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Flood risk in Treasure Valley of concern

Posted at 5:45 PM, May 18, 2016
and last updated 2016-05-18 19:45:07-04

In the face of ever-growing development in the Treasure Valley, a meeting was held Wednesday to discuss ways to reduce the risk of flooding.

The U.S. Army Corps of Engineers' presentation also factored in ways to increase the area's water supply.

A partnership between the engineers and the Idaho Water Resource Board formed in 2009.

After years of analysis, experts concluded that the best way to both reduce the risk of flooding and increase the water supply is to raise the height of the Arrowrock Dam by 70 feet. 

Concerns over how expanding the dam could change the river hydraulics were included in the analysis. There was talk of raising other bridges to adjust for the new flow, creating a flow split at Eagle Island State Park, which they found would not have created the desired outcome, installing diversions such as inflatable weirs like you see at the Whitewater Park and performing upgrades to head gates. 

It was also mentioned at the meeting that concerns of flooding are growing because the runoff timing is expected to continue to change compared to years past. The board is being told that warmer Springtime weather will melt the snowpack more quickly, with the potential of sending the water downstream all at once.

"Day-after-day goes by and you see increased infrastructure potentially within the flood plain, particularly the 500-year flood plain," said Lt. Col. Timothy Vail, commander of the U.S. Army Corps of Engineers for the Walla Walla District. "We need the public to know the risks associated with flooding in the Treasure Valley, and we need to get everyone's eye on the ball in this regard."

Members of the Idaho Water Resource Board have three options. They could terminate the study, continue on with a new focus or go with a combination of other measures that would still meet the objectives.

The committee members will most likely make their decision by July.

Public comments can be sent to the board chairman.