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Subsidence shrinks Friant-Kern Canal capacity by 60 percent

Friant-Kern Canal repairs
Crews seal seams in the concrete-lined Friant-Kern Canal north of Bakersfield, Calif. ahead of major work to restore flows through a section impacted by land subsidence.
Friant Water Authority embarks on three-phase plan to restore canal flows to design capacity and boost deliveries to impacted irrigation districts

Subsidence along the Friant-Kern Canal is nothing new. However, a five-inch drop within the past year in southern Tulare County is troublesome as it caused a 60 percent reduction in deliveries to districts along the lower half of the canal system.

Canal capacity in the area is now about 1,750 cubic feet per second, down from a designed capacity of 4,000 cfs.

Douglas DeFlitch, chief operating officer for the Friant Water Authority, says evidence of subsidence was noticed last year when the canal was at capacity because of flood releases. Friant officials noticed the problem when they discovered water that should have been freely flowing under a bridge was instead pushing against it.

Surveys conducted between April and August of last year confirmed the severity of the subsidence, a result of increased groundwater pumping from about 2012 through 2016. The groundwater pumping came in response to reduced and curtailed surface water deliveries by the Bureau of Reclamation during the period.

Friant Water Authority conveys federal Central Valley Project (CVP) water from Millerton Lake near Fresno to irrigation and water districts from Chowchilla to Arvin as part of a contract the Bureau of Reclamation has with water users. Friant is a joint powers authority with 15 member districts that manages and maintains the 152-mile long gravity-fed system for the bureau.

In 2014 and 2015 the Bureau of Reclamation cut all water deliveries to districts in the Friant system. This forced farmers to pump available groundwater just to keep permanent crops like citrus, tree nuts, grapes and blueberries alive. Some growers along the eastern edge of the San Joaquin Valley lost hundreds of acres of citrus and other orchards for lack of water.

For those that could pump water they did, creating ripple effects in the region that left domestic wells dry and caused homes in Porterville to go without running water for three years until Tulare County could make a permanent fix.

Farm impacts

For farmers from southern Tulare County to Arvin, this decline in canal capacity means reduced surface water supplies and greater reliance upon groundwater – a problem the state of California says it wants to fix through last year’s passage of the Sustainable Groundwater Management Act (SGMA). In short, the act will limit groundwater pumping to achieve long-term sustainability of aquifers, which have been in decline for decades.

DeFlitch says Friant has a plan to address subsidence and the impacts it is having in the region, but that will take sustainable deliveries of surface water to achieve. This plan will be unfolded in three phases, he says.

The first phase, which includes sealing joints in the lined canal system and surveying five county bridges in the region to determine whether they need to be raised, should be complete by April.

The sealing project was borne out of a six-foot raise in the canal banks after the 1977 drought \ caused significant subsidence in the region. Raising the canal banks by six feet then did two things: increased carrying capacity in the canal and added “freeboard” space, which is the desired safe space above that canal capacity regulators want to protect canal banks. Because of subsidence, that freeboard space can now be encroached upon during high flows in the canal. Aside from delivering water during irrigation season, the canal is also used for flood control to relieve pressure on Millerton Lake during high inflows on the San Joaquin River.

The second phase will include about $20 million in repairs through fiscal year 2019. That could include bridge work in concert with Tulare County, along with other repairs to the canal system.

Long term repairs beyond that could cost about $350 million, which DeFlitch says Friant hopes could come through a new water bond under consideration. These long-term fixes, DeFlitch says, cannot happen without state and federal money.

“This is a good bill that would benefit a lot of the districts in the Friant system by being able to get the Friant-Kern Canal back to its maximum capacity,” DeFlitch says.

One such long-term fix could include a cross-valley canal, which would link the California Aqueduct (State Water Project) with the Friant-Kern Canal (CVP). Cost of that canal will depend on where it is constructed as the California Aqueduct flows along the western edge of the San Joaquin Valley while the Friant canal is on the eastern edge of the Valley.

Yet another benefit to the Friant-Kern Canal is its ability to feed several groundwater banks in the southern end of the Valley. These banks will help achieve goals of SGMA, but can only work if sustainable supplies of surface water are maintained, DeFlitch says.

TAGS: Water
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