基于HEC-RAS的陇南山地山洪灾害风险图优化研究

Optimization study of flash flood risk map based on HEC-RAS in Longnan mountain

短历时山洪是威胁陇南山地交通和村镇安全的重要灾害之一。为提高该地区防灾减灾能力,通过不同雨强计算出洪水淹没损失程度,利用洪水风险区划图指导当地群众预防山洪灾害具有重要的科学意义。基于HEC-RAS水文分析方法,结合GIS软件模拟了流域洪水淹没过程,以陇南山地蒲家沟为研究对象,在5、10、50、100 a一遇设计雨量条件下,综合考虑坡度、土地类型、损失率、水位和流速等多种因素,对传统洪水风险区划图进行优化。结果表明,相比传统方法绘制的风险区划图,优序图法优化后的风险区划图更加重视承灾体的受影响程度,且解决了传统风险区划图中小区域风险等级跨度大,风险等级难以定级的缺点。优化后的风险区划图,上中游无人区风险等级降低,下游人类活动区域风险等级更加明确。以马泉村王家咀为例,在50 a一遇的设计雨量下,传统方法绘制的风险区划图其划分结果涵盖5个风险等级,各区域面积差距不显著,难以确定最终的风险等级。而优序图法优化后的风险区划图划分结果更加集中,王家咀高风险区域面积不足中风险的4%,王家咀风险区域可以明确地定位到中风险。文中优序图法优化后的风险区划图在实用性和适应性上更具优势,可以为小流域山洪预警预报和防灾减灾工作提供帮助。

Short-calendar-time flash flood is one of the serious disasters threatening the safety of transportation of villages and towns in Longnan mountainous area.In order to improve the disaster prevention and mitigation capability of the area,it is of great scientific significance to calculate the degree of flood inundation loss through different rainfall intensities,and to guide the local people in the prevention of flash floods by using the flood risk zoning map.In this paper,based on the HEC-RAS hydrological analysis method,combined with GIS to simulate the flood inundation process of the watershed,and taking Pujiagou in Longnan mountainous area as the research object,the traditional flood risk zoning maps were optimized under the conditions of one-in-5-year,one-in-10-year,one-in-50-year,and one-in-100-year design rainfall,taking into account the multiple factors such as the slope,the land type,the loss rate,the water level,the flow rate,and so on.The results show that compared with the risk zoning map drawn by the traditional method,the optimized risk zoning map by the preferential map method pays more attention to the affected degree of the disaster-bearing body,and solves the shortcomings of the traditional risk zoning map,which is difficult to classify the risk level because of the large span of the risk level of the small areas.In the optimized risk zoning map,the risk level of the upstream and middle reaches of the uninhabited area is reduced,and the risk level of the downstream area of Maquan Village is more clear.Taking Wangjiazui in Maquan Village as an example,under the design rainfall of one-in-50-year,the risk zoning map drawn by the traditional method covers five risk levels,and the area difference of each zone is not significant,which makes it difficult to determine the final risk level.The optimized risk zoning map of the preferred method is more concentrated,and the area of Wangjiazui high-risk area is less than 4%of the medium-risk area,and the risk area of Wangjiazui can be clearly located in the medium-risk area.The optimized risk zoning map of this paper is more advantageous in practicality and adaptability,which can provide help for the early warning and the prediction of flash floods in small watersheds,and are also helpful to disaster prevention and mitigation work.