| Dujiangyan city of Sichuan province is located in the "5.12" Wenchuanearthquake harder-hit area, belongs to the strong debris flow activities area afterearthquake. The study area is located in the northwest of Dujiangyan city, which wereseriously affected by "5.12" Wenchuan earthquake. Many landslides were produced inthe terrain surface, which were resulting in a large number of loose materialsaccumulated in slope and channel. If the study area caught in a fierce storm, it couldprovide many material sources for debris flow formation. On August13,2010, a bigrainstorm occurred in the study area, which induced groups of debris flow and causedenormous losses. Some debris flow parts blocked of Longxi River, the overall upliftriver buried buildings and roads and have done a lot of trouble for post-earthquakereconstruction. Due to the complicated terrain conditions and easy to occurred largescale debris flows, risk evaluation is necessary in the region. Based on fieldinvestigation on August13,2010, through high resolution remote sensing imageinterpretation landslides, combined with a variety of mathematical and numericalsimulation method by FLO-2D, debris flow risk assessment would carry out. First ofall, based on the mathematical method of probability, sensitivity evaluation of debrisflow have been taken in the study area, and then through FLO-2D numericalsimulation method to study the hazard of debris flow risk assessment, and thevulnerability could be evaluated by nonlinear regression mathematical methods,finally quantitative risk evaluation of debris flow would conducted in the study area.Based on collected a large number of references, carried out detail fieldinvestigation and calculated the complex indoor works:Through the on-the-spot field investigation and multiphase deciphering of remotesensing data indoor, comprehensive analysis leads to the debris flow formation oftopography, hydrological and geological conditions, all collapse landslides of debrisflow were determined in terrain factors (elevation factor, slope factor, longitudinalslope factor), geological factor (lithology factor) and hydrological factors (gullydensity factor) of arbitrary classification under the condition of the probability ofcomprehensive discriminant value; According to the value of the probability of comprehensive discriminant, the high and low sensitivity in six evaluation factors ofspecific classification interval could be distinguished in originally arbitraryclassification conditions, thus the sensitivity interval in different evaluation factorscould be avoided the artificial boundary. According the sensitivity of the gradingrange, grade standards of debris flow was established in research area. Then from thearea to single gully susceptibility evaluation, combined three conditions in the terrain,hydrological, geological and grade reference standard, the score of single were got onthe six evaluation factor. Weights of evaluation factors were determined by greycorrelation method. Finally, combined with the dimensionless factor on behalf ofdebris flow on each evaluation factor score and the corresponding weights ofevaluation factors, the model of debris flow sensitivity were established.Through the analysis of the hydrological models, the new flood flow process linealgorithm was built based on integral mathematical thinking. This article adopts themethod of typical flood process amplifying line to solve the flood flow process line.First, flood volume was deduced by the rainfall, which determined by correspondingrainfall and river basin area. Another was derived according to the rainfall time T andthe area basin within the scope of the total flood flow WP, a similar form of integralalgorithm would be used to calculate each generalized rectangle of the flood process.Finally, the coordinate values of the flood process line were got by the debris flow setpoint catchment area. It is worth noting that if a debris flow has multiple sets of waterpoints, which could help divided the whole ditch basin range into different small basinarea.Under different rainfall frequency (once every five years, once every20years,once every50years, once every100years and once every200years), the importantdebris flows were carried out numerical simulation by FLO-2D software in the studyarea. The velocity and depth of debris flow were got from numerical simulation result,combinated debris flow outbreak frequency, debris flow hazard hierarchy standardand hazard map were established in the study area.In order to got all land use types of debris flow vulnerability in the study area,deep (h) and velocity (v) of debris flow and the bearing capacity of different land usetypes (p) as vulnerability assessment factors from the two aspects of the inherentcharacter of the debris flow and the bearing strength of different land use types. Bywriting programs in MATLAB software, the nonlinear regression model ofvulnerability was established. Building, road, river, green space of fragility value(Vvalue) and deep (h), velocity (v), bearing capacity (p) were used to regression test of significance, through the nonlinear fitting of three evaluation factors, the scope ofvulnerability comprehensive evaluation model was built in the study area.According to the hazard and vulnerability from the12debris flows in the studyarea, fully considering the mutual restriction and mutual coupling relations, the debrisflow quantitative risk evaluation standard and risk map was established in the studyarea. It can provide direct basis for the town of post-disaster reconstruction. |
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