Erosion-sedimentation in a Closed Drainage Basin in Northwest Indiana1
- L. Darrell Norton2
A closed drainage basin representing a catchment for eroded sediment was studied to determine the amount of erosion since cultivation began, and to determine the spatial relationships of the erosion-sedimentation process that had occurred during 145 yr of agriculture. Post-settlement alluvium (PSA) thickness was easily determined in the field as light-colored mineral soil overlying highly decomposed (sapric) organics in the depression. A detailed field study of the PSA, other geologic sediments, loess, and the original till surface in the watershed demonstrated a reduction in the original relief. The mass of PSA served as a measure of the amount of soil eroded from peripheral slopes. The long term average soil loss was > 26 Mg ha−1 yr−1, which represented an average removal of over 24 cm of soil from the entire watershed in 145 yr. The maximum slope in the watershed was 5%. The loess thickness on the surrounding slopes was used as an indication of the spatial variation of erosion processes. Summit positions and convex slope shapes having divergent runoff had the most erosion while concave shapes with convergent runoff exhibited more sedimentation. These results are essentially opposite to those predicted by the Universal Soil Loss Equation (USLE). Accurate prediction models in the future should consider the dynamic aspects of erosion-sedimentation on landscapes.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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