RISK EVALUATION OF AVALANCHE, LANDSLIDE AND MUDFLOW HAZARDS IN THE UPPER REACHES OF THE YELLOW RIVER

Based on field geological investigations of avalanches,landslides and mudflows in the upper reaches of the Yellow River,the authors determined the main influence factors and index system of the hazard risk evaluation and made risk evaluation with the county(city or qi) as a unit.There are a total of 116 units in the study region and the geological hazard risk is divided into 5 grades.There are 3 high risk units,8 relatively high risk units,24 moderate risk units is three,54 relatively low risk units and 27 low risk units.The results of risk evaluation indicate that the risk grades of avalanche,landslide and mudflow hazards differ greatly in different area of the region.The general distribution pattern is as follows:the risk is higher in the central area and lower in the north and south.The risk indices show that the risk indices of some risk units are very close to the critical value,and once the dangerous conditions and vulnerable conditions change,the risk grades of geological hazards would change accordingly.Therefore during the development of western China,whether for mineral exploration and mining or for various engineering operations,we should pay attention to environmental protection so as to avoid aggravation of geological hazards.