Debris Flows Sensitivity Analysis Of Minjiang River Of Yingxiu Section

The Wenchuan earthquake of May12,2008produced large amounts of loosematerial (landslide debris) that are still present on the steep slopes and in the gullies.This loose material creates an important hazard as strong rainfall can cause thedevelopment of devastating debris flows that will endanger there settled population anddestroy the result of reconstruction efforts. On14August2010, a total of21debrisflows were triggered by heavy rainfall around the town of Yingxiu, located near theepicenter of the Wenchuan earthquake. One of these debris flows produced a debrisdam, which then changed the course of the river and resulted in the flooding of thenewly reconstructed Yinxiu town. Prior to this catastrophic event, debris flow hazardhad been recognized in the region, but its potential for such widespread and devastatingimpacts was not fully appreciated. Our primary objective for this study was to analyzethe characteristics of the triggering rainfall and the sediment supply conditions leadingto this event. Our field observations show that even small debris flow catchment areashave caused widespread sediment deposition on the existing fans. It is concluded thatthe whole of the area shaken by the Wenchuan earthquake is more susceptible to debrisflows, initiated by localized heavy rainfall, than had been assumed earlier. The resultsof this study contribute to a better understanding of the conditions leading tocatastrophic debris flow events in the earthquake-hit area. This is essential for theimplementation of proper early warning, prevention, and mitigation measures as wellas a better land use planning in this area.A catastrophic earthquake usually intensively disturbs the slope bedrock andcreates an abundance of loose landslide debris on the slopes. This affects the stability ofthese slopes for a long period of time. The debris serves as source material for rainfall induced debris flows. Debris flows are triggered by a combination of three essentialfactors: sufficient available loose material, surface runoff, and steepness of thedrainage channels on the slopes. The relation between rainfall intensity and theinitiation of debris flows has been well examined in the past, but less attention has beenpaid to the sediment supply factor. Landslides caused by the earthquake increase theamount of loose (slope debris) material in the drainage channels and change thesediment supply condition. The impact of the Chi-Chi earthquake on subsequentrainfall-induced debris flows has been studied by various authors. Dong et al.(2009)used a discriminant model, which takes account of the debris budget, to study theinfluence of earthquakes on the subsequent occurrence of debris flows. Their studyshowed quantitatively that the occurrence of the1999Chi-Chi earthquake hadsignificant impact on the debris flow occurrence during subsequent typhoons. Bovisand Jakob (1999) and Jakob et al.(2005) highlighted the importance of sediment supplyon the frequency and magnitude of debris flows. Loose sediment material can bederived from channel fill, from new landslides on the slopes, or from the erosion ofexisting landslides. Strong earthquakes can play a major role in contributing to theaccumulation of sediment supply on hill slope and in channels.Debris flow of Yingxiu section of Minjiang river valley is a major disaster area ofWenchuan earthquake secondary disasters. Research area, which has beautiful naturalenvironment and natural geological disasters, seriously affecting the local economicdevelopment, and people’s life and property security. This article in-depth study andresearch of the predecessor’s research results, made a lot of detailed field investigation,collecting basin related characteristic parameters, and use the images of aircraft, etc.,Interpretation of21debris flow gully watershed disaster of the Minjiang river valley inYingxiu section, the analysis of debris flow distribution, development characteristicsand formation mechanism. Selection of mud-rock flow sensitivity evaluation factors inthe study area, data processing by applying the method of grey correlation evaluationfactors, combined with fuzzy comprehensive evaluation method for sensitivitypartitions. With GIS software finally make research in the debris flow ditchsusceptibility zoning map. Carry out specific work is as follows: Inductive analysis ofdebris flow distribution, development characteristics and formation mechanism of thestudy area; Research and analysis the influence factors of debris flow disasters in thestudy area, including direct or potential factors, and the role of the affecting factors, andpick out the main factors that determine evaluation factor for regional debris flow sensitivity in the study area partition; Determine debris flow sensitivity division ofYingxiu section of Minjiang river valley area, the principle of selecting factor anddetermine the factor weights, a mathematic model of the debris flow sensitivityevaluation. High-resolution remote sensing image based on Rapid Eye and ETMinvestigating21debris flows and the sensitivity evaluation, quantitative judgment21debris flow sensitivity of Yingxiu section of Minjiang river valley, Draw out highsensitive area, moderate sensitive area, light sensitive area and general sensitive area,analysis the relationship between Sensitivity of debris flow and pregnant disasterenvironment and the induced factors; According to the results of the debris flow valleysensitivity evaluation, based on the GIS platform of basic data, data processing and thevector quantization, for sensitive landslide zoning map; Use results of debris flowsensitivity division of Yingxiu section of Minjiang river valley, provide informationsupport to reconstruction for the town of Yingxiu, for the future of people’s life andeconomic development in the town of Yingxiu.