Author(s): Meredith L. Carr; Steven F. Daly; Stephen Hall; Jeremy Giovando
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Abstract: To potentially increase storage over the winter season, the US Army Corps of Engineers has been evaluating flood control operations at Ririe Reservoir near Idaho Falls, Idaho. Because there is little experience with winter releases and a previous winter test release resulted in minor flooding of the Ririe Outlet channel and some surrounding farmlands, it is important to understand the potential problems associated with releases in these conditions. The potential for ice formation and ice jams or snow-slush blockages in the channel downstream of the reservoir were assessed based on simple guidelines, calculations and results of a test release in 2011. Critical flood risk periods were identified, location and rates of ice formation for different antecedent temperature conditions were estimated, and recommendations for measurement for a subsequent release test were proposed. A second Release Test was conducted on 10–13 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. Different behavior in the flowing, though ice-covered, natural channel was observed than in the floodway channel, which was initially empty of water but had restricted conveyance due to snow accumulation. Neither the Initial Release Wave nor the subsequent flow increases 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. The differences in ice formation and snowslush blockage between the Release Test and expected results are discussed.
Year: 2014