Presenters paint future concerns for water use

Commissioners from Churchill and Lyon counties met Monday in Fallon to hear presentations on upstream and downstream water issues affecting the Carson River and another on the Humboldt River.

Presenters discussed issues pertinent to the Carson River corridor, and they included Chris Mahannah of Mahannah and Associates, Kip Alexander of the U.S. Geological Service and Mike Workman from Lyon County.

“Growth has come to Nevada, and we’re all concerned with this,” said Mahannah, the first presenter.

He said it was prudent for commissioners and the public to understand and work together with water problems and minimize the conflicts rather than having the courts decide the issues. Mahannah focused his presentation on the four basins divided within the Carson River watershed between the east slope of the Sierra Nevada and Lahontan Reservoir.

Mahannah said current concerns are involving severely appropriated basins, domestic well use, conjunctive management and mitigation of impacts to avoid conflicts. He raised concerns about the Carson River basin, which includes Silver Springs.

“There’s a large concentration of domestic wells in Churchill Valley and a large concentration along the river corridor,” he said.

During his presentation, Mahannah discussed how groundwater replenishes itself and the connection of ground and surface water.

Alexander, a supervisory hydrologist with USGS, discussed the Carson River’s future. His overview examined hydrologic water models, the groundwater monitoring network, stream gauges and a summary of the 2017 runoff. He also described the concepts of groundwater, its movement and storage. He said aquifers are vital to the watershed and part of the groundwater system that can be developed and supply water to wells. Alexander added there are many groundwater users within the watershed.

Hydrologists like Alexander are concerned about changing weather patterns and climate warming. A collaborative project of the Carson and Truckee rivers is looking at future climate variability and testing alternative management approaches. In his presentation, he said “streamflow is simulated for climate scenarios, and the results are passed to downstream models, which also test different management strategies to adapt changing supply characteristics.”

The one segment of Alexander’s discussion centered on projected climate changes at Lake Tahoe and projected growing season lengths for the Carson Valley. Developed models are looking at air temperatures at increasing at 5 or 10 degrees Fahrenheit. Alexander said a temperature rise of 5 degrees in the RCP 4.5 model would see base greenhouse emissions peak in 2040, while 10 degrees in RCP 8.5 will result in emissions rising through the end of the century.

Alexander, though, said precipitation is not showing a trend.

“It may not be wetter or drier,” he said.

With the warmer temperatures, though, he said the growing season could result in 40 additional days under the first model and 60 days or longer if temperatures rise 10 degrees. As temperatures increase, Alexander said runoff would occur earlier.

“Less flow later in the year may be harder to support agriculture,” he said.

The research shows users may expect warming snowpack losses, longer growing season and increased evaporative demands. Alexander said the largest precipitation changes will increase the number of dry days and increase large storms with modest changes in small to medium storms.

Workman, public works director for Lyon County, gave an assessment for the Mound House and Dayton service areas that serve 6,800 water customers and 5,900 sewer customers. He also noted many older wells in the area are located within 200 to 500 feet of the Carson River. Workman said Lyon County has a 16-inch interconnection with Carson City.

“We share a 3 million gallon storage tank,” he said, adding during the past 10 years, no major operational issues have occurred.