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Irrigation causes variation in water use

The East Fork of the Carson River just upstream from Lutheran Bridge is flowing on Thursdy, but just barely. Most of the water is diverted for irrigation.
Kurt Hildebrand

Carson Valley is one of the few places in the Carson River watershed where agriculture uses as much groundwater as its municipalities.

Supplemental water rights, which is groundwater agriculture can pump to make up for years when there isn’t enough water in the river, make up half the roughly 100,000 acre feet of paper water rights in the Valley.

That compares to a perennial yield of 49,000 acre feet available from the Valley’s aquifer, according to the Carson Water Subconservancy.

On Wednesday, Subconservancy Director Ed James is scheduled to conduct a presentation at the Minden Town Board. That meeting starts at 5:30 p.m. at the CVIC Hall in Minden.

Past studies show Valley residents seldom pump more than 35,000 acre feet, even in dry years when ranchers are firing up their agricultural wells.

“Ranchers typically don’t want to pump those wells because it’s more expensive,” James told Douglas County commissioners during a similar presentation July 16.

James showed commissioners a chart that detailed the connection between flows in the Carson River and the amount of groundwater pumpage over the years. When there’s plenty of water in the river, the amount of water pumped goes down, while it goes up in dry years.

Supplemental agricultural rights are required to pump.

While every basin in Nevada is overallocated when it comes to water rights on paper, only a few are actually mining water something that Nevada law prohibits.

James pointed out that in Silver Springs there are 10 times more paper water rights than actual water.

James said the U.S. Geological Survey is conducting a study of the Humboldt River basin to determine just how much water is available there.

At issue for several groundwater basins in the Nevada deserts are the number of domestic wells.

While Carson Valley residents with wells use only around 4,000 acre feet of water or 11 percent of the total, well owners in Churchill Valley downstream account for around 60 percent of the water used there.

All of Carson Valley’s water purveyors use an average of 8,495 acre feet a year, compared to Carson City’s 11,078 acre feet a year.

The Gardnerville Ranchos has shown a decrease in the amount of water used, James said, due in part to the implementation of metering in Douglas County’s largest community.