| When we opened the historical picture, as early as in1935when the Red Army enter intothe Yan’an, the Yan and Fen River Valley under the pagoda mountain are flooding, marching,military training zone which we can find in the photos or videos.After the founding of newChina, the urban construction of Yan’an are rapidly developed especially since the reform andopening up, the original zone which are used for flooding, marching, military training hasbeen built into high-rise buildings, the river becomes more and more narrow.So we canimagine that, if encounterextreme weather, the occurrence of serious debris flow,whether itwill affect on Yan’an? How big is the risk of disaster? How to respond and mitigate disasterrisk?Yan’an is a prone areas of landslide, collapse and debris flow disaster which are locatedin the middle of the Loess Plateau,there are two cases to support this disaster in this area, Yanriver occurrence of a large flood disaster In July61977,the water flow of Yan’an hydrologicalstation peak flow of7200m~3/s,134people were killed,4132houses collapsed, destroyed6.5million acre of farmland and destroyed more than200dam; In August3,1993, the water flowof Yan’an hydrological station reached3000m~3/s,17.5million people were affected, and thedeath tolls of13people,160million yuan of direct economic losses. Due to global climatechange and large-scale impacts of human activities, especially the explosive growth of the city,the prevention of debris flow situation in yan’an has changed fundamentally;debris flowdisaster preventionin Yan’an has becomean important and urgent problem to be solved.The article is based on the results of the detailed investigation, risk management,monitoring and early warning, and other research projects of geological disasters in yan’an,which are studied by the China Geological Survey Bureau.The study area is yan’an citywhich are located in the central Loess Plateau. The research objectis debris flow disaster.Theresearch methods of debris flow disaster risk evaluation are data collection, hydrologicalanalysis, remote sensing interpretation and field investigation, and propose a measure ofdebris flow disaster risk mitigation.The main research and understanding as follows:1.Through hydrological frequency analysis and submergence analysis method, obtainedpeak flow and submerged area at different debris flow frequencies in the Yan’an main city river. The total length of study river is about15km, Yan river between Yan’an university newarea and Luojiaping; Xichuan river between Xiaobian valley bridge to the confluence of Shifoditch; Nanchuan river between Yan valley to intersection, Dufuchuan bridge to Theconfluence of Hutong bridge. Arrived at the frequency of Debris Flow Disaster and carriedout hazard zonation.2.According to urban planning and construction data, remote sensing interpretation andfield verificationsurveysand other methods to analyze the distribution of population, buildingsand infrastructure, toclarify the various types of vulnerability and temporalprobability,revealing the dangers of the debris flow disaster.3.Through the function of classification statistics and mapping in ArcGIS,to calculate themultiply of risk and harmfulness in each cell.And propose a measure of debris flow disasterrisk mitigation through the size of the risk.4.According to the result of risk evaluation shows, the total area of risk is6.69km~2, thehigh-risk area is about0.13km~2,1.8%of the total area; slightly higher risk area isapproximately1.77km~2,25.4%of the total area; medium risk area is about1.36km~2,19.5%ofthe total area; slightly lower risk area isabout2.42km~2,34.8%of the total area; low-risk areasis about1.29km~2,18.5%of the total area.Based on the above findings, the development of Yan’an city flood control planning, toprovide flood disaster mitigation measures, explore and summarize a set of debris flowdisaster risk assessment technology and methods for other cities and towns in Loess Plateau. |
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