Carson River flow remains steady
Growth in the Carson Valley during the past decade has not affected water outflow along the Carson River, a hydrologist with the U.S. Geological Survey told water officials this week.
Based on an outflow model, the same amount of water flowing through the river – about 303,000 acre-feet a year – has remained relatively unchanged.
“On the south end of the Carson River we are losing flow in the groundwater system and at the north end of the river we are gaining flow, so we are pretty much in balance,” said Doug Maurer, a hydrologist for the USGS.
Maurer wrote the original report describing the model in 1986 for the USGS. The outflow of the river has been monitored at a USGS gauge near Carson City since 1939.
Officials with the Carson Water Subconservancy District met with Maurer Wednesday to discuss water issues through the basin and to gauge possible effects of future growth and development in the Carson Valley.
While recent figures were unavailable for the average amount of water pumped in the Valley, the state’s estimate of pumping was about 26,000 acre-feet in 1994.
An acre-foot is enough to cover an acre of land in a foot of water.
About half of that was for agricultural use during a dry year.
“As far as we can tell without a detailed analysis, right now the pumping is having no measurable effect,” he said.
Water officials want to know how much water can be pumped out of the river before there is a downstream effect.
Maurer said it is a hard question to answer because the measured outflow has an accuracy rate of about 10 percent.
Continued growth in the Valley is expected to eventually impact river outflow.
“As you start pumping more, there will be a point where there will be a measurable change,” Maurer said.
Gauging any change is difficult because the long-term average outflow can be affected by long periods of drought or above-normal precipitation.
The only clear way to see the effects is to measure, over time, the outflow of the river annually. Included in the ground-water flow model is precipitation levels in the Sierra and how much runs off to recharge Carson Valley.
Even with future growth, the Carson Valley may be far from reaching that threshold, he said. Land being taken out of irrigation for development offsets the effect of pumping, so there is a tradeoff, he said.
But in a worst-case scenario, where the region could face several drought years in a row, there could be a decreased flow downstream, affecting population centers such as Dayton and Fallon.