Results from the Phase I Lewis and Clark Lake Sedimentation Management Study indicate that high discharge, short duration reservoir releases out of Fort Randall Dam could help transport significant amounts of fine sediment out of the Missouri River.
The build-up of silt and sand behind Gavins Point Dam has been an area of concern for the Corps since the dam was constructed during the 1950s. In the release of its 2003 Amended Missouri River Biological Opinion, the U.S. Fish and Wildlife Service recommended the Corps study the feasibility of using hydraulic flushing to provide sand for shorebird habitat below Gavins Point Dam to aid in habitat development in the lower reaches of the Missouri River.
Phase I examined whether flushing could help restore the balance of sediment and sand in the lake and the Missouri River reach below Gavins Point Dam.
“What we learned is that a high discharge, short duration flush would not likely meet the goals of providing sand for shorebird habitat below Gavins Point dam, ” said Paul Boyd, a hydraulic engineer in the Corps’ Omaha office . “ However, when we modeled lowering the spillway gates, the results showed higher sediment transport. Lower flows for longer durations possibly in conjunction with modifications to the dam structure may yet provide us with a feasible sediment management solution .”
The Corps is currently evaluating the potential for combining the modification of structures with flows in Phase II of its study. During the modeling design and analysis, Corps staff and basin stakeholders identified other combinations of flow, timing, and infrastructure modifications that may produce more effective sand transport to the downstream channel. The Corps initiated a Phase II/follow-up study in late 2012. The second phase is expected to be completed by the end of 2013.
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Press Release, May 24, 2013