滇西纵向岭谷区河谷形态特征、发育规律及成因

Valley Morphological Characteristics,Development Law and Their Cause in the Longitudinal Rang-gorge Region

为了揭示滇西纵向岭谷区河谷形态特征及其发育规律,采用1∶5万DEM图件,利用ARCG IS软件提取研究区41个河谷断面的有关基础数据,据此计算了河谷横断面的宽深比、半高宽深比、断面面积、凹度、不对称系数及河谷纵剖面特征的指标。结果表明,纵向岭谷区北部河谷横断面的宽深比很小,其宽深比在4～16间,但沿流向往南有明显增大的趋势,最大达到24。这是由于北部的构造抬升作用强从而引起该区更强列的河流下蚀作用的结果。河谷横断面的凹度显示大多数河谷属于“V”型谷,表明研究区的河流仍然以下切过程为主。谷宽不对称系数及谷面不对称系数揭示了研究区河谷横断面主要是左倾型河谷,即河谷断面上河道左部谷坡较缓,这是强势西南季风在河流左岸迎风坡形成强降水带和在河流右岸背风坡形成弱降水带的雨水差异侵蚀引起的。河谷纵剖面具有明显的下凹特性,凹度在1.40～1.65间。河道比降具有沿程变小的趋势,并遵循指数衰减关系,平均比降在1.22‰～1.85‰间。在纵向岭谷区北部,响应构造抬升作用的西强东弱的现状,河流主河道的比降具有从西向东变小的趋势。

To disclose the valley morphological characteristics and development law in The Longitudinal rang-gorge region（LRGR） , We extract 41 valley cross-section profiles by the ARCGIS9.2 base on the 1：50 000 high resolution Digital Elevation Model, and calculate the width depth ratio of the these valley cross-section profiles and in the half depths, the section area, the concavity, the index of asymmetry and some indices of the longitudinal profile characteristics. The result suggest that： the width depth ratio in the northern LRGR is small which values is between the 4 - 16, but it shows a significantly increased trend to south along the valley which is 24 at the maximum, this is due to tectonic uplift of the northern role which led to the area more out of the river under the result of incise; the cross-section concavities indicate that most of the valley is the ＂V-shape-valley＂, which means the rivers still under the process of cutting mainly in the study area; the indices of asymmetry of the valley width and valley section area reveal that these valley major is a leftist-Valley, the left gully side is gentle slope, which is due to strong southwest monsoon wind in the left valley slopside formatting precipitation zone and the right bank to form the leeward side with the weak precipitation rainfall erosion caused by the differences; the concavity of the valley longitudinal profile is between 1.40 - 1.65 with the obvious characteristics of concave ; the river gradient along the way with a small change in trend and follow the exponential relationship which is in an average 1.22% from 1.85 %v; LRGR northern part in response to tectonic uplift of the West-East weak status, the main river channel gradient from west to east with smaller trends.