Friday, December 21, 2007

Report: Valley water supply in decline

USGS study says declines can be seen both in surface water and groundwater supplies

Express Staff Writer

A study released this week by the Idaho office of the U.S. Geological Survey indicates a troubling downward trend in ground and subsurface water supplies in the Wood River Valley. However, the study doesn?t point to one single culprit to explain the declines. Photo by Mountain Express

Results from an exhaustive study released earlier this week by the U.S. Geological Survey indicate a downward trend in the Wood River Valley's groundwater and surface-water supplies.

The comprehensive study indicates that water levels in some parts of the valley are declining beyond what might be expected from typical, short-term fluctuations. The study was initiated by local governments and nonprofit groups pursuant to concerns about growth and the long-term sustainability of the area's water supplies.

A question that the 40-page report doesn't answer is whether the declines are due to drought, increased water use or a combination of both. However, the study's findings do provide a base on which future measurements can be built, allowing the valley's decision makers to document water-resource trends with greater confidence, a USGS news release states.

As part of the study, the scientists working for the federal agency analyzed groundwater and stream-flow trends and compared water-resource conditions from 1952 through 1986 with data they collected in October 2006.

The report's three authors—Kenneth Skinner, James Bartolino and Andrew Tranmer—examined data from three wells and three streamflow gauges for which long-term data were available. According to the USGS scientists, the data for all three wells show statistically significant downward trends in water levels. Data from one of the streamflow gauges also showed declines.

The other two streamflow gauges are located on local spring-fed streams, which the USGS scientists said makes them useful indicators of groundwater conditions.

"Data for those two gauges show decreasing flows during December, January and February," the USGS news release states.

Decreasing flows were apparently also evident at one of the gauges during the months of July through November and in April. Data for all three streamflow gauges show declining low-flow trends. Low flow at these gauges is fed primarily by groundwater discharge, the USGS scientists said.

In October 2006, the scientists measured water levels in 98 wells and stream flow at 13 different sites throughout the valley. They used those measurements to construct a groundwater contour map of the valley's aquifers. Using the available data for the period between 1952 and 1986, the scientists constructed a second groundwater contour map. They compared the two maps to determine changes in water levels. Those are represented on groundwater-change maps included in the USGS study report.

What local leaders will do with the results of the study remains unclear.

On Thursday, Blaine County Commissioner Tom Bowman said the county hasn't scheduled a meeting to discuss the results of the study or the land-use changes that may be needed in light of the information. He said that in the near term, the most appropriate thing to do may be to hold a joint townhall-style meeting with the Blaine County Commission and county Planning and Zoning Commission to discuss the findings.

Bowman said that while the study does indicate downward trends in the local water supply, it doesn't point to any one factor to explain those changes.

"There are so many factors," he said.

And the declines may not be attributable to residential development, Bowman said, because most indoor residential water use is considered "pass-through" in nature. That refers to uses of water such as showers, clothes washing and dishwashers, which once complete, send the dirty water to a septic tank or municipal wastewater treatment plant and from there to the river.

The bottom line is that no one knows the reason or reasons for the declines in the local water supply, he said.

"It could be precipitation, it could be development, it could be agriculture," he said. "We just don't have enough information."

The study was funded through a cooperative agreement between the USGS, Blaine County and the cities of Bellevue, Hailey, Ketchum and Sun Valley. Also helping to fund the study were the Idaho Chapter of The Nature Conservancy, the Sun Valley Water and Sewer District, the Blaine Soil Conservation District and local nonprofit group Citizens for Smart Growth.

The USGS is now working with local officials to develop a water budget for the area. Water budgets enable an accounting of water as it moves through the atmosphere, land surface and subsurface, the USGS news release states.

Bowman said the authors of the report will be in the Wood River Valley to hold a public open house on the issue sometime in January or February. He said the meeting will most likely be held at the Hailey Community Campus.

The USGS report, titled "Water-Resource Trends and Comparisons Between Partial-Development and October 2006 Hydrologic Conditions, Wood River Valley, South-Central Idaho," is available online at

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