To potentially increase storage over the winter season, the US Army Corps of Engineers Walla Walla District is currently evaluating flood control operations at Ririe Reservoir. Because there is little experience with winter releases and a previous winter release resulted in minor flooding, it is important to understand the potential problems associated with releases in these conditions. Therefore, the Corps conducted a Release Test on 1013 February 2013. Throughout the test, instruments took detailed measurements of the water temperature, stage, and discharge along the Willow Creek channel; and personnel observed the dynamic ice conditions.
Two members of the Ice Engineering Group at CRREL participated in the test release from Ririe Reservoir, located near Idaho Falls, ID from 812 February 2013. Personnel from the Corps Walla Walla District, the Bureau of Reclamation, USGS, State of Idaho, and local irrigation districts also participated. The release was conducted in frigid weather to test the feasibility of modifying the current winter time operations of the reservoir. The release was through 15 miles of the undeveloped Willow Creek and then through 7.7 miles of the normally dry overflow channel to the Snake River. Prior to the release, CRREL personnel worked with the Walla Walla to characterize the snow conditions in the overflow channel and the ice conditions in Willow Creek. The release commenced at 1400 on Sunday, 10 February, with an initial release of 150 cfs and was increased in a series of steps to a maximum of 500 cfs that was held for 24 hours. The flow, depth, water temperature, and meteorological data that were collected during the test release were analyzed and results are detailed in ERDC\CRREL TR-13-10, Ririe Dan Release Test Asssessment.
The test included an initial release of 150 cfs for 28 hr; a rapid increase to 300 cfs, which was held for 14.5 hr; and another rapid increase to 500 cfs, which was held for 24 hr. The flow was then shut off. Neither the Initial Release Wave nor subsequent flow significantly removed, dislodged, or eroded snow in the channel; the snow melted only after a thermal melt-out front advanced downstream. No out-of-bank flooding occurred. As a result of the information gathered from this Release Test and from one in 2011, this report presents a series of recommendations for future wintertime releases.