Groundwater depletion sinks portions of Cedar Valley

Published: Monday, March 31 2014 2:53 p.m. MDT

Too much groundwater pumping in Iron County's Cedar Valley is causing the land to sink and crack with the subsidence creating significant "fissures" in an urbanized area of Utah for the first time.

Utah Geological Survey

SALT LAKE CITY — Over-pumping of groundwater from a deep aquifer in Cedar Valley for the past three decades has caused the ground to sink and crack, inflicting damage on a would-be subdivision and putting future development at risk.

The mining of the aquifer — taking more water out than can be replenished — has already led to a moratorium on new allocations of water by the state engineer and may ultimately lead to harsher measures for existing water users.

"There's no way to make the ground go back up," said Boyd Clayton, Utah's assistant state engineer over water rights. "The limits would depend on how much worse it gets."

A just-released report from the Utah Geological Survey shows the ground has been sinking in some areas around Cedar City for decades. The 116-page report said the pumping has lowered the water table in the Cedar Valley aquifer by as much as 114 feet since 1939.

"They don't have a lot of water. It is a deep aquifer system that has a limited recharge, and they are using as much or more water than is being recharged into the system," Clayton said.

Tyler Knudsen, project geologist with the survey, said clay sediments and fine-grained silts over time become compacted due to water withdrawals, causing the land to sink.

The subsidence has caused a total of more than 8 miles of earth fissures to form in a 100-square-mile area of the valley. The damage was first noticed in May 2009 in a partially developed subdivision.

"Enoch City reported what they thought was an active fault disrupting the pavement, sidewalks, and curbs and gutter in a rather large subdivision," he said. "The fissure ran through the middle of several lots."

Knudsen added that the discovery marks the first time in Utah that an urbanized area has been impacted by ground subsidence and fissures — which have been responsible for tens of millions of dollars in damage in places such as North Las Vegas, Nev., California, and Texas.

The report, compiled with the support of the Central Iron County Water Conservancy District, noted that an annual average of 600 acre-feet of water has been pumped from the Cedar Valley since 1964.

Agricultural withdrawals make up the vast majority of that water use, though that has changed somewhat over time — from 96 percent in 1964 to 74 percent in 2008.

The report suggests possible aquifer management options to bring average annual groundwater discharge and recharge into balance to stop more damage from playing out.

Other areas that have had the problems — such as North Las Vegas and Murrieta, Calif. — require fissures and subsidence to be part of the consideration for any new development.

Enoch city manager Rob Dotson said the same type of restrictions will be in effect should there be any interest in developing impacted areas.

"They will have to come to us with a plan that works," Dotson said.

Email: amyjoi@deseretnews.com, Twitter: amyjoi16

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