Comments Sought On Raising Arrowrock Dam 

Pretty dam high

A conversation about raising Arrowrock Dam that began in 2007 continues with a public comment period ending on Monday, June 23. The dam was the tallest in the world when it was built in 1915, at 350 feet. Now, the U.S. Army Corps of Engineers is considering raising it another 70 feet, which would double the reservoir's capacity and reduce flood risk. The price tag is estimated around $1 billion for the project.

One purpose of the projected expansion would be to keep up with water demands in the Treasure Valley, with the capability to handle drought years like this one.

But "building a big slab of concrete doesn't mean the water will come," said Idaho Rivers United's Boise River Campaign Coordinator Liz Paul. She said her organization isn't thrilled about the project.

She said better water security could come from smarter irrigation methods, like drip irrigation and leak repairs. She also advocates for flood management, rather than reduction. She applauds city efforts that allow the river to make natural fluctuations, like the Marianne Williams Park in Barber Valley. The park is built to accommodate the floodplain, just as the proposed Esther Simplot Park off Whitewater Boulevard will do.

The dam's expansion could also impact the south and middle forks of the Boise River, which the Idaho Conservation League says will inundate seven miles of the river upstream and ruin habitat of endangered bull trout. Those areas are currently popular for angling, camping, hiking, floating and big game hunting.

The Corps is viewing the Boise River downstream of the Lucky Peak dam as an "area of potential effect." Paul said raising Arrowrock Dam would put less water in the Boise River.

"So you build a multi-million dollar whitewater park and you get no water flowing through it," Paul said. "You get dead cottonwood and poison ivy everywhere."

She said that could impact riparian areas and fish habitat, boost algae growth and fail to dilute wastewater poured into the river.

The Corps has teamed up with the Idaho Water Resource Board to conduct environmental impact studies on the dam expansion. They extended their public comment period another month, ending on Monday. They want comments regarding the scope of issues and alternatives, including how this might affect commuting along the Boise Greenbelt, or how water rates could change.

A decision on whether or not to proceed with the expansion of Arrowrock Dam is expected in the next 18 months.

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