[HCG23-P04] Effects of soil moisture variation on rainfall infiltration and erosion of the badland soil in Taiwan
キーワード：mudstone , rainfall erosion, artificial rainfall experiments, infiltration
The mudstone area in southwestern Taiwan has poor geological conditions, severe erosion and poor vegetation. This area, recognized as the badland, is the most difficult area for remediation and revegetation after hillslope disasters. Widely distributed in southwestern Taiwan, the mudstone is known by its poor water permeability. The mudstone is softened with water, but hardens and cracks without water. In this study, we collected the mudstone deposits in the Agongdian Reservoir area, and used them as the soil specimens for investigating the soil erosion processes in the cases of different slope gradients and precipitations. Two major sets of experiments were carried out in this study. The first set of experiments aims to observe the characteristics of soil shrinkage and expansion under different soil moisture conditions. We measured the soil volume at different moisture contents, and estimated the porosity and infiltration rate, in order to obtain the soil characteristic curve values. In the second set of experiments, we applied the artificial rainfall experiments on the soil specimens, which was filled in a glass erosion planform with the dimension of 25 cm, 15 cm, and 75 cm, in width, depth, and length, respectively. Two rainfall intensities (75mm / hr, 100mm / hr) and seven slope gradients (0 °, 5 °, 10 °, 15 °, 20 °, 25 °, 30 °) were assigned in the 30-minute simulated rainfall events. During each trial of the simulated rainfall experiments, surface runoff, infiltration, and outflow sediments were collected for every five minutes. Meanwhile, the soil moisture content and erosion topography were monitored by using a soil hygrometer (TDT) and a digital camera. Results from the experiments are analyzed and discussed, in order to propose the inter-relationships among soil moisture content, porosity, infiltration, and runoff erosion. Consequently, the outcome of this study may provide references for the assessments of hillslope erosion and disaster evaluation of the badland in Taiwan.