Risk Assmessment Of Debris Flow In Chifeng Pumped Storage Power Station In Inner Mongolia Based On GIS

Debris flow disaster occurs frequently in China, and it has caused enormouseconomic losses and casualties every year, which can have a severe effect onhumanity’s existing and developing surroundings. As a basis for disaster preventionand reduction, debris flow risk assessment can not only reflect the hazard anddevelopment tendency of debris flow, but also predict the damage degree, thus thedebris flow risk assessment can provide certain decision basis for the decision-makerand has become one of the foci in debris flow research. Taking Dashimen valley inChifeng pumped storage power station in Inner Mongolia as an example in this paper,GIS was used in risk and vulnerability zoning, and then risk assessment wascompleted. Besides certain research significance, the word can also provide scientificevidences for ensuring the safe operation of the power station.Dashimen valley debris flow is located in the middle-mountain area at an altitudeof1100~1700m, and the strata exposed in this area consist Carboniferous, Permian,Jurassic, Neogene and Quaternary System. There is no regional deep-fault in this areaand its basic seismic intensity is lower than VI degree. The research area belongs tothe middle temperate continental monsoon climate and its annual precipitation isbetween250to540mm. The groundwater contains bedrock fissure water andquaternary pore water. The vegetation coverage rate in the research area is generallyhigh.According to the standards in "Specification of geological investigation fordebris flow stabilization"(DZ/T0220-2006), Dashimen valley debris flow is extremely low-frequency, and it has weak activity and strong ability to cause disasters.The development stage of the debris flow is in declining phase and its easy-happeningdegree is easy-happening.Topography factors such as elevation and slope are extracted with the help ofArcGIS, and then buffer analysis and superposition calculation are conducted in riskzoning, vulnerability zoning and venture zoning. The results show that the highdanger area is mainly distributed on both sides of the main channel and in the areawith gentle slope in the deposition fan, vulnerability zoning is highly correlated withthe distribution of hazard bearing body, and the risk near the dam and road is higher.Due to the difference in the monotonicity for risk factors and the nonlinearrelationship between the primary risk factors and secondary risk factors in theevaluation, scatter diagrams and Spearman rank correlation coefficient are combinedto select the secondary risk factors in the process of hazard assessment. The factorsselected include the most volume of once flow, occurring frequency, main channellength, maximum relative altitude in drainage area, incising density, bendingcoefficient of major ditch bed, the volume of loose material, length proportion ofdebris supplement section and vegetation coverage rate. After obtaining the weights ofevaluation factors on the basis of Spearman rank correlation coefficient, thehazard-assessment model is established, and the debris flow hazard assessment resultshows that Dashimen valley debris flow is of low hazardousness with hazard degreeof0.3224. Since there are no residents, commercial facilities and economic activitiesin the influence scope of the deposition fan, only vulnerability of environment andmaterial is chosen in the vulnerability assessment. Vulnerable value of the dam, roadand farmland is mainly considered to obtain the vulnerability degree, and the resultshows that Dashimen valley debris flow is moderate vulnerable.On the base of assessment results of hazard and vulnerability, the risk degree isobtained by superposition calculation in ArcGIS, and it has been known thatDashimen valley debris flow is of medium risk with risk degree of0.19, which meansthat risk exits with benefits in this area and risk management and reducing measuresshould be considered during development. Grille-dam is recommend for sediment retaining and drainage, and biological measures should be taken at the same time toincrease the vegetation coverage rate and conserve soil and water, and finally achievethe aim to control debris flow fundamentally.