The Study Of Shape Features Of Debris Fan And Deposit Area In The Milin County Along YarlungZangbo River

Milin County is located in the YarlungZangbo River valley with high mountains, steep slops and lithology broken which is under the affect of the YarlungZangbo River suture tectonic belt, and the activity of the tectonic movement and seismic in this area are frequently. There are many debris flow valleys in the two side along the river because of the strongly cutting of the mountains surface which are caused by the regional tectonic movement and steep terrain. In recent years, with the economic development of Milin County, the human activity along the river was increased, and the potential dangerous people would suffered will be increased in constantly. Therefore, it is needed to study the characteristics of the debris fan and debris flow hazard in this area in order to guide residents along the river taking into the rational production activities on the debris fans. At the same, it also could be provide design considerations for highway departments and offer suggestions for the railway sector to select the railway line.The article firstly study the morphological characteristics of the debris fans by means of the remote sensing combined with field investigation from the aspects such as the flat morphology, the fan area and the slope of the fan. There are 101 debris flows in total in the study area, the most of which have formed the alluvial fan. As a result of the new tectonic movement and the erosion of the river and the gully, the flat morphology of the debris flow fans have a variety of forms, the typical of which include sector, ginkgo leaf-shaped, stack-shaped, lens-shaped and other types. For Some gully which the drainage area is large, we could find that their debris fans also show certain combination of characteristics in the horizontal. While for a single debris flow, there also to be some shape deformation about the fan such as mosaic-type, lateral mosaic-type, overlapping style and inside stack style because of the uplift of the fan or the incision of the channel caused by the new tectonic movement. In order to analyze the correlation between the deposition area of the debris flow and the topography parameters of the catchment, the basic parameters of the catchments were extracted and taken statistics used remote sensing interpretation software like ArcGIS, and 34 catchments which the debris fans are whole were selected from the data set as a statistical analysis of the sample data. The results of the single factor regression analysis between the deposition area and each topography parameter of the catchment suggest that there exist obvious correlation with index between the deposition area and the catchment area, the main channel length or the catchment internal relief.According to the research of related fields at home and abroad, this paper choose the maximum deposition length as the factor to evaluate the maximum hazard range of debris flows at the base of the characteristics of debris flows in the study area. Reference to the research of the maximum runout distance of debris flow, we adopt sediment volume and catchment internal relief which are easy to get as factors to predict the maximum deposition length, combining with data of remote sensing interpretation and with field survey results. On the basis of the MATLAB functions and programming language, multiple regression models were used to determine the best model for the two given data set, and a prediction model for the maximum deposition length was established. In order to verify the reliability of the established model, an independent sample data set of 9 catchments which located downstream near the study area that were not used in the generation of the above model was used to test the regression equation. The validation proves that the relative errors between the predicted and field-measured values of the maximum deposition length of the debris flows are considered to be still acceptable for comparison with other empirical models. Although the model needs further improvement because there are several potential limitations such as the accuracy of remote sensing images and uncertainty of the volume of loose material that it couldn't provide accurate estimates of the maximum deposition length, it also could be used to provide preliminary estimates in the area where the geological and environment background are similar to the study area for site selection related to engineering activities.