陕北洛河流域地貌演化阶段的定量分析

A quantitative analysis of the stage of geomorphologic evolution in Luohe Drainage Basin,north of Shaanxi Province

根据洛河流域地貌南北纵向区域分布规律,并参考张宗祜先生(1986)编制的"中国黄土高原地貌类型图",将洛河流域由南至北依次划分为洛川黄土塬区、甘泉一志丹黄土梁状(为主)丘陵沟壑区及吴起黄土峁状(为主)丘陵沟壑区3个地貌区。借助于GIS的空间分析功能,对洛河流域3种不同地貌绘制了Strahler曲线,采用高程积分法、信息熵法、侵蚀积分值法进行计算。结果表明:3种地貌区均属于壮年期地貌发育数量特征值范围,说明洛河流域总体的发育状态已经开始进入壮年期,但不同地貌分区的发育阶段不尽相同;洛河流域不同地貌的面积—高程积分曲线的S值大小排列顺序为:吴起黄土峁状(为主)丘陵沟壑区<洛川黄土塬区<甘泉一志丹黄土梁状(为主)丘陵沟壑区,与理论情况不相符。分析认为,这可能是由于近年来洛川黄土塬区侵蚀强度增加对洛川黄土塬区的地貌发育产生了一定的影响。

It is generally acknowledged that the evolution trend of loess landform is from loess tableland to loess ridge, and then to loess hilly. But in fact, the formation and evolution of loess landform is much more complex. The study quantitatively determined the development stage of watershed landscape by using the method of hypso- metric integral value, information entropy and integral value of erosion, which helped to understand the basic law of landscape development. First, according to the north-south longitudinal distribution regularities of loess geo- morphy in Luohe drainage basin, and referring to ＂The landscape types map of Chinese Loess Plateau＂ compiled by Zhang Zonghu in 1986, the Luohe drainage basin was divided into three landform areas from south to north in turn, that is Luochuan loess tableland, Ganquan-Zhidan loess ridge area （mainly） and Wuqi loess hill area （main- ly）. Second, with the spatial analysis function of GIS, the paper drew the Strahler curves for 3 different landform areas and made a quantitative calculation on the hypsometric integral value, information entropy and integral value of erosion in Luohe drainage basin by using the DEM data of the study area. Results showed as follows： （ 1 ） The values of three kinds of landform areas all belong to the quantity characteristic value range of maturity stage, indicating that the overall development status of Luohe drainage basin has begtm into the maturity stage. But the developmental stages of different geomorphic partition were not the same. （2） According to the topo- graphic features of Luohe drainage basin from north to south, erosion cutting intensity and the current situation of development, the total topographic feature of study area from north to south is from complex to simple. There- fore, in theory, from upstream to downstream, the S value of area-altitude integral curve for different landform of study area should be increased gradually, that is, S （loess hill）〈 S （loess ridge）〈 S （loess tableland）. This means that the geomorphology of study area in whole would be younger the farther it went downstream. But the actual calculating result showed that the size order of S value on area-altitude integral curve of different landform area was：Wuqi loess hill area （mainly） 〈 Luochuan loess tableland area 〈 Ganquan-Zhidan loess ridge area （mainly）, which is not consistent with theoretical situation. This paper thinks that this may be caused by the increase of ero- sion intensity on Luochuan loess tableland in recent years. The increase of erosion rate in modern time has a cer- tain influence on the landscape development of Luochuan loess tableland area.