Solid Source Characteristics And Early Warning Of Debris Flow In Zhouqu

Debris flow is among the most devastating secondary geological disasters after the earthquake,which directly affects post-disaster reconstruction and the safety of life and property of the people in the disaster area.In this paper,the study area is Nanyu Ravine in Zhouqu County,on which field investigation and indoor and outdoor tests are based,and remote sensing technology and computer software are applied to study the source composition,forming conditions,starting mode,early warning and forecast of debris flow disasters in highly seismic regions.The debris flow disasters occurred on August 11,2010 was analyzed from site scale,macro scale and micro scale.The TM remote sensing image was used as data source to interpret the geological conditions of the key section of the Nanyu Ravine debris flow,the development status of the unfavorable geological body and the distribution characteristics of the loose solid source.On this basis,combined with field investigation,the gully characteristics,source reserves,and the formation conditions and startup process of the debris flow in the study area were analyzed.According to the test results and calculation results,the genetic types,starting mode and mechanism of Nanyu Ravine debris flow are discussed,aiming to understand this type of debris flow in depth and to provide scientific reference and recommendations for early warning and forecast as well as for disaster prevention and reduction.From the microscopic point of view,the internal characteristics of loose solids in the area and the water quality characteristics of rivers in the basin were studied.The finite element software Geostudio was used to simulate and analyze the seepage process of the destabilized debris flow caused by the unfavorable geological bodies in the study area under the action of rainfall.A new approach for early warning and forecast of rainfall-triggered debris flows in mountainous basins lacking meteorological data is suggested by way of water quality monitoring method.Finally,a comprehensive evaluation of the risk degree of debris flow in Nanyu Ravine was carried out via fuzzy analytic hierarchy process,and the division of geological disaster prevention and control was provided accordingly,along with corresponding suggestions.This study mainly serves for the early warning and forecast of debris flow disasters in highly seismic regions.The main works and achievements are as follows:1.Through field investigation and data review,the topography and geomorphology of the main gully and branches,regional geological environment,hydrogeological conditions,gully and valley characteristics,bank slope height,channel erosion,as well as reserve,distribution,and replenishment of loose solid sources were understood.Typical geomorphological sites were selected for key analysis.2.With Mapgis,CAD,Googleearth,PS and other software,remote sensing interpretation signs such as landslides,collapses,mud flows,and soil vegetation within the Nanyu Ravine basin were established by extracting information from TM remote sensing image data sources.Based on the comparative analysis of remote sensing data and existing data,a remote sensing interpretation map of key geological environment and geological disasters in the Nanyu Ravine basin was compiled by using a combined technical route of compilation and verification.From the macro perspective,the characteristics of spatial distribution of debris flow sources and the characteristics of transformation and migration were analyzed,which lays a foundation for the study of disaster mechanism of debris flows.3.Field tests and laboratory tests were conducted at typical geological disaster sites,and the internal characteristics(basic physical properties,particle size distribution,infiltration characteristics,shear strength,CEC,ESP,mineral content,salt content and salt leaching,etc.)of loose solids sources were studied from a microscopic perspective,providing reliable parameters for numerical simulation analysis and disaster prevention and reduction.4.Under the rainfall and non-rainfall modes,water quality analysis and monitoring were conducted on the rivers in the main gully and branches of the Nanyu Ravine basin.It was found that the river water quality was not only correlated to natural factors like gully length,gully area and vegetation coverage rate,but also controlled by the volume of rainfall.In a given basin,the water quality of the river is only controlled by the volume of rainfall.Therefore,a new approach for early warning and forecast of debris flow in small basins is proposed.5.Based on the test results,a quantitative relationship between rainfall and river water quality was fitted and an early warning and forecast model was established.After being verified by examples,this method is proved to be convenient,reliable and practical,and it has certain guidance for the early warning and forecast of geological disasters.6.Fuzzy Analytic Hierarchy Process(AHP)was applied for a comprehensive evaluation of the risk degree of debris flow in Nanyu Ravine.Based on the evaluation results,the zoning map of geological disaster prevention and control in the study area was drawn,and relevant prevention and control suggestions were given in combination with the actual situation.