月度防控视角下韩江下游城镇地质灾害危险性评价

Risk assessment on geological hazards in urban areas of lower reaches of Hanjiang River from perspective of monthly prevention and control

华南山区地质环境条件复杂,地质灾害频发,亟需开展区域地质灾害危险性评价,解决“地质灾害最可能发生月度及相应易发区在哪里”的问题,以针对性地分级、分阶段部署相应防控措施,有效降低地质灾害可能造成的损失。以韩江下游广东省梅州市留隍镇为例,选取坡度、坡形、高程、工程地质岩组、土层厚度、距断裂距离、植被NDVI值与用地类型共8个评价指标,通过灾害频率比(FR)模型对指标分级赋值;采用灰色关联度法计算指标权重,结合信息量模型完成研究区地质灾害易发性评价,并通过ROC曲线对结果进行验证;在易发性评价的基础上,将月度作为最小时间评价尺度,以历史发灾记录最大月均降雨量作为激发极值优化降雨假设模型,计算1~12月地质灾害发生概率,并完成各月度地质灾害危险性评价及分区。结果表明:①总体上,留隍镇地质灾害共划分为低易发区、中易发区、高易发区、极高易发区4类易发区,各区面积占比分别为58.60%,22.99%,13.39%,5.02%,经ROC曲线检验评价精度达到0.81,表明评价结果客观有效。②月度地质灾害危险性评价结果显示,5~8月留隍镇地质灾害发生概率最大,建议将其作为全年重点防御时段;且集中分布于留隍镇北部、中部及南部,建议将上述区域作为重点防御区。研究成果可为研究区域年内不同月度地灾防控工作安排及防控措施动态调整提供参考。

The geological environment conditions in the mountainous areas of South China are complex,and geological disasters occur frequently.It is urgent to carry out regional geological hazard risk assessment and solve the problem of“where geological disasters are most likely to occur on a monthly basis and corresponding high-risk areas”,and deploy corresponding prevention and control measures in a targeted and phased manner to effectively reduce the losses.Liuhuang Town,Meizhou City,Guangdong Province,located downstream of the Hanjianh River,was selected as the research area.Eight evaluation indicators were selected,including slope gradient,slope shape,elevation,engineering geological rock group,soil thickness,distance from the fault,vegetation NDVI value,and land type.The indicators were graded and assigned values using the disaster frequency ratio(FR)model,and the weight of indicators was calculated by the grey correlation method.The geological hazard susceptibility in the study area was evaluated with an information quantity model,and the results were verified through ROC curves.Based on the susceptibility evaluation,a month was used as the minimum time evaluation scale,and the maximum monthly average rainfall in historical disaster records was used as the excitation extremum to optimize the rainfall assumption model.The occurrence probability of geological hazards from January to December was calculated,and the risk assessment and zoning of geological hazards in each month were completed.The results showed that:①Overall,the geological hazards in Liuhuang Town were divided into four types of prone areas,namely low prone area,medium prone area,high prone area,and extremely high prone area.The area proportions of each area were 58.60%,22.99%,13.39%,and 5.02%,respectively.The accuracy of the ROC curve test evaluation reached 0.81,indicating that the evaluation results were objective and effective.②The monthly geological hazard assessment results showed the probability of geological disasters occurring in Liuhuang Town was the highest from May to August.This period was recommended to be a key defense period for the whole year.Spatially the disasters were concentrated in the northern,central,and southern parts of Liuhuang Town,which should be assigned as key defense areas.The research results can provide a reference for the dynamic adjustment of disaster prevention and control work arrangements and measures in different months in the research area.