State Water Resources Research Institute Program


Project ID: 2012NE234B
Title: Direct Monitoring of Knickpoint Progression
Project Type: Research
Start Date: 3/ 1/2012
End Date: 2/28/2013
Congressional District: 1
Focus Categories: Geomorphological Processes, Sediments, Water Quality
Keywords: Knickpoint, Erosion, Bed Stabilization, Sediment
Principal Investigators: Admiraal, David Mark (University of Nebraska - Lincoln); Admiraal, David Mark (University of Nebraska - Lincoln)
Federal Funds: $ 11,619
Non-Federal Matching Funds: $ 23,283
Abstract: Over the last century, channel erosion in the Midwest has greatly accelerated due to the straightening of stream corridors composed of highly erodible soils. When a stream is straightened, the slope of the stream is artificially increased. In the Midwest, where coarse bed materials are uncommon, the increase in slope is usually balanced by an increase in bed and/or bank erosion. The problem of bed erosion is prevalent in Nebraska because most streams have a bed layer with an erodibility that is only moderately less than the erodibility of the soils that make up the sub-soils below the bed layer. Slight increases in channel slope can form enough excess energy in the flow to break through the bed layer into the more erodible sub-soils, and a perturbation point that undermines the bed layer forms. This perturbation point, called a knickpoint, migrates upstream as it undermines the stream bed, leaving a deep, incised channel in its wake. Many streams in eastern Nebraska are particularly susceptible to bed and bank erosion problems related to knickpoints (Rus et al., 2003). Recent research also indicates that bank erosion is a significant contributor to Phosphorous yields in the Missouri River Basin (Brown et al., 2011). The goal of the proposed research is to conduct a field investigation of the geometry and hydraulics associated with knickpoint migration in midwestern streams to better understand how to stabilize the streams and reduce unnatural bank erosion. Continuous monitoring of knickpoint geometry and hydraulics is proposed to determine under what conditions the knickpoint will fail and migrate. Time lapse images in combination with Particle Image Velocimetry will be used to monitor knickpoint migration and related water velocity distributions, respectively. The study will help to predict knickpoint point migration and subsequent stream bank erosion more accurately. In addition, better knowledge of knickpoints will allow more cost efficient grade control structures (e.g., sheet-pile weirs and flumes) to be identified to control knickpoint propagation and reduce bed and bank erosion.

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