BOISE - Water managers are going back to the drawing board in their efforts to reduce flood risks and increase water storage for the Treasure Valley.
In a presentation to the Idaho Water Resources Board, the U.S. Army Corps of Engineers gave an update on a feasibility study focused on raising Arrowrock Dam by as much as 70 feet to create an additional 320,000 acre-feet of water storage capacity in the Boise River reservoir system.
But ultimately, the analysis found that the cost for the project outweighs the potential benefits. Despite the setback, the commander for the Army Corps of Engineers' Walla Walla District says its important to do something to boost flood control in the Boise area.
"The Treasure Valley has the highest flood risk in my entire area of operations that I'm responsible for," said Lt. Col. Timothy Vail. "The Treasure Valley keeps me up at night."
Vail said he is asking for a new three-year timetable and $3 million in funding for a reformulated study of other options.
While potential flooding is the most immediate concern driving the studies, water storage is looming as a near-future problem. Projections show the Treasure Valley's population could more than double to 1.5 million by the year 2065, putting a strain on the area's already stretched water supply.
The 100-year-old Arrowrock Dam was previously identified as one of the most viable options for providing additional water storage and and helping to reduce flood risk.
"We knew it was feasible to raise it," Vail said. "But we still have a large number of unknowns in terms of what kind of construction really is going to be required to make this a safe structure for the next 50 years, to provide benefits for the next 50 years without providing any risk to the community."
Another potential study would look at the possibility of raising the height of Anderson Ranch Dam in the South Fork of the Boise River drainage to provide more water supply for the Treasure Valley and surrounding communities, such as Elmore County.