Geo-Informatics in Resource Management and Sustainable Ecosystem

Soil moisture is one of the key hydro reasons that caused the debris flow. In this paper, a simulation model, based on the physical process of hydro cycle and the distributed hydrology model: TOPMODEL,is built to simulate the soil moisture variation in Jiangjia ravine in 2001. In this model, the potential evapotranspiration is computed with the Penman-Monteith equation; the water movement in the unsaturated layer of the soil is described by the one dimension Richards equation and the saturated base flow is based on the principles of the TOPMODEL and the surface runoff is calculated by an experience equation. The soil column is divided into 5 layers and we calculate the water balance for each layer. Background data, include vegetation, soil texture and micrometeorology, are come from the interpretation of the Quick Bird image and the field surveying. The cell size of Dem data, with the scale of the 1:100,000, is 50m×50m. Compared the simulation result with the field data which is got by the oven-dried way from 20 June to 7 July and the 17 debris flow events of the 2001, we have some conclusions: 1) The simulated data has the same variation trend with the field data with the same magnitude during surveying time; 2) The history precipitation was accumulated in the soil near the land surface; 3) The average basin’s saturation degree (ABSD) may be a quite good index to evaluate the soil water conditions and the value of the 70% of the ABSD is the critical soil water condition of the initiation of the debris flow; 4) When the soil is wetted enough(ABSD>=70%), the debris flow in Jiangjia Ravine can be easy trigged by the precipitation of bigger than 25 mm per day or by the precipitation between 5 mm to 25 mm with short time heavy rainfall which can generate more than 0.35 m/s unit discharge. The model built in this paper provides a physical basis for the understanding of the debris flow initiation conditions of Jiangjia Ravine.