Tim Page: Boise River dams built for irrigation, not flood control


February 23, 2014 

A Feb. 2 story in the Idaho Statesman concerning the water challenges we face in the Treasure Valley contained a sub headline — “The Boise River’s three-dam system was built for flood control, but Otter wants to expand it for irrigation” — that was inaccurate. In fact, Arrowrock and Anderson Ranch dams were both built for irrigation and Lucky Peak was built in 1955 for flood control due to the massive flood of 1943. The Idaho Supreme Court has recognized that the primary purpose of Arrowrock and Anderson Ranch was to capture flood waters and make them available for irrigation and the court has confirmed that the water stored behind those dams are held for the purpose of irrigation. This is a critical fact that is missing from the article.

A series of articles from the Idaho Daily Statesman historical archives from 1913 to 1920 revealed that the Statesman reported that Arrowrock Dam was built for reclamation purposes. None of these articles listed flood hazard or flood control as a motivating factor behind the dam.

In a 1914 article, the Statesman reported that the Reclamation Service was hurrying the completion of the dam so that it could furnish water for irrigation during the 1916 growing season. The dam was planned shortly after the Reclamation Act passed in 1902, offering Boise farmer’s “irrigation insurance.”

By the late 1930s, the Boise Valley needed more water for irrigation and electricity. Anderson Ranch was approved in 1940 and became operational in 1950. While flood control was also needed this was not the commissioned purpose of the Anderson Ranch. In the 1950s when Congress decided to build Lucky Peak for flood control, the United States and the irrigation districts agreed that the reservoirs could be operated by the United States for flood control, but not at the expense of irrigation storage.

The purpose of this historical exercise is to put Boise River water use into perspective. The Treasure Valley became the Treasure Valley due to the irrigation water supplied by Arrowrock and Anderson Ranch dams. Over 200,000 acres of land depend on that irrigation storage. Flood control, recreation, enhancing fish and wildlife and many other ancillary benefits come from the operations of the reservoirs.

Flood control sounds like it is the most important part of the Boise Project because of the encroachment of development along the stream banks of the Boise River.

Millions of dollars of homes and businesses have been built right up to the current flood stage of the Boise River, which is set at 6,500 cubic feet per second. Many of these homes and businesses would have already been washed downstream or damaged beyond repair if the U. S. Army Corps of Engineers in cooperation with the Boise Project had not been releasing water from storage to make room for higher runoffs.

The Boise Project supports the governor’s efforts to study the flood control, irrigation and other demands for use of waters from the Boise River. This Valley is faced with significant development pressures that will require both water supply and flood control. It is prudent to plan for the future.

However, in considering these studies the public should not be left with the mistaken impression that the Boise River reservoirs are entirely devoted to flood control and that irrigation is something that the governor wants to add on to the system.

Tim Page is the project manager for Boise Project Board of Control.

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