Friday, December 21, 2012

Report: Plenty of water for McHanville

Expert says development of area would not impact aquifer

Express Staff Writer

A water engineer reported this week that he believes there is a sufficient water supply to develop the McHanville area south of Ketchum, next to St. Luke’s Wood River. Photo by Mountain Express

The McHanville area south of Ketchum could be adequately supplied with water even if fully developed at the highest allowable density, a water engineer told local officials last week.

Charles Brockway, owner of Twin Falls-based Brockway Engineering, told members of the Ketchum City Council and the Blaine County Commissioners on Dec. 11 that a fully developed McHanville would deplete the aquifer, but not enough to “significantly” affect other users.

However, he warned, that might not prevent opposition to development from other water users.

“Any time you use the word ‘significantly,’ you’re going to get into an argument,” he said with a laugh.

Brockway was commissioned to conduct the water supply-and-demand analysis by Blaine County, the city of Ketchum and the Sun Valley Water and Sewer District. Its purpose was to determine what kinds of demands would be placed on area water supply if the McHanville area—which the county has designated for development of affordable housing—were to be completely developed.

The area includes St. Luke’s Wood River, a developed light industrial area, The Meadows mobile home park and the partially completed Quail Creek development.

Currently, the developed parts of the area are served by the city of Ketchum, the Sun Valley Water and Sewer District, and the Mid Valley Water Co.

Brockway’s study assumes development to maximum density—15 units per acre, which would result in 986 new units and an area population of roughly 2,900 residents.

“You might say that’s never going to happen,” he said. “But I can’t tell you. You people up here do strange things.”

Brockway also estimated maximum demand by using a number chosen based on the demand during peak season for both irrigation and domestic use—the third week in July, when people are watering lawns more and taking more cool showers due to the heat.

Brockway said that based on those estimates, a water system for that type of demand would need to be able to draw down 1,090 gallons per minute from the system.

“Not for very long, but it could last several hours during the day,” he said. “This is what you have got to plan for.”

Brockway said the aquifer is more than equipped to provide the 336 acre feet per year that the development would need. He said that number is roughly 0.3 percent of the water that regularly flows through the aquifer—about 40,000 acre feet per year, depending on that year’s snowpack.

The water could be accessed through three wells, he said, but the potential water purveyor would need to ensure that it had the correct water rights and was legally allowed to provide water to the area. 

Brockway said the city of Ketchum could not provide water to McHanville without annexing the entire area, though the Sun Valley Water and Sewer District could either annex the area into the district or contract for services. Mid Valley Water Co. could expand its water rights to include the area as well, he said.

However, the water rights, bought in 2013, would be junior to many in the south valley that are used for agricultural use and date back to the 19th century. Brockway said that while water for domestic purposes would not be shut off in the case of a “call,” a water-saving measure meant to conserve water for senior rights-holders, irrigation water for the developments’ green spaces could be.

“If you have a 2013 municipal water right and a call is made by a senior water user, you won’t die of thirst,” he said. “But your lawn might.”

Kate Wutz:


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