Study On Risk Assessment Method Of Mountain Torrent Disaster In Small Watershed Of East Yunnan Province

The paper starts from the current situation of prevention of mountain torrent disasters in Yunnan.It summarizes the research development of risk evaluation of mountainous watershed flood.Based on characteristics of the small watershed in the eastern regions of Yunnan province,this paper compares classic risk evaluation of mountainous watershed flood.It raises a new one which takes an example of small watershed in Banqiao of Luoping county.The paper makes an empirical research of risk evaluation of mountainous watershed flood in the eastern regions of Yunnan province.The conclusions as following:(1)It analyzes characteristics of the small watershed in the eastern regions of Yunnan province.Because of the special geographic position in Yunnan province and the unique geographic and geomorphic conditions in the eastern regions of Yunnan province,the eastern regions of Yunnan province is one of the rainstorm centers of Yunnan.The average precipitation for many years exceeds 1600 m.The average annual rainstorm days in Luoping county is more than 3 days,some years even reach 5.4 days and the frequency is high.The small watershed bursts and harms strongly and frequent.In the meantime,the flood-control capacity is low in the eastern regions of Yunnan province because of the general capacity is low.(2)It raises a kind of risk assessment method that is suitable for mountain torrent disasters in the small watershed of the eastern regions of Yunnan province.At first,it uses the experience formula method to design the rainstorm and runoff producing calculation,and uses the comprehensive instantaneous unit line to analyze the converge and calculate the flood process.By this way,it not only can make full use of this two methods,but also can get a better risk assessment that is suitable for actual conditions.Next it uses manning formula to derive the design flood level.Then it analyzes the inundated areas based on DEM system.At last,it adds up the distribution of population and construction in different danger zones according to the submerged areas,so it can evaluate the flood disaster losses.(3)The risk assessment of mountain torrent disasters of the typically small watershed in Banqiao town Luoping County has been done.Taking this small watershed in the eastern Yunnan Province as an example,the risk assessment of mountain torrent disasters method,which is based on the storm flood count and the Digital Elevation Model,has been applied in.According to the calculation of storm and flood in small watershed,the designed peak flood flow of 10 important reaches control section in Banqiao watershed had been calculated by the hydrological analogy method first,then the flood flow level was calculated by the manning formula.And the results are as follows: the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Duoyishu village respectively is 1433.47 m,1433.04 m,1432.31 m,1431.83 m,1431.26m;the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Jiangtiansuo village respectively is 1416.42 m,1415.82 m,1414.79 m,1414.12 m,1413.30m;the designed peak flood flow level of p=1%、p=2%、p=5%、p=10%、p=20% of the control section in Caiyuan Group3 respectively is 1417.20 m,1416.28 m,1414.71 m,1413.70 m,1412.48m;the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Caiyuan Group2 respectively is 1410.59 m,1409.91 m,1408.76 m,1408.01 m,1407.09m;the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Putangzhe hamlet respectively is1406.39 m,1405.54 m,1404.10 m,1403.18 m,1402.05m;the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Duimen village respectively is 1418.77 m,1418.21 m,1417.25 m,1416.63 m,1415.88m;the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Baiyunan village respectively is 1415.77 m,1414.68 m,1412.83 m,1411.65 m,1410.22m;the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Aqie village respectively is 1440.47 m,1440.25 m,1439.88 m,1439.63 m,1439.33m;the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Leyan village respectively is 1433.55 m,1432.68 m,1431.19 m,1430.23 m,1429.07m;the designed peak flood flow level of p=1%,p=2%,p=5%,p=10%,p=20% of the control section in Putangzhe village respectively is 1400.26 m,399.17 m,1397.31 m,1396.11 m,1394.66 m.Analyzing the inundated area by DEM and geographic information technologies,making statistics of population,buildings,and others in different dangerous area,according to the inundated water level by actual measurement,the result can be calculated from the flood flow level,which shows the current flood control capacity in the calculated watershed as follows.Thses10 important reaches of Duoyishu village,Jiangtiansuo village,Caiyuan Group2,Caiyuan Group3,Putangzhe hamlet,Duimen village,Baiyunan village,Aqie village,Leyan village,Putangzhe village will be inundated in 12 years,8 years,3years,3 years,13 years,6 years,4 years,6 years,8 years,6 years.In general,in these 10 important reaches chosen from Banqiao watershed,8 reaches cannot resist the flood in 10 years,whose current flood control capacity is low.Moreover,in those 8 reaches,Caiyuan Group2,Caiyuan Group3,and Baiyunan village cannot resist the flood in 5 years,whose current flood control capacity is much low,but the risk of flood is much high.Therefore,the flood control capacity of vital villages along the river in Banqiao watershed needs to be improved urgently.