Author
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Hanson, Gregory |
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Simon, Andrew |
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Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 8/25/1999 Publication Date: 1/1/2001 Citation: Hanson, G.J., Simon, A. 2001. Erodibility of cohesive streambeds in the loess area of the midwestern United States. Hydrological Processes. 15:23-38. Interpretive Summary: In western Iowa alone, time-valued costs associated with channel erosion of 155 streams has been estimated at over $1 billion. Channel erosion consists of detachment of grains or aggregates from the beds and banks of streams. This erosion process results in loss of land, damage to bridges, and ultimately degradation to the environment. Therefore, engineers need field methods to assess erosion resistance of materials in the streambeds and banks to determine appropriate designs for stream restoration and management. A submerged jet apparatus and methodology has been developed to assess the erosion resistance of streambed materials. Field tests were conducted in streambeds in the Midwestern United States. Results indicate that there is a wide variation in the erosion resistance of materials within a streambed, from streambed to streambed, and from region to region. An example of the diversity of materials within a river system is the Yalobusha River system in Mississippi. There are two primary materials within this river system: Naheola and Porters Creek Clay formations. The test results indicate the streambed reaches composed of the Naheola formation are readily erodible over the entire range of flows in the stream system, whereas only the deepest flows generate boundary stresses great enough to erode streambeds composed of the Porters Creek Clay formation. This type of information is essential in determining restoration and management techniques. Technical Abstract: In western Iowa alone, time-valued costs associated with channel erosion of 155 streams has been estimated at over $1 billion. Assessing the erosion resistance of these streambeds is essential in determining appropriate engineering designs for channel restoration and management. Field tests using a submerged jet apparatus were conducted to determine the critical stress and erodibility coefficients for degrading channels in the loess areas of the Midwestern United States. The jet-testing apparatus applies hydraulic stresses to the bed, and the resulting scour due to the impinging jet is related to the excess stress parameters. Streams in which tests were conducted were primarily silt-bedded in texture with low densities, which is typical of loess soils. Results indicate that there is a wide variation in the erosion resistance of streambeds, spanning 6 orders of magnitude for critical stress, and 4 orders of magnitude for erodibility coefficient. The eerosion resistance was observed to vary within a streambed, from streambed to streambed, and from region to region. An example of the diversity of materials within a river system is the Yalobusha River system in Mississippi. The median critical stress value for the two primary materials, Naheola and Porters Creek Clay formation, making up the streambeds was 1.31 Pa and 256 Pa, respectively. Streambeds composed of the Naheola formation are readily eroded over the entire range of shear stress, whereas only the deepest flows generate boundary stresses great enough to erode streambeds composed of the Porters Creek Clay formation. |
