| A mass of the collapse and the landslide and the debris flow and the dammed lake of the secondary of the mountainous region disaster were by induced in WenChuan.On "5.12",a large number of slump provide the ample of the solid matter source for the debris flow in this earthquake’s formative process.the disaster area of WenChuan appeared the high-frequency and group of debris flow in every wet-season after earthquake,and also there are the scope of concentrate and the pole-strength of the collapsing force in the grope of debris flow,that threats seriously the safety of the life and property in disaster area.Finally,It’s more contenty for that forecasts properly the group of debris flow of the formation condition and controls the damage that the group of debris flow cause.and also it’s the effective on the basis of theory for the disaster prevention and reduction in the disaster area.The topographic condition of the debris flow on formation of the three condition,is the foundation of condition on the debris flow’s occurrence,or conclusive condition,and also it’s possible for the debris flow’s occurence.In the debris flow’s developmental of the coteau that equipped with the topographic condition,the article studies the comprehensive of the topographic factor about the group of debris flow after earthquake,and discusses that the one of comprehensive factor expresses the critical topography value in the gully-shaped debris flow’s formation process about the topographic condition.When it studies the topographic condition of the debris flow’s formation.It must be in the same geological and rainfall conditions of the debris flow’s valley.For the group of debris flow speaking,that’s occurrence is very concentration,so,it’s very easy for in the neighbourhood of valley to find the similarity or same valley of the geological conditions.But to find the same rainfall condition of the valley is very hard,even if in the neighbouring of the valley.The inhomogeneity of the rainfall distribution results in the totally different of the rainfall.It’s very favourable condition for the strong earthquake’s group of the debris flow.To study the geography fact about the gully-shape debris flow’s formation;the large-scale rainfall made the group of the debris flow valley’s rainfall seem relatively equality;and also in the small-scale rainfall can consider the condition of the rainfall more accordance,therefore,in similarity with the condition of the rainfall and geological.Contrasting the effect of the comprehensive of the topographic factor that is in debris flow’s formation.It makes that studies the singularity condition topographic condition for the effect of the debris flow’s formation become actuality.When the topographic condition that the group of the debris flow was studied in strong earthquake.Firstly,It must be sure that is the same of the part from riftzone.Secondly,the study region’s rainfall must be the same,then the stratum of lithology must be the same.In the same vally,in this condition that is prossess of the three factor,It can study that use a comprehensive topography factor replace all of the comprehensive of the topography factors,and also it can be sure the critival value of the topography that the debris flow occur possibility.Finally,It makes the comprehensive of topographic factor that obtain the conclusion from the above of the analysis,apply to others group of debris flow’s disaster valley for checking. So,It gains some of the conclusion as follow:(1) The gully-shape debris flow’s damage is very hard,most of the strong earthquake vally of the debris flow are the gully-shape debris flow. Start the formation mechanism of this debris flow channel formed within the powerful flood ditch bed of solid material,this type of debris flow formation mechanism of severe erosion.As the phenomenon of "fire hose"tu start the gully bed of solid material,eventually,leading to debris flow formation. Therefore,the main researth debris flow terrain factors valley debris flow.The formation of debris flow often occurs in the formation of the district,forming region a dominant role in the formation of debris flow,so the topographic conditions of the study of debris flow is mainly concentrated in the forming region.(2) The article analysises the main topography partments about the model valley of the debris flow channel,Both that development level of ho’and the channel gradient of Jo are dimensionless group,and also both of them are linearity of direct proportion.So the development level was by ingored.Some of topography partments,as follows:form factor of Fo and the channel gradient of Jo and the hillside degree of S and formative region’s area of Ao.(3) Between the Fo and Jo and S and Ao are by contrasted,for the49debris flow channel on "8.13" In Longchi town.Finally,It obtains the critical topography factor of T(dimensionless) that its expression is T=F0×J0,about the debris flow that occur possibily.In the same rainfall and geological conditions, The larger the factor T,the higher the probability of debris flow initiation.A larger T-factor is needed in the footwall area in order to form a debris flow. On the contrary smaller T-factors are needed to initiate debris flows situated in the hanging wall area. The larger the distance to the triggering fault of the earthquake,the larger is the threshold value needed for the T-factor.The critical T-factor for a large watershed area (≥1km2) is less than the critical T-factor for a small watershed area (<1km2).The T-factor forming debris flows in limestone area is larger than the one in the sandstone and shale area.(4) Analyzed T factor and AO of formative region, obtained new T factor of opography(no dimension), The equation is receive G factor which can express topography condition of forming debris flow and is closely connected with the main effect of drainage area in forming debris flow. In same condition of rainfall and geology, bigger G factor can cause higher possibility of debris flow. As a whole, faulted zone in hanging wall has smaller G factor than footwall; The far near the faulted zone, the bigger of the G factor of topography.(5) Analyzed G factor and S of hillside degree, because of region difference in hillside, different region has different hillside degree, this article only research S of hillside degree in Longchi. The statistics showed hillside degree of debris flow in Longxi valley are20to50degree. Analyzed proportion of this range to obtain the relationship of G and S:M=G×S (no dimension);In same condition of rainfall and geology, bigger M factor can cause higher possibility of debris flow. As a whole, faulted zone in hanging wall need smaller M factor than footwall.(6) Applied T and G factors of typical zone to Yingxiu "8.14" groups of debris flow, Qingping "8.13" groups of debris flow, acquired the same conclusion in Longchi. This article has stronger significance in research of topography factor to forming debris flow. |
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