FTR News

Driggs, Idaho - (04/08/2004) -

Most of us here in eastern Idaho are intimately familiar with the H2O molecule in its various forms; rivers to fish, lakes to swim in, rain to water our crops and gardens, snow to ski on, and icy roads to avoid when we’re driving. All these kinds of water are part of our daily lives; there is, however, another type of water that is equally important but largely invisible. Groundwater flows beneath the earth’s surface and is contained in subsurface aquifers (in an aquifer the empty spaces between rocks are filled with water). This unseen form of water is vitally important; not only does it provide clean drinking water and precious irrigation water but is a huge reservoir that feeds our lakes, rivers and wetlands. The Eastern Snake River aquifer, between Ashton and a Thousand Springs, Idaho, covers more than 10,000 square miles and contains an estimated 100 million acre-feet of water.

In the Teton Valley we also have a large reservoir of underground water that lies below the layer of gravel covering the valley floor. The amount of water in this aquifer is a result both of recharge (water going in) and discharge (water going out). Water flows into the aquifer from rain, snowmelt, irrigation water, and streams crossing the valley floor. Water is taken out of the aquifer for domestic and irrigation use; it also leaves the aquifer and flows into the Teton River and spring creeks on the valley floor. Because water use in the Teton Valley has changed dramatically over the past 120 years the amount of water in our aquifer has also changed.

At the turn of the century, as the Teton Valley was settled, the practice of flood irrigating farmland with generous amounts of early spring runoff was instituted. An extensive system of canals and ditches was built to deliver water to cultivated fields, water was turned out onto those fields, and covered the ground throughout the spring and early summer. Water that wasn’t taken up by plants or evaporated percolated into the ground and as a result groundwater levels throughout the valley began to rise. In the 1970’s however, a second change in water use occurred; irrigation technology advanced and farmers began to use sprinkler instead of flood irrigation, which enabled them to irrigate larger areas of ground with less water.

Now, in 2003, as more land is taken out of agriculture and developed, and after 5 years of drought, we are just realizing how dramatic the effects of this second change in water use have been. Water levels in wells throughout the Teton Valley have been dropping and many homeowners have had to drill deeper to get domestic water. Additionally, flows in the Teton River have changed; the number of low flow days, below 150 cubic feet per second (c.f.s) has increased since 1980, flows in spring creeks are declining, and wetland areas are decreasing. Foster Slough that used to carry boats up and down it is no longer easily navigable; ground where waders were once needed to walk is now traversed in sneakers.

In 2002 Dr. Michael Nicklin and Cascade Earth Sciences completed the Groundwater Model for the Upper Teton Watershed; a study initiated by the Teton County Commissioners and funded by Teton County, Friends of the Teton River, the cities of Driggs, Tetonia, and Victor, Idaho Department of Environmental Quality, and U.S. Geological Survey. The study compiled all the available Teton Valley water use data and modeled how the aquifer system works. The model found that the aquifer system is highly dependent on recharge both from irrigation and precipitation. Additionally, although the aquifer does have substantial water bearing capacity, there are areas within the whole system that have more limited capacity. Areas in the valley that show potential water limitations include: areas that are highly dependent upon recharge from irrigation (in the event that irrigation decreases significantly), areas nearer the toes of the mountain, and areas between, rather than close to, tributary streams.

Friends of the Teton River (FTR) has funded further studies with Michael Nicklin to better understand how the aquifer functions on a smaller scale in places that are potentially vulnerable to lowered water table levels; these will be completed in the fall of 2003. Additionally, FTR is sponsoring two groundwater recharge demonstration projects this spring, which will assess the feasibility of large-scale recharge efforts. One of these projects will involve spreading snowmelt runoff water over an area and monitoring how much and how quickly groundwater levels rise in the vicinity of the project. The other project will monitor the groundwater recharge rate as a gravel pit is filled with water. The projects have received a great deal of input from irrigators in the valley and FTR will make all the pertinent information available to the public on their website. If you have any questions about the groundwater study or the demonstration recharge project please call the FTR office at 354-3871.