Research On Feature And Formation Of Debris-flow In Anjia Gully, Wenchuan County

Anjia gully is located in Mianhu town,Wenchuan County, belongs to "5.12" earthquake epicenter. And geologically located in the center of the Longmen Shan fault zone, which is the hardest hit by the’5.12’earthquake disaster. The devastating earthquake not only caused casualties and severe economic damage to property, but also induced a large number of collapses, landslides, mudslides and other secondary geological disasters. These series of deadly geological disasters not only seriously jeopardize the life and property safety of surrounding residents, a more serious impact to the implementation of disaster recovery and reconstruction work.With a debris flow had been generated many years before, Anjia Gully erupt the new occurrences of a large number of landslides, collapse, unstable slopes, and other secondary geological disasters. Adverse geological phenomena of the groove provides a large source of loose solids, landslides stability was largely decreased, the possibility of an outbreak of large-scale debris flows comes up. At present, the debris flow cause a high risk to a group of86households of more than301people’s lives and property safety, and the State Road NO.213and the Wenchuan highway transportation routes pose a serious threat. These problems are emergency geological disaster in Wenchuan County.Therefore, the study of the debris flow gullies in order to protect lives and property of local residents and the state-owned economy has practical significance, it can also provide a reliable reference to the debris flow disaster management in the region.In this paper, several aspects of the Anjia gully the features and formation conditions was debated: 1) Statistics of the provenance of the study area, the channel conditions, the rainfall, combined with the study area historical disaster situations. Anjia gully debris flow is a type of rainfall-induced debris flow. During the debris flow was forming, gully within the deep valley, cross-strait cliff, scarp distribution channel which is narrow, longitudinal drop, multi-or water distribution. Special terrain conditions for the convergence of water and sediment to provide a favorable conditions. After the5.12" earthquake, the development of a large number of the ditch within slumping, unstable slopes, and other adverse geological phenomena caused a large solid sources of debris flow, with the favorable Geomorphology condition, once a heavy rainstorm occurred, commonly in the June or July, a debris flow can be possibly generated.2) the dynamic characteristics were calculated, including the precipitation in5years,10years,20years, the100-year rainstorm return, And the velocity, impact force of movement characteristic value for the future governance a more credible references. Then the River BLOCKING possibility was analysis, for the solid materials is playing a more important role than the fluid source in the generation of debris flow in this catchment, plus the large differences of flow velocity between the Minjiang River and debris flow, a low possibility of BLOCKING was concluded.3) Research on the morphology of the fan body shows that the accumulation of fan bodies with multi-phase nature, and the Anjia gully debris flow experienced at least one cycle of debris-flow which including a period of formative years-the period of development-a period of recession-a period of rest. Different positions of the particle size distribution of debris flow relationship shows different hydrodynamic conditions and the erosion and deposition characteristics in different part of channel. Mid-upper segment longitudinal drop and erosion and deposition characterized by erosion, However, the downstream valley longitudinal moderate and erosion and deposition characteristics shows a feature of depositing.4) through the formation conditions of two-dimensional physics experiment simulates the formation of debris flow, builds the debris flow critical gradient formula, flow empirical formula, calculated the amount of flow, experimentally inferred the difference between the two conditions will increased with the increasing slope angel. From a experimental aspect to concluded the subject area was being a dangerous phase already.5)Through the data got from the field wild and in laboratory,the author proposes a suggestion accord to protection measure, to build drainage canal at the down stream part of catchment, to lower the bend curvature, to induce the release materials to the Min jiang river, thus can ensure the safety of the people living on the sedimentary fan.Finally analysis that after the earthquake, in the research area landslides and other adverse geological phenomena increased, generated more loose solids sources than ever before, the current accumulation of loose solids source volume has exceeded the sources calculated during the1976debris flow. Therefore the large rainstorm, will great possibly lead to a large-scale debris flows. Then experiment to simulate the the Anjia gully encountered heavy rainfall,the results affirmed the conclusion made in the former chapter, a series of formulas was builded to valued the realistic situation thus provide a sound reference to the after-earthquake recover measure and prevention project of secondary debris flow.