A substantial portion of the groundwater used in the Carson Valley keeps its fields green during drought years.
That explains why in a dry year like 2004, pumping of groundwater neared the recharge limit of 35,000 acre feet. In a wet year like 2005, the amount of groundwater being pulled out of the aquifer decreased by about a fifth to 27,000 acre feet, according to Jason King of the State Engineer's Office.
King was one of a half dozen speakers at a water symposium Saturday, hosted by the Sustainable Growth Initiative Committee. An estimated 250 people turned out to learn about water in Carson Valley and how it relates to the Carson River.
The Carson River watershed is the largest in the Eastern Sierra Nevada, according to the Nature Conservancy's Laura Crane.
"The Carson River really is our lifeline," she said.
While state and federal law makes a distinction between surface and groundwater, the Carson River supplies 70 percent of the water in the Valley's aquifer, according to U.S. Geological Survey hydrologist Doug Mauer.
"There is a very close connection between the river and groundwater in the Valley," Mauer said. "The average depth to groundwater is 5 feet."
The valleys along the east slope of the Sierra tend to get the majority of the moisture, and provide the majority of the water that goes into the river, which turns east into drier areas where users also claim rights.
Because of the close connection between the river and the aquifer, pumping ground water affects the amount of water left in the river, so that in dry years, the Carson dries up in the fall.
According to Truckee River Flood Project Director Naomi Duerr, rights to the water are determined by beneficial use and by when the rights were obtained.
"First in time is first in line," she said.
Water law in Nevada is designed to get water where it will be used.
"The idea is to put the water to work," she said. "If you don't use it, you'll lose it."
Surface water rights are a property right that can be separated from the land, but are assumed to go with the land. Groundwater rights follow the surface water right, according to King.
During wet years, agriculture uses surface water to irrigate fields, but in dry years, ground water rights are used to make up for the shortage in surface water.
A plan in Lyon County to take surface water early in the season and inject it into a well to be used later has drawn concern from Churchill County downstream.
Subconservancy District Chairman Ed James said he saw the Carson River as a single watershed.
"We're not promoting growth," he said. "We're using existing water plans and local entities and looking at it all regionally."
James said global warming will tend to start the water season a month earlier by 2099 at the present rate.
"We're seeing more rain on snow events earlier in the year," he said.
That means agriculture will be pumping groundwater earlier to make up for the shortage in surface water as the summer progresses.
James proposes building a pipeline between Carson Valley and Carson City so the capital can pump water it has purchased.
"We just want to use the resource they have a legal right to," he said. "We're not taking water from one community to another."
There are 96,641 acre-feet of paper groundwater rights in the Carson Valley. The recharge rate in the Valley is estimated at 35,000 acre feet. The state engineer uses that number to determine when people begin mining water.
