Hazard Assessment On Potential Debris Flows In Wenchuan County After Wenchuan Earthquake Based On RS, GIS & GPS

China is one of the few countries in the world which suffer most seriousgeological disasters, the collapse, landslide, debris low and other geological disastersespecially in the western mountains region. Followed"The Greate TangshanEarthquake"in 1976 and"Yunnan lancang, Gengma earthquake"in 1988, theWenchuan earthquake in China on"5.12", 2008 occurred whose magnitude was morethan seven at first time. It caused a great deal of life and property damage. Thedebris flow has a great impact on the normal life in the western mountains. Once thedebris flow broke out, it will cause a large number of casualties and economic loses,even destroy the whole town in the mountainous urban areas. It has seriouseconomic constraints of the local construction and development of mountain areas.Currently, the research and mitigation of debris flow prevention becomes more andmore important. Strengthening researches of the debris, preventing, mitigating andforecasting disaster in town is of great significance.In this paper, the author summarized previous relevant research experience afterthe earthquake and deeply analyzed the impact factors of debris flow activity basedon the source conditions of landslides and collapse, spatial and temporal distributionand distribution characteristics. The author used different model of debris flowhazard assessment, studied potential hazard on the specific region respectively forthe evaluation grid and watershed unit. The article got the following understandings.(1) Induced heavy rainfall, collapse landslide provided Source for debris flowdisaster. The major impact on the performance follows: destruction of towns,villages, farmlands and water conservancy facilities, agricultural production, disruption of transport, stoppage of rivers and even formation of a barrier lake. It didserious harm to post-earthquake reconstruction.(2)Research analyzed mechanism of the debris flow's occurrence anddevelopment in the area after the earthquake and considered that the earthquakedestroyed the lithological structure in the study area and induced landslides and othergeological disasters, which gives a lot of loose pieces accumulation of debrismaterial which is the main factors of causing the Wenchuan earthquake.(3) According to post-earthquake aerial images, combined with disaster pointsof information and topography, geological structure and spatial distribution of water.The author did the interpretation of seismic-induced landslides and other geologicaldisasters point information and analyzed spatial and temporal distribution of debrisflow in the study area after the earthquake. Then analyzed and summarized theimpact of various factors such as topography, geology, hydrology and meteorologyand the impact of human activities, landslides after the earthquake.(4)In this paper, by means of AHP method, the author selected ten evaluationindexes, such as the gully slope, relative elevation, lithology of the compositestructure, the annual maximum daily rainfall, land use pattern and population densityand constructed assessment, model of a unit grid debris flow hazard. The applicationof AHP method determined the corresponding weight factor of each index value, thechoice of GIS technology for spatial analysis of the index factors and the assignmentand completed the study using the weighted sum model of debris flow hazardassessment area. According to the index theory of classification, the study area willeventually be divided into four debris flow hazard level.(5) According to interpreted from aerial images with map information fordisaster point, the author determined the 57 selected cells as a potential debris flowbasin. The author also used improved overall after the earthquake, and establishedsingle debris flow risk assessment model by used evaluation factor of the total debrisflow and gully slope. Finally, completed risk evaluation of 57 debris flow.Combination of field survey and relevant information, the results with a strongfunctionary showed consistency between evaluation results and the actual situation.