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Keeping the Salt Field at Bay II

By Robin Meadows

Keeping the Salt Field at Bay I

After four of California’s driest years on record, the rain we’ve gotten this winter is hardly a drought buster. But it’s still a relief. Just a year ago, our “wet” season was so dry that state water officials panicked.

Major reservoirs were drawn way down, and record-low snowpack would limit replenishment to a trickle. Water managers worried about the hot, dry months. Would reservoirs still hold enough for freshwater releases to keep saltwater from pushing deep into the Sacramento-San Joaquin Delta, contaminating water supplies to cities and farms? So they built a barrier to block salt instead.

False River emergency salinity barrier. Photo: Bird's Eye View
False River emergency salinity barrier. Photo: Bird’s Eye View

Late last spring, when all hope of snow was gone, the state Department of Water Resources (DWR) dropped 150,000 tons of rock across the West False River in the heart of the Delta. Salt barriers are not new. The state first built them in the Delta during the mid-1970s drought — two in 1976 and six in 1977 — and came close again two years ago. “We thought about installing a drought barrier in 2014 but then it rained,” says Eli Ateljevich, a water quality modeler with DWR. “2015 was more urgent. It was full of unpleasant surprises, like even when it rained not much was getting into reservoirs.”

While barriers are nothing new in the Delta, last year’s approach was. Rather than the multiple barriers used before, modeling suggested that a single obstruction would be less disruptive to fish habitat while still being enough to protect water supplies. With all the waterways that thread the Delta, it may come as a surprise that blocking just one could keep the salt at bay. But the West False River is effectively all that stands between the tides and the pumps at the southern end of the Delta. “It’s the biggest, most direct channel for getting salt down toward the pumps,” Ateljevich says. “Other routes are smaller, more meandering.”

West False River is the entrance to Frank’s Tract, a flooded island in the middle of the Delta that looks like a lake. “During drought, salt starts moving in and laps its way up to Frank’s Tract, and then the vigor of the tides injects it in,” Ateljevich says. And from there, it’s just about as close to a straight shot south as you get in the Delta — and water can take several routes. “Once salt makes it to Frank’s Tract, there’s no way to control it and keep it away from the pumps,” he adds. “The drought barrier was an insurance policy.”

One that we needed, it turned out. In the summer of 2015, salt levels just west of the barrier climbed as high as Ateljevich has seen since they’ve been intensively monitored. But inside Frank’s Tract, salt levels held steady and even dropped a bit. “Salt would have been just shy of twice as high without the drought barrier,” he says. “I’d give it an A+ for preventing salinity intrusion.” That said, he says there’s room for improvement: “I’d have liked the water to get fresher faster.” One way to make that happen in the future would be to get the barrier in before the salt intrudes so far into the Delta.

DWR reports that by keeping salt out of Frank’s Tract, the barrier helped us keep about 29 billion gallons in upstream reservoirs, instead of releasing it to flush out the Delta and keep the water drinkable and fit for farming. This much-needed water helped stretch supplies for people and fish until the next rains.

The barrier also provided a deeper look into the inner workings of the Delta. “We don’t often do these kinds of grand experiments on water flow and the ecosystem,” says Sam Harader, a manager with the Delta Stewardship Council’s Delta Science Program. So he and other Delta experts put their heads together to brainstorm likely impacts of the barrier. Then the program funded studies to see what actually happened.

Questions included whether altered flows would affect phytoplankton growth, and whether the barrier would restrict zooplankton — which the endangered Delta smelt (Hypomesus transpacificus) and other fish eat — from reaching the western Delta. Researchers also wondered if the difference in salt levels on either side of the barrier would affect which species of invasive clam lives where: the overbite clam (Corbula amurensis) thrives in brackish water while the Asian clam (Corbicula fluminea) does not.

“Part of the challenge, and really it’s a nearly impossible task, is teasing out the effects of the drought barrier from those of the drought,” Harader says. “Flows were already greatly reduced with or without the barrier.” The researchers are still crunching the numbers to see what it all means.

High speed maps of nitrate [NO3 (mg/L)], chlorophyll-a fluorescence [fCHLA (μg L-1)], and specific conductivity [SPCond (uS/cm) or in simplistic terms saltiness + dissolved solids] measured September 14, 2015 in the Stockton Deep Water Shipping Channel. Color bars show concentration of each measured concentration (green lowest, orange highest). Chlorophyll-a, nitrate and specific conductivity concentrations are all seen increasing in the south channel. Source: USGS, Downing, 2014 pers.comm
High speed maps of nitrate [NO3 (mg/L)], chlorophyll-a fluorescence [fCHLA (μg L-1)], and specific conductivity [SPCond (uS/cm) or in simplistic terms saltiness + dissolved solids] measured September 14, 2015 in the Stockton Deep Water Shipping Channel. Color bars show concentration of each measured concentration (green lowest, orange highest). Chlorophyll-a, nitrate and specific conductivity concentrations are all seen increasing in the south channel. Source: USGS, Downing, 2014 pers.comm
The Delta Science Program also funded a U.S. Geological Survey (USGS) study that gave snapshots of water quality in the Delta. “We’ll be able to link water quality data with biological data on algae, plankton and fish,” says USGS hydrologist Bryan Downing, who led the study.

While zooming along at 20 miles per hour, the boat used for the study sucked up water samples and pumped them through waterproof case-clad instruments, which took measurements every second. “It’s a great system,” Downing says. “We can cover lots of the Delta in real time, which is important because the Delta is tidal so water there is in nearly constant motion.” A given “parcel” of water can move miles across the Delta in six hours.

Besides confirming that the salt barrier worked, the study yielded a surprise. A set of findings pointed to troubles in the San Joaquin River-Stockton Deep Water Ship Channel, which links Disappointment Slough in the central Delta and to the eastern edge near Stockton.

One trouble was a huge increase in chlorophyll, which is a proxy for algae. And high algae can cause low oxygen, which is bad for fish and other aquatic life. A second trouble was that nitrogen levels tripled in the shipping channel, which makes sense because lots of nutrients can mean lots of algae. Completing the triple whammy, flows appeared to stagnate in the shipping channel. “Water seems to just sit there,” Downing says. “This part of the survey had a huge wow factor — we didn’t realize how extensive it was.”

Six months after the salt barrier went in, the state took it out and ended the grand experiment in the Delta. The barrier was massive at 750 feet across and 120 feet wide at the base, and deconstruction — crane bucket by crane bucket — took nearly 10 weeks during the fall of 2015. We probably won’t need a salt barrier this year because recent rains have begun to refill our reservoirs. But all that rock is sitting in Rio Vista, ready for the next time we need it to keep salt at bay in the Delta.

CONTACT Eli.Ateljevich@water.ca.gov; bdowning@usgs.gov; or sam.harader@deltacouncil.ca.gov

Keeping the Salt Field at Bay I, March 2014, ESTUARY News,  http://www.sfestuary.org/salt-field/

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About the author

Robin Meadows is an independent science journalist in the San Francisco Bay Area. She covers water and climate change adaptation for Estuary News, is the water reporter for the Bay Area Monitor, and contributes to Bay Nature, Frontiers in Ecology and the Environment, PLOS Research News and Water Deeply. Robin also enjoys hiking and photography.