Research On Quantitative Geomorphologic Indices Of Bailongjiang Drainage Basin In The Eastern Tibet Plateau Based On Digital Elevation Models

More and more attentions have been paid to semi-quantitative and quantitative geomorphology research with the development of digital elevation model and spatial analysis technology. People use a variety of different geomorphic parameters to quantitatively depict topographical features, revealing the stage of landscape development, and the assessment of regional tectonic activity level. However, there are still some problems not be solved. For example, what is the correlation among these geomorphic indices, how can we use multiple geomorphic indices to depict the topographical features accurately, and to assess the relative tectonic activity of the large regions.Bailongjiang drainage basin covers an area of31808km2and is located in the transition zone between Tibetan Plateau and Tibet plateau. It’s one of the most serious disaster area for debris flow and landslide in China. The north-south seismic belt of China goes across this area. Active tectonic records the interplay between the Tibetan Plateau uplift and the different movement of faults. This region is a natural experiment to do the research on the above problems. The understand about the stage of landscape development and geomorphic space differentiation will deepen to know the effect about the uplift of Tibet Plateau and the occurrence regularity of landslides. With the constructed geomorphic indices, we do our research on the correlation of some basic geomorphic parameters, the stage of landscape development, the assessment of relative tectonic activity. The geological background including river terrace, distribution of earthquake, faults activity are all analyzed to recognize the spatial variation and intrinsic motivation about the difference of these geomorphic indices. It can be concluded as the following:(1) A new macro geomorphic parameter is introduced to reflet the height of bump of ground elevation relative to mean elevation.(2) There are some correlation among macro factor relief and altitude difference, average slope and average slope of slope. A model can be constructed to predicate the relief amplitude based on these micro geomorphic factors.(3) We carry out a study on the longitudinal profile of the32rivers, by fitting the characteristics of the river longitudinal profile using four function patterns, and analyzing the evolution process of the32river’s longitudinal profile based on the stream-power incision model. It can be concluded that tectonic activity play an important role in this region’s geomorphic indices and the upward-convex features of the profiles, the evolution phase of the river topographic form have not got to the steady state.(4) Elevation-relief ratio is the most accurate and convenient method to calculate hypsometric index (HI). The HI of sub-basins extracted by the accumulation area10km2can reflect the effect of tectonic with the development of mature, there are spatial difference from northwest to southeast and spatially correspond to the hanging walls of thrust faults. The spatial distributions of HI calculated based on analysis mask do not show clear spatial patterns and correlation with mean elevation and relief amplitude. HI are independent on the resolution of DEM and lithology but are scale influenced. The hot spots define the uplift of crust and active faults in the upstream of Bailongjiang basin> the cold spots define the downstream of Bailongjiang and some river valley regions.(5) The abnormal stream length-gradient index reflect the effect of active faults. The asymmetric factor reflect the east-ward extrusion of Tibetan plateau. The appropriate geomorphic indices are constructed to assess the relative tectonic activity, four classes of relative tectonic activity were defined:Class1(very high relative tectonic activity,5.5%in the area); Class2(high,54%); Class3(moderate,24.1%) and Class4(low,16.4%). These results are consistent with the division of neo-tectonic element.(6) Through the analysis of geological background, It proves that the difference of the geomorphic indices between mid-upstream and downstream, the spatial difference of relative tectonic activity level could reflect the absorption and transformation about the movement between East Kunlun fault and West Qinling fault, the extension to the north of Bailongjiang fault area by rapid uplift process of Minshan, the shielding effect of Minshan to decrease the tectonic activity level of Longmenshan fault.