Evolution Characteristics Analysis And Hazard Prediction Of Ganxi Gulley Debris Flow In Beichuan After "5·12" Earthquake

Gangxi gulley is located in the middle of longmenshan area in "5.12" wenchuan earthquake induced collapse sliding body of more than 90, the volume of 36.05 x 106 m3, make it become a typical branch lander group affected by the earthquake hairstyle watershed mud-rock flow ditch. On September 24, 2008, August 7, 2010 and July 9, 2013 a massive mudslides, debris flow along a groove on both sides of the more than 400 residents of life and property caused great damage. Dry gulley earthquake debris flow has certain regularity of occurrence and development, studies its development characteristics, evolution trend and risk of landslides after a disaster management has important practical significance.This article through the analysis of Gangxi gulley debris flow development status after the quake, in the research of debris flow provenance, lose sand characteristics, accumulation, on the basis of analysis of the causes and evolution characteristics, and predict the evolution trend, and predictive evaluation of the gully, the following main achievements were obtained:(1) Gangxi gulley changes after the earthquake source, on the one hand, show the content source quantity increase or decrease, on the other hand show the content source type conversion. Early rainfall induced new collapse and slide channel source greatly increased; Over time, in the basin of vegetation recovery, provenance area is relatively less. Evolution process of different kinds of material sources vary, shore slope foot loose debris source evolution model for: lateral margin erosion â†' instability of slope failure; Ditch slope foot loose debris sources evolution model is: the new source erosion â†' instability of the slump; Evolution model for channel plugging type source: downcut â†'form a ravineâ†'congestion collapse â†'scour dam; Evolution model for slope type source: the slope erosion â†'channel launched; Debris flow provenance evolution model is: the surface drag â†' drop to scour incised.(2) "9.24" compared with "8.07" debris flow twice, the rainfall is less than the former, because the active source is the first a landslide and rainfall of consumption, together with the difference of rainfall, "8.07" relative "9.24" landslide lose sand size decreases, "7.09" heavy rain intensity is greater than the previous two, the equivalent of 50 years of rainfall, due to the large amount of active source than the previous two, together with the influence of the regulation project, therefore, increased rainfall in the cases, the debris flow scale instead of smaller.(3) After three times of landslide outbreak dry gulley evolution characteristics of sediment: early after mudslides, Gangxi gulley aggradations of the upstream, middle and lower reaches, and the middle sedimentation is relatively strong. Late with relatively smaller mudslides have outbreaks, the rains washed out, and the late management engineering and the effect of scouring and silting in upper and middle range reduced, the downstream alluvial amplitude decreases first, eventually turn deposition for blunt. With the decrease of the debris flow scale and the influence of the regulation project, large particle material has decreased in the debris flow deposits, the particulate matter increased, the average particle size decreases, and debris particles with preference, sorting bias., the upstream to the downstream channel deposit large particle content percentage increases first and then the change trend of performance, small particles content percentage change trend performance increase with the decrease of the first, the average particle size decreases, and particle size distribution of the first after rising downward trend.(4) With the decrease of the debris flow scale, branch debris flow accumulation scope without extension. Accumulation fan superimposed relationship of lap and Mosaic. In the early of the gully and the flood, under the action of lateral erosion, te 6 accumulation fan diminishing, retreat, now basically stable.(7) Since the "5.12" earthquake, completed a Gangxi gulley debris flow from loose solid material control to transport control type, transitional such an evolutionary process, now is still in a strong activity, but overall a downward trend, with the passage of time, the debris flow activities will be converted to loose solid material controlling, eventually returned to the state before the "5.12" earthquake. After using the analytic hierarchy process(ahp) to obtain the weight fuzzy comprehensive evaluation model is established for Gangxi gulley earthquake debris flow risk evaluation, the evaluation results for the high risk.