Water study not much help in determining growth cap

A study by the United States Geological Survey concerning water consumption and recharge does not determine pumpage, one of the figures some say is important in determining a growth cap in Carson Valley.

Doug Maurer, a hydrologist with the geological survey, said the report will be forwarded to the state engineer who will determine how much pumpage the Valley can support.

"The range we came up with is fairly similar to what the state engineer's office has been using, so the numbers might not change much at all," Maurer said.

Initiated in February of 2003, the report addresses concerns over continued growth in Carson Valley, a joint effort between Douglas County and the United States Geologic Survey.

From 1990 to 2005, annual recharge of water Carson Valley's water coming from streams, rivers, precipitation and more ranged between 35,000 and 56,000 acre-feet according to this report.

In a previous report, the potential recharge in Carson was listed as 49,000 acre feet per year, Maurer said.

Discharge, or water used for everything from irrigation and domestic use to that dissipated through evaporation, is estimated at between 41,000 to 44,000 acre-feet annually, according to this newly-released report.

Between the water coming in and that going out are a tangle of factors impacted by population and land use.

Along the eastern side of Carson Valley, areas of increased growth where recharge is limited to groundwater flowing from the Pine Nut Mountains, water levels in tested wells have dropped from five to 10 feet, according to the report.

Water in at least three wells tested there have declined 20 feet since the early 1990s, likely caused by the discontinued use in 1997 of a nearby reservoir.

Conversely, a well tested near the mouth of Buckeye Creek along Carson Valley's eastern fringes has risen 20 feet, most likely due to infiltration from an effluent reservoir nearby.

Water levels in wells near the valley floor show little long-term rise or decline from 1977 to 2006, suggesting that part of Carson Valley is in a state of dynamic equilibrium, according to the report.

A planned land-use change that would convert 350 acres from agricultural to residential or commercial use would reduce the amount of water loss through evapotranspiration, that lost from the soil by evaporation and transpiration from plants, by 1,000 acre-feet per year.

If the irrigation water that once served those fields is piped, the loss of recharge, a measure critical to maintaining the valley's aquifer, would be 900 acre-feet per year.

"The change in land use is likely to increase the runoff of precipitation from impervious surfaces, but the effect of this change depends on the use of storm-water drainage," the report said.

If the water normally returned to the aquifer is lost, Nevadans downstream would likely benefit, with an estimated 2,000 acre feet per year going downstream in the Carson River.

In cooperation with Douglas County and the Subconservancy District, the Geological Survey is continuing work on a numerical grounwater flow model of Carson Valley, planned for completion in 2008.

The 64-page report is available on the Web at nevada.usgs.gov/wateractivities.htm.

Susie Vasquez can be reached at svasquez@recordcourier.com or 782-5121, ext. 211.