HANFORD – The ground is sinking near Avenal and Corcoran, and the drop is damaging the California Aqueduct, according to a report released this week from the California Department of Water Resources.

The report identified agricultural groundwater pumping alongside the Aqueduct in a section near Avenal as the cause of a buckle in the Aqueduct's cement-lined channel.

The report says the buckle is causing a 20 percent loss in the Aqueduct's capacity to carry water.

The sinking phenomenon is known as subsidence. As water is pumped out of underground layers, those layers compress, causing the ground surface to sink.

That loss in Aqueduct carrying capacity could force operators of the State Water Project, which delivers water via the Aqueduct to thirsty Southern California, to limit flows to water project contractors south of Kings County at a time when they are expecting to receive nearly their full allocation due to a wet winter.

The report indicates that the center of the sinkage area dropped more than two feet from July 2013 to July 2016.

DWR officials are hinting at the possibility they might limit groundwater pumping in the vicinity of the Aqueduct to try to prevent further damage.

That's raising fears in Kings County of harm to pistachio, almond, citrus and other farming operations in the Avenal/Kettleman City area.

Farms critical to the local economy have relied on groundwater during the last several drought years.

"If we hadn't used the wells over the last three years, everything would have died," said Mike Kochergen of Kochergen Farms. "If they were to shut the wells down, that would be devastating."

Kochergen's family grows citrus and almonds in the area.

Former Avenal mayor Harlin Casida said that any DWR action would also likely affect Keenan Farms, a major pistachio grower in the area, as well as other growers.

Bob Keenan, president of Keenan Farms, couldn't be immediately reached for comment.

"Six years of drought has caused them to really overdraw water out of the aquifer," Casida said. "There's quite a few smaller farmers in there who could be affected."

DWR official Jeanine Jones said that the satellite data and aircraft imagery used to measure the sinking can also pinpoint individual wells that are causing the ground to fall.

"There are literally thousands of wells within a couple miles of either the [Eastside Bypass] or the Aqueduct," Jones said. "We need to find a way to control subsidence near our critical water infrastructure. We need to do something."

The Eastside Bypass is a flood control system designed to shunt San Joaquin River water northward away from Fresno during high flows. DWR officials are concerned that subsidence may have compromised the channel's flood control ability.

The report also mentions a broad area of subsidence centered on Corcoran that dropped about 22 inches from May 2015 to September 2016.

Jones said that engineers working with the California High-Speed Rail Authority have determined that the old Tulare Lake bed is tilting eastward because the ground is sinking faster in Corcoran than it is in the bottom of the old lake bed further west.

In super-wet years like the winter of 1997-98, portions of the old lake bed, which was drained for farming decades ago, fill up with water.

That raises the question of whether the sinking in Corcoran increases the city's flood risk in wet years. The city is located near the historic shoreline of the old lake.

Dustin Fuller, manager of the Cross Creek Flood Control District, said that the Cross Creek levee that helps protect the city from flooding when the lake starts to fill was raised four feet last year to counteract subsidence.

"We know that subsidence is occurring," he said. "The district decided it was prudent to raise it."

The levee as it appears today was constructed in the 1980s, according to Fuller. Fuller said there was a levee before that, but work done in the '80s substantially modified it.

He said that from the time of its construction until 2016, the top of the levee dropped about nine feet in elevation due to subsidence.

"The district is confident that the community of Corcoran will be protected barring a major catastrophic event," Fuller said.

The reporter can be reached at snidever@hanfordsentinel.com or 583-2432. 

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