Water Resources Research Act Program

Details for Project ID 2012NE234B

Direct Monitoring of Knickpoint Progression

Institute: Nebraska
Year Established: 2012 Start Date: 2012-03-01 End Date: 2013-11-30
Total Federal Funds: $23,238 Total Non-Federal Funds: $46,566

Principal Investigators: David Admiraal, David Admiraal

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.