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|Freezeup dynamics of a frazil ice screen
|United States. Army. Office of the Chief of Engineers
Axelson, Kathleen D.
Frazil ice control structures
|Cold Regions Research and Engineering Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
|Special report (Cold Regions Research and Engineering Laboratory (U.S.)) ; 90-4.
Abstract: Fence booms made of wire mesh screen have been proposed as economical, temporary frazil ice control structures. These screens incorporate frazil ice as it freezes to the screen material. eventually forming a frazil ice dam and raising the water level at a specified location. The purpose of raising the water level is to allow the formation of a stable ice cover that will incorporate still more frazil ice through hydraulic thickening of the cover and deposition beneath the cover. A series of experiments examining the freezeup and blocking dynamics of an expanded metal frazil ice screen were conducted using both an impermeable barrier and frazil ice. A qualitative analysis of the complex frazil ice accumulation process indicated three phases of blocking-an orifice flow stage, a transition stage, and a permeable flow stage. A fourth phase, weir flow, was observed in some cases, and is expected to occur in prototype structures. High downstream flow velocities were associated with the orifice and transition stages. Downstream velocities decreased during the permeable flow stage, although piping resulted in velocity jets. The test results indicate that a rapidly and completely blocked screen is desirable to minimize the time during which high downstream velocities, which lead to bed scour, occur.
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