|Lerch, Robert - Bob|
Submitted to: North American Agroforestry Conference
Publication Type: Proceedings
Publication Acceptance Date: 5/11/2009
Publication Date: 5/31/2009
Citation: Willett, C., Berges, S.A., Lerch, R.N., Schultz, R.C. 2009. Stream Bank Erosion Rates of Small Missouri Streams. North American Agroforestry Conference, May 31-June 3, 2009, Columbia, Missouri. p. 17-26. Interpretive Summary: Contamination of surface waters by sediment remains a major environmental concern in the United States. Soil washed into streams from agricultural lands represents lost productivity and impaired aquatic habitat. Stream banks are a non-point source of sediment that can contribute substantially to in-stream sediment contamination. This study was undertaken to compare the stream bank erosion rates of streams in claypan watersheds that have different adjacent land use. Comparing erosion rates of streams with different adjacent land use is intended to improve strategies for preventing and decreasing stream bank erosion rates and provide the basis for deciding where to place management practices to mitigate stream bank erosion. Study sites were established in the Crooked and Otter Creek watersheds which are located in northeastern Missouri. The land uses studied included forest, pasture with cattle access to the stream, riparian forest, and row-crop. The effect of season on erosion rates was also investigated. Small steel rods installed into eroding banks were used to measure erosion rates. Season was found to be the most important factor affecting stream bank erosion. Erosion rates during the winter were much higher than the erosion rates of any other season. Spring and summer erosion rates were low to moderate, and the fall was marked by low levels of deposition rather than erosion. In seasons where deposition was observed, pasture sites had more deposited sediment than forest and riparian forest sites. In the seasons when net erosion occurred, there were no statistical differences between the erosion rates of the streams with different adjacent land uses. The preliminary results of this study suggest that cattle access to streams caused destabilization of the banks, resulting in bank failure and greater deposition of sediment during low-flow periods. Since seasonal weather effects cannot be controlled, targeting placement of practices that reduce stream bank erosion may best be accomplished by on-site inspection methods to locate eroded stream banks. Analysis of our complete data set to include streams of different sizes may further highlight land-use effects and offer more insights into targeting of practices to mitigate stream bank erosion. The ability to target streams or particular stream reaches that are most erosive will help landowners control stream bank erosion in the most efficient and cost effective way.
Technical Abstract: Sedimentation of surface waters in the United States is a significant environmental concern. Investigating land use impacts on stream bank erosion rates is intended to lead to the development of improved management practices and provide the basis for targeting the placement of management practices to mitigate this problem. The overall objective of this research was to determine the effect of stream order, adjacent land use, and season on stream bank erosion rates. Study sites were established in 2007 and 2008 within Crooked and Otter Creek watersheds, two claypan watersheds located in northeast Missouri. Detailed site information was recorded, including eroded stream bank length, soil descriptions, gullies, debris dams, cattle access areas, and point bars. A factorial experimental design was implemented with four land uses (cropped, forest, pasture, and riparian forest) and three stream orders (1st, 2nd, 3rd). Each treatment was replicated three times for each stream order, except for the cropped 3rd order treatment as only one suitable treatment could be found. Erosion pins were installed based on bank height and length at each site to measure bank erosion/deposition rates. The effect of different seasons was assessed by measuring the length of the exposed pins three times per year (March, July, and November). Statistical analyses were performed to determine the effect of stream order, land use, and season on erosion rates. The results showed that the seasonal effect was highly significant, with much greater erosion rates in the winter of 2008 compared to the other seasons. Land use was significant when low magnitude deposition was observed and was not significant in any of the seasons in which erosion occurred.