贺兰山水系流域数值地貌特征及其构造指示意义

Geomorphic indices of the river and drainage in Helan Mountain and its indication to tectonics

基于Arcgis9.3与ASTER GDEM数据,提取了贺兰山两侧主要水系及其流域边界,根据河流及流域指标提取河流纵剖面、流域的Strahler曲线,并计算其面积高度积分值(Hypsometric Interg-ral)、河流纵剖面的凹度值(Concavity)。通过HI值、凹度值同河流落差、河流长度、流域面积之间相关性分析发现,后3种地貌参数与HI值、凹度值间的相关性较差。对比分析贺兰山两侧河流HI值及凹度值发现:贺兰山东侧北段活动性大于南段,西侧构造活动性分布规律不明显。结合9条河流所处流域的Strahler曲线、河流纵剖面形态和HI值、凹度值分析发现:汝箕沟及其以北贺兰山地区处于地形演化的老年期,汝箕沟以南贺兰山段处于均衡调整的壮年期。

Watershed terrain and the relationship between drainage tectonic and erosion are one of the core content of geomorphology.The Helan Mountains area locates in the west edge of the Ordos,and it is a hinge area which links the western and eastern different geotectonic units of the north of China.Research on river system and watershed area in the Helan Mountains can help us to construct in-depth understanding of river and landscape evolution in tectonic movement active regions.Many authors have studied the characteristics of the tectonic and climate of the Helan Mountains,But for rivers,the especially quantitative analysis of river morphology is relatively rare.Hypsometric integral is a relief variable that is widely used to measure the degree ofuvial landscape erosion and describes the distribution of elevations across the drainage basin area.It is a powerful tool to tell apart the tectonically active and inactive areas.We choose hypsometric integral and stream profile concavity to study the tectonic activity and evolution of the landforms in the Helan Mountains.The drainage network and drainage basins in the Helan Mountains and the hypsometric integral and concavity of the river profile have been extracted from GDEM data based on software Arcgis 9.3.There is little correlation between hypsometric integral,as well as concavity and river fall,river length,drainage area,in other words,the latter three parameters have little effect on hypsometric integral and concavity.Comparative analysis on hypsometric integral and concavity of the mountains'eastern and western segments,the HI values of the eastern Helan Mountains gradually decrease from the north to the south,and this infers that the tectonic activity is relatively higher in the northern part of eastern foothills than in their southern part;the average HI value in the eastern part is 0.46,and 0.40 in the western one,meaning that the tectonic activity of the eastern part is higher than that of the western one.The concavity values of R2,R3,and R5 are greater than that of R6,R7 and R8;and the tectonic activity of the eastern part is lower than that of western part.The concavity values gradually increase from the north to the south in the eastern and western parts of the Helan Mountains,meaning their northern part being with lower tectonic activity than their southern part.Obviously,this inconsistency may indicate that many problems still exist in the specific quantitative analysis of different basins when HI and Concavity are applied.Repeated studies through other indicators in the same area are needed.Statistical analysis of HI values of different basins shows that HI values could be divided into three categories: <0.35,0.35-0.60 and >0.60,which correspond to the geomorphic evolution of the topography of old,mature and youth age,respectively.The HI values indicate that,there is no basins in youth age,most drainage basins are in mature stage,R1、R6 are in old stage.In the point of Concavity value,all 9 rivers are greater than 1,meaning that the main work of these rivers is lateral broadening.Our main conclusion is that for the northern region of Rujigou,the topography is in old age yet,the topography in the southern Rujigou is in mature stage.