Geological hazard risk assessment and suggestions for risk control in Chaya County, eastern Tibet

Chaya County Town in eastern Tibet was selected as the research area for the susceptibility assessment of geological disasters. Seven evaluation indexes, including elevation, slope grade, slope form, slope direction, slope structure, stratum, and distance from fault, were selected to construct an evaluation model of geological disaster susceptibility using the evidence weight method. Using the annual maximum daily rainfall under four rainfall frequencies (10%, 5%, 2%, 1%) as the dynamic inducing factor and building population and transportation facilities as the hazard bearing body, the dynamic risk of geological hazards in the town was evaluated. The results show that except for the slopes on both sides of the county town, which were mainly high-risk and extremely high-risk areas, other areas in the research area were mainly medium and low-risk areas. As the frequency of rainfall decreased, the areas of high-risk and extremely high-risk areas increased by a maximum of 25.81% and 0.44%, respectively, while the areas of low-risk and medium-risk areas decreased by a maximum of 20.03% and 6.52%, respectively. Based on the risk assessment results, a method for controlling the source of geological hazard risk considering different rainfall frequencies was proposed. Specifically, for the extremely high-risk areas under the four rainfall frequencies of 10%, 5%, 2% and 1%, it is recommended to adopt engineering management, engineering management/professional monitoring, professional monitoring, and professional monitoring/combination of mass monitoring and professional monitoring. For the high-risk and medium-risk areas under a 1% rainfall frequency, the recommended risk control measures were the combination of mass monitoring and professional monitoring, and the combination of mass supervision and mass prevention.The risk management and control system accounted for the dynamic risks of slopes under different rainfall frequencies, which would enhance the management and control of geological hazard risks in mountainous urban areas in a refined manner.