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Idaho Plans Study Of Building Dam/Reservoir On Weiser River; Cites Salmon Recovery Benefits
Columbia Basin Bulletin August 5, 2011

The Idaho Water Resources Board on July 29 approved the spending of up to $2 million for geologic and operational investigations and analysis that could build momentum toward a long-held goal of boosting water supplies by building a dam in the Weiser River canyon.


“It’s courageous” in a time of considerable state and federal budget austerity, said Jack Peterson, a senior adviser with the Idaho Department of Water Resources.


“And it is very, very forward looking” with population growth and other issues pushing up demand for a limited water supply, Peterson said. And many say climate change – warming -- is advancing and will bring earlier runoff (escapement of water held in mountain snowpack) and drop river flows later in the summer season.


The proposed dam at the Weiser River-Galloway site would hold back nearly one million acre feet of water and inundate 6,918 acres of land. A small irrigation diversion dam has been in place at the proposed site for more than 100 years, Peterson said. The Galloway diversion dam was named after a member of Idaho’s territorial legislature who was an early Weiser area settler.


The site is located 13.5 miles east of the city of Weiser and the Weiser River’s confluence with the Snake River. Wild Snake River steelhead, fall and spring/summer chinook and sockeye salmon are protected by the Endangered Species Act and targets for recovery efforts.


The new dam and reservoir, the planners say, would help boost the region’s power supply, provide flood control and irrigation water, expand recreational opportunities and firm up availability of water for flow augmentation to improve conditions downstream for migrating salmon and steelhead.


“The bottom line is that this project is huge when it comes to salmon recovery in the Columbia River basin,” Peterson said.


The Weiser-Galloway site was first studied after the U.S. Army Corps of Engineers received authorization from the U.S. Senate’s Public Works Committee in 1954. Studies were also advanced in the 1970s and 1980s but the time apparently was not right, Peterson said.


Most recently the Corps, which was hired by the state, completed a comprehensive review of earlier studies, including a rigorous analysis of what gaps in information that would need to be filled before deciding whether to move forward with comprehensive new environmental, engineering and economic feasibility studies.


The Weiser-Galloway Gap analysis, Economic Evaluation and Risk-Based Cost Analysis Project was completed this spring under the Corps’ Planning Assistance to States authority.


Two key issues emerged from the Corps review, the need for: 1) Coring, analyzing, mapping and seismic evaluation of the geologic structure and surrounding faults to determine the safety, suitability and integrity at the dam and reservoir site, and 2) analyzing operational scenarios to confirm and quantify the extent of potential project benefits.


A range of operating scenarios will be analyzed in order to develop a plan that optimizes flood control, hydro, storage, irrigation, recreation and flow augmentation while maximizing economic benefits, according to a fact sheet prepared for the IWRB.


The studies would be conducted jointly by the state and coordinated with the Idaho Power Company, Bureau of Reclamation, Bonneville Power Administration and NOAA Fisheries Service. The studies are scheduled to be completed by mid-2012.


The earth and rock-fill embankment dam itself would be about 300 feet high and 2,200 feet long. Total costs could range up to $500 million (2011 dollars).


Peterson called the estimated $350 to $550 per acre-foot storage capital costs “the most economical large storage project” that could be built.


A new reservoir on the Weiser River would provide economic benefits to the water storage systems on the Boise, Payette and upper Snake rivers through potential substitution and relief of up to 40,000, 160,000 and 200,000 acre feet of water now released respectively from those basins to meet anadromous fish flow augmentation requirements,” the IWRB fact sheet said.


“Flow augmentation benefits for the lower Snake, including reducing Dworshak drawdowns, and firming up availability of water for flow augmentation and fish recovery” is another benefit, the fact sheet says.


Likewise the addition of more on-demand water supply would increase flexibility of flood control rule curves at Brownlee Dam, possibly resulting in additional power generation there, and provide hydropower management benefits for the Hells Canyon Complex and lower Snake/Columbia river hydro systems. Brownlee is one of three Idaho Power Company hydro projects on the lower Snake that make up the Hells Canyon Complex.


Among the board’s charges is to provide financial assistance for water development and conservation projects. The board makes loans and grants from two accounts, water management and revolving development. A third account, the Aquifer Planning and Management Fund, was added by the Idaho Legislature in 2008. That account was established to fund technical studies, facilitation services, hydrologic monitoring, measurement and comprehensive aquifer planning and management.


The 2008 Legislature, in a House Joint Memorial, encouraged the IWRB, in coordination with other public and private entities, to initiate and complete the study of additional water storage projects in the state including, but not limited to, the study of the potential benefits for the Galloway Dam surface water storage project.


The IWRB last Friday authorized its chairman to execute necessary agreements or contracts to carry out the geologic and operational investigations and analysis.

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