Solutions Workshop Sparks Ideas for Sediment Management at the Lewis and Clark Lake Region

YANKTON, SD – Five sediment management experts came to the Lewis and Clark Lake region to participate in a Solutions Workshop to consider ideas for sediment management. The workshop is part of Phase 2 of the Planning Assistance to States Study – Lewis and Clark Sediment Management Plan. The study is funded 50-50 between the US Army Corps of Engineers and MSAC and its stakeholders. MSAC requested the USACE for this technical assistance.

The first day of the workshop, June 15, 2021, the five experts viewed the sediment delta and Niobrara River and Ponca Creek tributaries with USACE staff and MSAC representatives. The second day, the experts joined Corps staff, MSAC representatives along with state and tribal stakeholders in a small workshop to freely discuss sediment management ideas which totaled more than 20. After discussion and deliberation, four ideas were selected and presented to the public during an open house the following day.

The four ideas included watershed sediment management, dredging, sediment trap and truck, and sluicing. Here you will see a compilation of several of the ideas along with an introduction by Rollin Hotchkiss and a historical overview provided by Paul Boyd, hydraulic engineer with US Army Corps of Engineers – Omaha District.
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A closer look …

Sediment Trap and Truck refers to strategic placement of sediment retention structures on tributaries.  Operation and maintenance of this system would be a concern as the structures might be filled relatively soon and require material removal. It makes sediment more accessible for moving but still requires the handling and placement of the material. John Shelley, a hydraulic/sedimentation engineer at the USACE-Kansas City District, discusses sediment trap and truck.

Watershed sediment management would work to compliment most any sediment management strategy. The aim is to reduce sediment inflow into Lewis and Clark Lake. Actions could include streambank stabilization, gully stabilization, grade control, farm ponds and upland soil conservation practices such as buffer strips and cover crops. This is not a stand-alone solution but could be part of a big picture solution, which study partners are working to do with a sediment management plan for the region. Meg Jonas, retired US Army Corps of Engineers – hydraulic engineer, discusses watershed sediment management.

Sluicing was another general idea presented at the open house. Sluicing could potentially export large volumes of sand downstream and go a long way toward achieving sediment balance. It is relatively inexpensive. Some disadvantages of the reservoir drawdown required for sluicing on a regular basis include that it would decimate fish stocks in the lake and there could be hydropower impacts such as modification of power intake to exclude sediment and a reduction in hydropower production. Greg Morris, P.E. Ph.D., has 45 years of professional engineering experience internationally and outlines sluicing.

Dredging is a traditional way of moving and removing sediment. Ideas presented focused on the unvegetated frontal face of the delta, closest to the open lake. As the five contributors found during a boat tour on Tuesday, the front of the delta extends a significant distance into the lake under the water’s surface. This is not a new revelation, but this location was discussed in detail as it is the closest to the dam, and the system’s ability to move sediment downstream. As part of Phase 2, three dredging scenarios will be analyzed using the traditional economic model and the life-cycle model which considers a bigger picture. Dredging is typically viewed as a high cost alternative to attempt to keep up with the annual inflow of sediment. It could also be implemented at specific locations for infrastructure needs.

View the Stakeholder Update which was held August 16, 2021

August 16, 2021 Stakeholder Update Meeting in Yankton

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