Evaluation of Effectiveness of Streambank Stabilization Practices and Flood Impact on Cedar River, Nebraska

Stream restoration has been a major environmental objective for preserving biodiversity, reducing loss of valuable cropland and improving water quality. The impact and efficiency of streambank stabilization practices has been simulated using erosion-prediction models; however, evaluation of the erosion-control practices to measure their efficiency is often neglected. This project monitored changes in fluvial geomorphology on the Cedar River in Nebraska and quantified the effectiveness of 18 sites with streambank stabilization practices. A flood event in 2010 due to dam failure acted as a major parameter in measuring the efficiency of the erosion control practices. The methodology included aerial imagery to measure streambank migration over time. Flow data, cross-sectional surveys, radius of curvature of meanders and vegetation density were documented to determine their influence on streambank erosion. Jetties were observed to be the most cost effective under moderate flow conditions, but three out of ten sites failed during the flood event. If the design of the jetties can be modified to provide additional stability without increased costs, the limitation of failures could be reduced. Erosion rates were significantly higher during the flood, especially immediately downstream of the failed dam. While NDVI was an effective tool in quantifying vegetation density and eliminating visual bias, it did not significantly correlate to streambank erosion rates of this river. Additionally, radius of curvature of meander bends did not correlate with erosion rates before or during the flood event. Other factors like local site conditions, root depth and soil type may be more dominant in impacting the streambank in this stream system. Advisor: Aaron R. Mittelste