| The area in mountain was caused tens of thousands of collapse, landslides, lakes, debris flow and other secondary geological disasters after"5.12"Wenchuan earthquake, and there were more than one hundred of debris flow in Wenchuan County alone, which widely distributed types of complexity, huge breakage, and brought serious safety problems for setting the residents of settlements, restoration and urban planning. Once the outbreak of debris flow, it will result in heavy casuaoties and economic loss, which would endanger the lives and property and the people seriously. Therefore, take research assessment, disaster nitigation, early warning and forecasting for debris flow in mountain is particularly important.The evaluation of the risk of debris flow is based on many different triggers of landslides, then establishes evaluation index system and evaluation model with the help of spatial analysis in the GIS software, resulting in risk assessment map currently. But most of these based on grid cell, which have certain defects in accurate expressing the real situations. The author investigates and analyzes the factors in differet scales, including the drainage area, the relative height difference, the cumulative amount of convergence, slope, regional tectonic acticity, land use and human activities based on DEM and remote sensing data, mainly in the vector data, raster data supplemented. Finally, according to debris flow hazard assessment model, the suthor divides Wenchuan County of Minjiang River into five danger levels of debris flow, and the conclusions as following:(1)The study area is divided into two different scales basin and watershed is extracted from their information used DEM as the primary data source. When the threshold of catchment is 100,000, the study area is divided into 209 sub-basin. When the threshold of catchment is 500,000, the study area is divided into 40 sub-basin.(2)Geomorphic information entropy can reflect the strong degree of the late Quaternary uplift, which shows the intensity of tectonic activities, so geomorphic information entropy is used here instead of the calculation of the regional tectonic activity. The results show that most of Wenchuan area landscape evolution in the prime of life, the general strength of the regional tectonic activity. Landslides in the area has a variety of dynamic conditions, due to the erosion of river basin and regional tectonic activity intensity in the upper reaches of Minjiang River County high frequency of debris flow activity.(3)The debris flow is done hazard assessment based on two watershed scales, and the study area is divided into five ranges from high to low. There are 33 highest risk of debris flow basins, 52 higher risk of debris flow basin, 54 middle basin debris flow risk, 48 lower risk of debris flow basin, 22 basins with low risk when the threshold of catchment is 100,000. At the same time, there are 5 highest risk of debris flow basins, 10 higher risk of debris flow basin, 10 diddle basin debris flow risk, 9 lower risk of debris flow basin, 6 basins with low risk when the threshold of catchment is 500,000.(4)The divided results show that: the Minjiang River is a high risk area of debris flow activity because of expansion of the water branch, and a strong regional tectonic activity. Near the Minjiang River, and Mao county and S303 road are high debris flow hazard because of the valley development and loose solid material gathered fast. The northwest, central and eastern areas of Wenchuan, debris flow activity is the middle frenquency. Good vegetation covers southwestern region, slope deposits and riverdeposits together into a low debris flow risk. Wenchuan southwest is higher region, the trench stability, watershed is low, the possibility of occurrence of debris flow is lowest. |
