Efficacy of rainfall-induced landscape degradation on soil-mantled hillslopes

Authors: Sean J. Bennett*, University at Buffalo, Henrique G. Momm, Middle Tennessee State University, Robert R. Wells, U.S Department of Agriculture-Agricultural Research Service
Topics: Geomorphology, Earth Science
Keywords: soil erosion, landscape degradation, hillslope geomorphology
Session Type: Paper
Day: 4/12/2018
Start / End Time: 3:20 PM / 5:00 PM
Room: Balcony K, Marriott, River Tower Elevators, 4th Floor
Presentation File: No File Uploaded

Soil-mantled hillslopes subjected to exogenic forcing by rainfall will create discrete erosion regimes that include rain splash, sheet flow, rills, and gullies. While these erosion processes can cause significant soil and landscape degradation, rills and gullies tend to attract mitigation efforts by farming communities, assuming that such erosional channels contribute more to these degradation indices. This study seeks to determine the relative efficacy of rainfall-induced landscape degradation as compared to overland-flow induced erosion, where the amount of water exiting the hillslope is the same for both regimes. An experimental landscape was filled with silty loam soil and subjected to simulated rainfall and base level adjustments to force landscape evolution. Once the landscape reached a steady-state condition, the applied rainfall was stopped and replaced by an equivalent rate of overland flow. The results show that the rainfall regime proceed 20 times more sediment efflux from the landscape as compared to the overland flow regime. More importantly, the sediment discharge from the rainfall regime was enriched in silt and clay and depleted in sand, whereas the sediment derived from the overland flow regime was enriched in sand and depleted in silt and clay. These results clearly demonstrate that the rainfall-induced forcing produced more landscape degradation than an equivalent overland flow. For effective management, emphasis should be placed on protecting soil surfaces from raindrop impact and sheet flow, give that these processes may produce more landscape degradation as compared to rill and gully erosion.

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