proposals to supplement the delta tunnel with other creative means to divert large volumes of water out of the delta, but expanding diversion capacity brings us to the third requirement: distribution and storage.
Will the greater volume of water in the delta post-dredging, combined with a million acre feet or more additional water reserved in Sierra Reservoirs, combined with the delta tunnel’s ability to safely remove water from several points in the delta during an extended season, enable the delta pumps to operate at full capacity for 250 days a year? Because with the existing state and federal pumps, that’s what it would take to pull an additional five million acre feet per year out of the delta.
And if we can’t run the state and federal pumps at maximum capacity for 250 days per year, then what additional projects are necessary to enable the big gulp? Should we build another forebay and aqueduct, right down the center of the San Joaquin Valley, to help move water from the delta tunnel or other diversion projects? We should consider all options; some are surprisingly cost-effective.
We also have to recognize that pouring an additional five million acre feet per year into the state and federal water project aqueducts, or even into a network that added another aqueduct to the system, would quickly overwhelm available storage downstream. One solution would be to build and expand more reservoirs. Pacheco. Los Vaqueros. Del Puerto. Another Diamond Valley. Another Castaic. But the biggest opportunity for storage is to replenish the aquifers in the San Joaquin Valley. There’s plenty of room; the San Joaquin Valley’s total aquifer capacity is estimated to be several hundred million acre feet. And at a percolation rate of one foot every four days, 100,000 acres of distributed basins could store 2,250,000 acre feet in just three months.
Finally, the aqueducts themselves have to be fixed. They currently operate below capacity, thanks to land subsidence. This can be fixed however, as is being proven by the recent retrofits of the Friant-Kern Canal. And the cost for all of this? Staggering, but worth every penny. Figure about $10 billion to dredge up to 1,000 miles of delta and river channels. Allocate another $20 billion to construct or expand storage reservoirs, alternative diversion systems, and repair the aqueducts. The Delta Conveyance is officially estimated to cost another $20 billion, and if they’d just get on with it, they might come in on budget. Altogether, $50 billion is a ballpark estimate of what it might take to pay for new projects capable of harvesting another five million acre feet per year of fresh water either before or during its journey through the Sacramento-San Joaquin Delta.
The beauty of this vision makes bearing its cost worth considering. If an equal amount of investment went into urban runoff harvesting, wastewater reuse, and desalination, we could increase our water supply by ten million acre feet per year. With this much more water, we can do more than save our farmland and rehydrate our cities. The environmental upside is stunning and the dream bears repetition. We could have surpluses sufficient to refill Mono Lake, reclaim the Salton Sea, revitalize the Delta, remove effluent from the San Francisco Bay, and drain Hetch Hetchy to bring back Yosemite’s twin. This is the $100 billion grand water bargain. It’s time to talk less, and do more.
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