Soil Erosion and Sediment Deposition In Granite, Gneiss And Sedimentary Rock Watersheds

Abstract

This study presents results of determination of soil erosion, sediment transport and sediment deposition rates on hill slopes in granite, gneiss and sedimentary rock watersheds in Korea, using traditional on-site methods. Additionally, estimation of erosion rates was conducted with study of the loss of radionuclide 137Cs inventories in tilled soils compared with an initial inventory of radionuclide 137Cs in undisturbed soils. In order to develop an understanding of the medium and short-term intensity and rates of soil erosion by water in the different bedrock watersheds, three methods of erosion measurement were used: (1) natural rainfall plots on hill slopes; (2) sediment traps at the outlets of the watersheds and at the bottom of ponds; and (3) radionuclide 137Cs concentration with depth in the soil profile. This study indicates that soil erosion by water in the watersheds depends on the bedrock types and soil properties associated with hydrological processes. Soil erosion mainly occurs by overland flow in the granite watershed, where soil structures are largely eroded by overland flow, sediments are intensely transported, and rates of soil erosion were estimated to be highest on the shoulder slopes and backslopes. The soil is highly erodible and detachment of soil particles occurs mainly by raindrop impact. Consequently, high levels of sedimentation on the hill slopes and outlets of the watershed showed extreme erosion rates of the soil caused by overland flow during heavy rainfall events. In the gneiss and sedimentary rock watersheds, the soils were primarily eroded by subsurface flows, where limited soil water storage capacity is the dominant reason for generation of saturated flow. However, soils were not strongly vulnerable to erosion by overland flow, i.e., soils were resistant to erosion during heavy rainfalls. Sedimentation in the ponds, the traps and the plots showed low rates of soil erosion there.