Analysis On Geomorphologic Features Of The Xiyechuan Drainage Basin In The Eastern Foot Of Lvliang Mountain

The Xiyechuan drainage basin is located in the eastern foot of the middle section of Lvliang Mountain.The basin has various rock types,relatively continuous strata,various structural phenomena and all kinds of landform types.For these reasons,it is a suitable place to study the geomorphologic features of the basin.Based on the field investigation and DEM data,river length,basin area,mean width of valley,branching ratio of river system,average width between tributaries,curvature of the river,elevation of the basin,longitudinal slope of the river,slope of the basin,relief amplitude of the basin,hypsometric integral,stream profile concavity,stream length-gradient index,channel steepness index and other geomorphic indices were extracted by using Arc GIS software to recognize the geomorphologic features of the Xiyechuan basin.This thesis also analyzes how lithology of strata,tectonic movement,development time and other factors influence the evolution characteristics of landforms.The main conclusions and results are as follows:(1)The length of the 17 tributaries of Xiyechuan River is 5.80-13.85 km,the basin area is 4.01-39.48 km~2,and the mean width of the valley is 360-1480 m;the branching ratio of river system each tributary range from 3.2 to 5.4,the average width between tributaries of each tributary is 190-390 m;and the curvature of each tributary ranges from 1.04 to 1.23.The proportion of the area(slope between 0°and 25°)is 74.9%of the total basin area,which is the largest one.The area of amplitude between 75 m and 200 m accounts for the largest proportion of the total basin area(85.07%).The hypsometric integral of each sub-basin range from 0.329 to 0.521;the stream profile concavity of each tributary is higher than 1,the longitudinal profile of the river is generally concave,but the Hack profile is convex;there are steep river sections with standardized stream length-gradient index(SL/K)of 2 to 10 in all tributaries;there are river knickpoints in all tributaries,and for the tributaries on the east-west opposite side of the main stream,the steepness index of the upstream and downstream of the knickpoint is similar.(2)The distribution of elevation,slope,amplitude and hypsometric integral in Xiye-chuan basin is mainly controlled by the lithology of strata.The highest altitude of the watershed in the basin is located near the Cretaceous igneous intrusions;the second-highest watershed located in the Cambrian-Ordovician and Archean strata;the southeast side of the basin is located in the Triassic strata with the lowest watershed elevation.The distribution ratio of steep slopes and dangerous slopes(slope>35°)in each layer in the Xiyechuan Basin is:Cambrian-Ordovician(15.0%)>alkalic complex(11.1%)>Archaean(8.0%)>Triassic(5.6%)>Carboniferous-Permian(1.9%).The small relief amplitude area(relief amplitude:75-200 m)is mainly distributed on the Carboniferous-Permian and Triassic strata,while the largest relief amplitude area(relief amplitude:200-322 m)of the basin is mainly located on the Cambrian-Ordovician strata.In the sub-basins,if the distribution range of Archean and Cambrian-Ordovician is large,the hypsometric integral will be high,and the hypsometric curve will be slightly convex,on the contrary,if the distribution range of Carboniferous-Permian is large,the hypsometric integral will be high,and the hypsometric curve will be slightly concave.(3)The concavity values of all tributaries in Xiyechuan are higher than 1,and the longitudinal profile is concave,which indicates that the river erosion in this area is relatively balanced at present.For each tributary,the steepness index of the upstream of the slope-break knickpoints is higher than that in the downstream,but this figure on the east and west sides of the mainstream are similar,which indicates that the Jinzhong Basin has been continuously sinking and the Xiyechuan Basin has been uplifting since the Pliocene,but there is no significant difference in the uplifting rates of the sub-basins on the east and west sides of the Xiyechuan mainstream.(4)With the similar formation time,climate,environment,and the degree of the structural development process,within 20 km~2,the order of mean width of valley with a single formation is(from wide to narrow):Neogene-Quaternary>Cambrian-Ordovician>Car-boniferous-Permian>Triassic>Archean-Proterozoic.Under a similar climate,environment,structural condition and consistent lithology in the basin,if the formation time of the rivers is long,the branching ratio will show a downward trend,and if the formation time is short,the average width between tributaries will be large.