| Xiuyan Man Autonomous County of Liaoning province (hereinafter referred toas Xiuyan County) debris flow disasters has long history. In the on-the-spotinvestigation found that a large number of old debris flow deposits, debris flowactivities throughout the county each villages and towns. Almost every year of XiuyanCounty where has the scales and sizes of debris flow disasters, a recent large-scaledebris flow disaster for2012. In addition, Xiuyan County since1949, respectively in1960, in1982, in1987, in1989, in1990, in1997and in2002in different regionslarger-scale debris flow disasters have been occurred there. Especially threesuper-large scale debris flow disasters are the most serious in the80’s. Therefore,strengthens to investigation and study mechanism and characteristics of debris flowdisaster in Xiuyan County of Liaoning province, timely and accurate warning orforecast to debris flow, to protect people’s life and property safety, it is urgent.This paper based on the census results of debris flow disasters of Xiuyan Countyin the early1990’s of Institute of Mountain disasters and Environment, ChineseAcademy of Sciences＆Ministry of Water Conservancy, through the on-the-spotinvestigation of characteristics of debris flow disaster in Xiuyan County, and refer tothe study of the topographic factor on the gully-shaped debris flow forecasting modelwhich apply to the gully bed starting mechanism, select more suitable for reflectingthe formation characteristics of debris flow formation in Xiuyan County such as basinarea(A), gully bed longitudinal slope (J) and the slope gradient(S) as the elements ofthe topographic conditions of debris flow in this county. By comparing the correlationon basin area(A), gully bed longitudinal slope (J) and the slope gradient(S) betweendebris flow gully and no debris flow gully in the group of debris flow disaster area in2012, this paper concluded the topography critical value between debris flow gullyand no debris flow gully, and applies the law in1982,1987and1989debris flowdisaster area for validation. Finally discusses the other two debris flow formationfactors-geological condition and rainfall condition about Xiuyan County, to obtain therainfall factor be suitable for the characteristics of the debris flow about XiuyanCounty, then compare the correlation on rainfall condition and topographic condition between debris flow gully and no debris flow gully, a composite factor are obtainedwhich affect debris flow development and it is for the whole of Xiuyan County hasuniversal applicability. Main conclusions are as follows:(1) The source caused the outbreak of debris flow of Xiuyan County in Liaoningprovince not only derived from the gully bed material starting, also larger part of thesource derived from the shallow collapse(including slump) from the slope on bothsides of the gully, this is closely related to the slope gradient on both sides of the gully.The debris flow of Xiuyan County not only has the characteristics of gully-shapeddebris flow, also has the characteristics of slope-shaped debris flow.(2) Basin slope gradient has an important influence to the development oflandslide or collapse and slope debris flow on the whole Xiuyan County. TheSensitive area slope is25°to45°. Therefore, could uses25°to45°slope areapercentage accounted for the entire gully area as the object of study to slope factor intopographic condition of Xiuyan County debris flow.(3) By comparing the correlation on basin area(A) and Sensitive slope(25°to45°) area percentage(s) between debris flow gully and no debris flow gully, it isconcluded that the expressions of topographic G-factor(G=S(A/A0)0.2) as theclassification standard between debris flow gully and no debris flow gully: When G≥Cr, the gully can be determined for debris flow gully. G is a dimensionless factor.(4) Through the comprehensive analysis on basin area(A), gully bed longitudinalslope (J) and the slope gradient(S) between debris flow gully and no debris flow gully,get a comprehensive topographic T-factor: T=S(A/A0)0.2J0.3, it can better represent thetopographic conditions for development of debris flow gully. Through the topographicT-factor, the possibility of gullies can develop into debris flow gully in XiuyanCounty could be divided, which is divided into four levels: the possibility is verysmall; the possibility is small; the possibility is medium and the possibility is verylarge. T is a dimensionless factor. In the integrated topographic T-factor, we can seethat the weight of each topographic factor. The biggest impact topographic factor fordevelopment of debris flow of Xiuyan County is the slope gradient. Then, in turn, isthe longitudinal slope and the basin area.(5) Due to the adaptive ability in different areas to debris flow developmentconditions have different standards, the critical value of topographic factor betweendebris flow gully and no debris flow gully between will also be different.(6) The debris flow of Xiuyan County has quite part of the source derived fromthe shallow collapse(including slump) from the slope on both sides of the gully, the prophase rainfall plays an important role in the formation of shallow collapse. The rainfall factor of Xiuyan County can be represented as R,R=(B+5I)/R0Cv. R is a dimensionless factor.(7) By comparing the correlation on the topographic T-factor and the rainfall R-factor between debris flow gully and no debris flow gully in Xiuyan County, to explore the critical conditions between the debris flow gully and the no debris flow, getting the compound for determining P-factor(P=RT0.45) expression. Composite P-factor can judge the possibility of gully development into debris flow in Xiuyan County, and is divided into four grades:the possibility is very small; the possibility is small; the possibility is medium and the possibility is very large. P is a dimensionless factor.(8) Through the expression of compound P-factor can be seen, in the development condition of debris flow in Xiuyan County, rainfall conditions weight is higher than topographic conditions, is more important. Using composite P-factor, can provide the basis for the establishment and the further research of early warning and forecasting model of debris flow in Xiuyan Counties... |
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