Geomorphic Study Of The Jinsha River Valley In Baihetan Reach Based On Aster G-DEM

The lower reaches of the Jinsha River range from Shigu of Yunnan Province to Xinshi of Sichuan Province, are about 1305 km long. Drainage evolution history of the upper Yangtze River, which records the uplift of the Tibetan Plateau, has drawn much attention. Caused by river capture or not? The genesis of the Jinsha River has been controversial for a long time. The Jinsha River flows northward in Baihetan reach which connects the Chuan River to its east, and is the last part of the "W" shape of drainage structure. Previous studies mainly focused on Shigu, Panzhihua and other regions, while few studies have been made on this area.Previous studies mostly relied on topographic map. geological map and field survey, analyzed the evolution of the lower reaches of Jinsha River according to its drainage structure, landform of river valley, characteristics of terraces and alluvial sediments. This study will download the topographic data at a 30m resolution from Aster G-DEM and adopt the ArcGIS spatial analysis technique. I extracted and analyzed several terrain factors from the DEM in the area of Baihetan reach, for example, relief, slope, cross-section.I found that there are several planar landforms developed in the study area, of which the one in height of～2500m represents a well developed denudation surface consisting of straths. The main characteristics of the Baihetan canyon includes:(1) the height of the valley shoulder equals to the～2500 m denudation surface. (2) Transverse sections of the Jinsha River show the valley is in asymmetric "V" shape, valley slope on the right bank is steeper, of average slope about 40°, the average slope on left bank is about 20°, and a number of terraces developed on left bank; (3) Baihetan reach can be further divided into southern and northern segments.I also found sedimentological evidences indicating a southward-flowing paleo-drainage, such as alluvial sand and gravels, in Dongchuan and Gongshan. And there are very thick fluvial or lacustrine sediments in Songming region, south of Gongshan, suggesting the existence of a large river at that time.The evidences implying intensive and rapid incision of the Jinsha River are:(1) There are hanging valleys on steep valley side; (2) Headward erosion occurred on tributaries, and knickpoints have risen to～2500 m; (3) There are wide spread gravitational landforms along canyon valley. I estimated the incision rate of Baihetan Section based on the special terraces. The onset of the incision is approximately 4-5Ma ago by extrapolation.In summary, in the area near Baihetan reach of Jinsha river, the river flowed southward on the denudation surface during the early stage. About 4--5Ma ago, headward erosion of Chuan River occurred after the regional tectonic uplift. The Chuan River captured the southward-flowing river, and thus turned it to be one part of the primal Jinsha River. This result will help us understand the evolution history of the Jinsha River and its relationship with the uplift of the Tibetan Plateau.