Groundwater rights ruling hangs by single vote

A slim majority on the Nevada Supreme Court distinguished between senior and vested water rights holders in upholding the only approved groundwater management plan in the state.

Vested ground water rights are at least 110 years old while senior rights are younger and are subject to the plan for Diamond Valley in Eureka County approved by the State Engineer, justices said in a 4-3 ruling.

Diamond Valley was designated a critical management area in 2015, which requires the State Engineer to establish a means to reduce pumping through curtailment or a management plan.

“Diamond Valley in Eureka County is over appropriated and has been pumped at a rate exceeding its perennial yield for over four decades,” according to court decision, with 76,000 acre-feet withdrawn from a basin that has a perennial yield of 30,000 acre-feet.

There are 126,000 acre-feet of paper water rights in the basin, more than four times the actual recharge.

Under Nevada water law, mining ground water is prohibited, and the priority for pumping water is based on seniority.

In the case of Diamond Valley, that would mean that anyone with rights after May 1960 would be subject to curtailment.

The question before justices was whether the state engineer’s groundwater management plan supersedes priority, and the majority of four said it does, if the rights were appropriated after 1912. 

However, most of the majority decision hung partially on the fact those challenging the plan failed to present any evidence that their rights would be impinged. 

Written by Justice Jim Hardesty, the burden of proof was on the senior water rights holders to show their pre-1913 vested rights would be affected by the plan.

“Our holding does not preclude respondents from asserting a future constitutional claim if the (plan) actually affected their vested rights,” the majority held. “We reiterate that our holding is limited to nonvested water rights.”

The ruling is academic in most of Nevada’s water basins, because before curtailment could take effect, the state engineer would have to determine water users were exceeding groundwater recharge for 10 consecutive years, something that hasn’t been determined for any other basin in the state.

About a fifth of the Carson Valley aquifer’s annual estimated recharge of 52,500 acre-feet is directly related to the river, with 38,000 acre-feet the result of precipitation in the Valley, according to the U.S. Geological Survey.

An acre-foot equals 325,851 gallons. 

Carson Valley’s drinking water comes entirely from the aquifer, which doesn’t require the treatment surface water would.

Irrigation helps recharge the aquifer, but in dry years it can also put a dent in the aquifer. When water from the river is no longer available, irrigators have access to supplemental rights, which allows them to pump groundwater.

On paper, there are 49,000 acre-feet of supplemental rights available for irrigators, while municipal water rights account for about 38,000 acre-feet of ground water.