Study On Soil Moisture Characteristcs Of Granite Collapsing Hill In Southest Of Hubei

Soil erosion caused by the collapsing hill was very Serious in the Southeast of Hubei Province. Previous studies of the formation mechanism of collapsing hill mostly started from the nature of the soil itself, rarely contained in soil moisture as the research object. In this paper, the objects of study was the experimental plots of the collapsing hill and the non-collapsing hill at Tongcheng in Hubei Province. The soil moisture characteristics of Granite collaspsing hill was analyzed, attributed of measuring the basic properties of soil layers and the soil water distribution after rainfall, by the combination of laboratory experiments and field experiments in Southest of Hubei. Then, the change of soil moisture content over time was simulated by using the Hydrus model at collapsing hill sidewall.The Granite weathering crust has the features of the obvious soil profile level, deep soil and loose parent material. The deposition layer of crust is the most sticky and heavy layer. The order of content of sand (2-0.05mm) in descending is leaching layer (layer A), deposition layer (layer B) and parent material layer (layer C); while the order of content of clay (<0.002mm) is that layer B most and layer C least(only3.80%).The order of the water-released capacity of different layer at collapsing hill sidewall profile follows by layer C, layer A (BC) and layer B. The poor drainage and strong retention abilities of the whole layers are caused by layer B with small ventilation porosity (only1.78%) and large capillary porosity, from the pore distribution. The soil moisture distribution characteristics of sidewall’s profile are that the soil moisture content increasing gradually from the top to bottom of surface soil (layer A), decreasing from the bottom of layer A to layer B and increasing gradually from the bottom of layer B to layer C again. The soil moisture content, with the same depth but different horizontal distance, gradually decreases from inside out at sidewall, further the change gradient of the top profile is more than the bottom.The runoff rises with the increase of rainfall at runoff plots of collapsing hill, in addition that they are both the main driving force for soil erosion. The erosion and runoff were positively related to the rainfall increases, what is said that the increase of rainfall causes runoff generated and carrying sediment increased.The water distribution characteristics of collapsing hill runoff plots are that the change in soil moisture is obviously different from the top of the hill to the bottom, moreover the soil moisture content, in general, gradually increases from the top to the bottom. However, the average gradient of daily change of the bottom is significantly less than the top.The degree of agreement of simulated and measured values is very high in Hydrus model, in addition, the degree of late stage is higher than early stage and the shallow level is higher than deep level, because of the affect of actual environment. Simulating the change of soil moisture content of side wall’s profile, with Hydrus model, is well-operated, as long as inputting accurate parameters. It is significant for the research of soil moisture characteristics at collapsing hill later.