Studies On Mountain Flood Disaster's Early-warning Index In Small Watershed Of Ji'an City

Ji'an City is located in the southeast of Jilin Province.It is a typical hilly area and a region with severe mountain flood disaster and a large number of threatened populations.Based on basic data,basic information of small watersheds,river surveys and hydrometeorology,this paper took 117 typical small watersheds in Ji'an city as research objects,and used Arcgis,HEC-RAS and other softwares to perform flood calculations and analysis.Analyzed the current flood prevention capacity of the villages along the river,carried out the classification of flood danger zones and statistical analysis of population and houses in dangerous zones at various levels,comprehensively determined the critical rainfall and drew a map of the danger zone to provide support for the flood disaster prevention plan,transfer people,and temporarily resettle,etc.The main contents and conclusions are as follows:(1)Early warning index analysis system: According to the collected basic data,it was evaluated from the aspects of availability,reliability,completeness,consistency,etc.The evaluation showed that the basic data met the needs of early warning index analysis.According to the rainfall division and small watershed characteristics of Ji'an City in Jilin Province,the early warning index analysis system suitable for Ji'an city was determined,that was,the design flood part adopted the inference formula method,and the early-warning indicator analysis used the distributed basin hydrological model method with physical mechanism.(2)Current flood prevention capacity: Based on the design flood,an analysis of the current flood prevention capacity of 117 villages along the river was carried out.In the 117 riverside villages,the analysis showed that the current flood prevention capacity of 22 riverside villages was very high,the probability of being affected by the torrential rain and flood disaster of river was not high;There were 0 villages with current flood prevention capacity less than once in a year;59 villages once in 1 to 5 years;22 villages once in 5 to 20 years;14 villages once in 20 to 100 years.Based on the analysis of the current flood prevention capacity,the population numbers and distribution of 95 dangerous areas along the river in the villages affected by the torrential rain and flash flood disasters in Ji'an City were counted.The analysis showed that of the 95 villages along the river,the total population threatened was 3789,of which 1,050 were in extremely high-risk areas;1,675 were in high-risk areas;and 1,064 were in dangerous areas.(3)Early warning index: Based on the analysis of the current flood control capacity,an analysis of early warning indicators was conducted for 95 villages along the river whose current flood control capacity was less than a century.Because the water level early warning index does not meet the requirements for implementation,this paper does not recommend the use.The early-warning index of rainfall was determined by critical rainfall,which was divided into two periods of one hour and three hours.The two levels were ready to transfer and immediate transfer.Finally,the early-warning indexes of 95 villages along the river were determined comprehensively,and then the early-warning indexes of 10 towns were determined,and the isoline map of early-warning rainfall was drawn.