Project Number: 6408-13000-023-21
Project Type: Reimbursable

Start Date: Apr 01, 2011
End Date: Sep 30, 2013

Objective:
The primary objective of this research is to determine optimal application of engineered log jams or other bank-stabilizations measures to minimize associated bed erosion along the Big Sioux River and Skunk Creek, SD.

Approach:
Streambank erosion can be an important contributor of sediment. Bank failures result in channel widening and the loss of adjacent lands. The USDA-ARS National Sedimentation Laboratory (NSL) has determined through an earlier study along the Big Sioux River that various types of bank-stabilization measures would be effective at reducing bank-erosion rates (Bankhead et al., 2010). The Bank-Stability and Toe-Erosion Model (BSTEM) was used to compare erosion rates under existing and mitigated conditions. What is unknown, however, is whether bed erosion (and then further bank erosion) will be initiated as a result of the reduction in sediment supply if successful bank-stabilization measures are undertaken at a large scale along the river. To determine this, a model that not only can dynamically adjust the bed and banks, but also routes flow and sediment needs to be applied. NSL’s channel evolution model CONCEPTS has been used successfully for this type of analysis in various settings across the country. CONCEPTS will be employed along about 100 miles (total) of the Big Sioux River and Skunk Creek to determine the optimal amount of bank stabilization to reduce sediment-loading rates and initiate bed incision. Cross-section data will be surveyed at about 80 cross-sections and combined with field measurements of the resistance of the channel bed and banks to be used as inputs into the CONCEPTS model. A representative flow series of at least 25 years will be used to provide hydraulic input. Simulation runs will be initially conducted for existing conditions and then, the maximum length of bank-stabilization planned/proposed by the state to determine if reductions in bank loads result in bed incision. If de-stabilization of the channel bed is indicated, additional runs will be conducted simulating a reduced length of bank stabilization until an optimal mitigation effort is indicated. The exact types and locations of stabilization measures to be simulated will be determined by NSL and the State. Engineered log jams (ELJs) will certainly be included in the simulation analysis. To support the investigation of performance characteristics of ELJs, physical experiments will be conducted. An existing flume at NSL will be modified to conduct experiments on the hydraulic properties and effects of ELJs on shear-stress distributions and the maximum shear stress that they can withstand. These experiments should help to provide design criteria for these structures. Some of the variables that will be examined include dimensions relative to channel size (height, width), spacing, angle exposed to flow etc. Results of these experiments will then be included in CONCEPTS simulations to determine the optimal conditions for ELJs along the channels.