Mountain Flood Risk Assessment Of Ziyang County Based On GIS

Ziyang county,in the south of Shaanxi Province,is located in north foothills of Daba Mountains.It is belongs to subtropical monsoon,with rich rainfall.Over the years,by the influence of climate conditions,topography,geological structure,and human engineering activities,mountain torrent disaster occurred frequently,caused a mass of casualties and economic loss.Based on sufficient mountain torrent data of Ziyang county and GIS,the causes of mountain torrent were analyzed,and mountain flood hazard,social economic vulnerability,and mountain flood risk were evaluated,obtaining the following results:(1)According to the distribution of flood marks investigated,compute peak flows of Yangzhuan River and Raoxi River in “7.13” flood of 2000 and “7.18” flood of 2010.The results show that the peak flows of these two river of flood in 2000 was all greater than the peak flows of flood in 2010.(2)The causes of Ziyang mountain torrent disaster were analyzed in respect of rainfall,topography,geological structure and social economic factors,indicating that precipitation is a direct and dynamic factor in the formation process of mountain torrent disasters,steep slope of rocks provides gravitational potential energy conditions,the loose solid matter is a material basis,and unreasonable human activities contributes to the risk of mountain flood disasters.(3)Based on local conditions,the mountain torrent disaster risk assessment index system was built,choosing rainfall,elevation,gradient,and soil type as mountain flood hazard assessment indicators,and choosing population density and land-use type as social economic vulnerability assessment indicators.These indicators were digitized by GIS,and were classified and standard processed by nature breaks,obtaining distribution and spatial classification of each index,and analyzing the spatial distribution of each index.(4)The weight of each index was obtained by analytic hierarchy process(ahp).The results show that for the factors of mountain flood hazard,the weight of rainfall is the largest,followed by elevation,and soil type has the least weight.For the factors of social economic vulnerability,the weight of population density is larger than land-use type.(5)The mountain flood risk assessment model was built based on the formula of “risk=danger×vulnerability” and the method of weighted mean.By the function of ArcGIS spatial analysis,mountain flood hazard,social economic vulnerability,and mountain flood risk of Ziyang county was analyzed.The regional maps of mountain flood hazard,social economic vulnerability,and the flood risk were given,finding that the assessment results reflect the current situation actually.