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Subconservancy district eyes alluvial fans as water storage areas

by Sheila Gardner

The Carson Water Subconservancy District gave its blessing to a $342,000 pilot project that, if successful, will create an underground storage system for excess Carson River water, a goal of the agency since it was formed in the late 1950s.

District directors listened Wednesday to a project outlined by Douglas Maurer of the United States Geological Survey water resources division.

“We can’t build surface reservoirs, we have to have a place to store water in abundant years,” said Ed James, manager of the subconservancy district.

Efforts to build a dam on the Carson River have been frustrated by environmental issues and funding, leading officials to look for underground solutions.

This project would take advantage of the Carson River’s extensive alluvial fan system. An alluvial fan is a triangularly-shaped deposit of sand and soil located at the base of a slope and formed by the flooding of tributaries to a larger stream or river.

n Deep fans. The fan system in Carson Valley is anywhere from 50 feet to 200 feet deep.

According to Maurer’s report, the alluvial fans provide potential sites for below surface storage of water that later can be extracted by wells for municipal supply or can augment the base flow to the Carson River or associated canals during dry periods.

That type of artificial recharge is a more cost effective alternative to surface storage with less environmental impact, according to Maurer.

James said the ideal site for the project would be U.S. Forest Service property, but “I probably won’t live to see the day the (permitting) process is covered. It’s not worth it.”

Two sites for the pilot project are where Pine Nut Creek enters the Carson Valley floor from the East and near the southernmost end of the Valley at Mud Lake.

“We’re doing this in Douglas County because so much legwork already has been done,” James said. “After we do the study, if it is successful, we could go develop the storage system at that site.”

Subconservancy district director Bernie Curtis asked what the project would look like and if it would create a wetlands area.

“Hopefully, when it’s completed, it will have some habitat enhancement,” James said.

A gravity meter, which Maurer said is the size of a lunchbox, will take measurements to determine the shape of the recharge mound and estimate the yield of the aquifer. The pilot project will develop a procedure to evaluate sites throughout the Carson River basin for adequacy of underground storage and determine if the deposits allow adequate percolation to the water table and provide a storage reservoir, Maurer said.

n Say, what? “The only thing he made reference to I understood was ‘lunchbox,'” joked CWSD Director Kelly Kite as Maurer discussed “subsurface lithology,” “geochemical reactions,” “microgravity stations” and “diurnal temperature variations.”

The study was hailed by director Greg Smith, comparing it favorably to a similar project in Carson City.

“There’s been so much success in Carson City,” Smith said. “You try to maximize the surface water as best you can by putting water back in the ground.”

The goal is to store 2,000 to 3,000 acre feet of water per year. An acre foot is the amount of water – 326,000 gallons – that will cover 1 acre to a depth of 1 foot.

The USGS will pay half of the costs for the 3-year project, depending on the availability of federal matching funds.

“This system has been in use in Europe for decades,” Maurer said.