黄土高原典型区沟谷分布谐波分析

为了研究黄土高原地形起伏的周期性,从而探索支沟沟谷分布规律,为黄土高原的土壤侵蚀评估提出新的思路。该文以甘肃西峰、山西吉县、陕西安塞、宁夏固原为研究区尝试利用谐波分析和周期图分析的方法研究黄土高原不同类型区沟谷分布规律。结果表明,黄土高原不同类型区主沟沟谷的周期大小有明显不同,总体来看,高原沟壑区>过度地区>丘陵沟壑区;黄土高原支沟周期主要分布在400～800m,其周期个数占总周期数的97.5%。对4个研究区的支沟沟谷周期数据进行t检验,结果表明甘肃西峰、陕西安塞、山西吉县相互之间周期均值差异均无显著性(P>0.05);宁夏固原与陕西安塞、山西吉县、甘肃西峰侵蚀支沟分布周期均值双尾检验概率P值均小于0.01,故可认为均值差异极显著。提取不同类型区大于5°坡度的平均坡度分析发现,研究区平均坡度的大小关系为:甘肃西峰>山西吉县>陕西安塞>宁夏固原,支沟沟谷的平均分布周期随平均坡度的增加而不断减小,说明区域平均坡度的大小直接影响着黄土高原支沟的形成。

Harmonic analysis of valley distribution in typical areas of Loess Plateau

In order to study the topographic periodicity of the Loess Plateau, and to explore the distribution law of tributary valleys, so as to explore a new method for assessment of the Loess Plateau soil erosion, the paper briefly describes basic principles of harmonic analysis and periodgram analysis. Taking Xifeng in Gansu、Jixian in Shanxi、Ansai in Shaanxi、Guyuan in Ningxia as study areas, the valley distribution in the Loess Plateau was studied based on harmonic analysis and periodgram analysis. The results indicated that in the Loess Plateau regions of different types, the period of main channel differed significantly. Generally speaking, the period of the gully region of loess plateau was greater than the transitional region, and the period of the transitional region was greater than the hill and gully area of Loess Plateau; The period of branch gully in the Loess Plateau mainly ranged from 400 to 800 m, which accounted for 97.5% of the overall periods. Based on t-test of the period of branch gully in four different research areas, the results showed that the mean periods of Xifeng、Jixian and Ansai had no significant difference (P>0.05), while in the two side test,all the probability of mean period of branch gully in Guyuan、Xifeng、Jixian and Ansai was less than 0.01 (P<0.01), so it can be considered that the difference was extremely significant. On analyzing the average terrain slope greater than 5° in the regions of different types, it was found that Xifeng in Gansu is steeper than Jixian in Shanxi, and Jixian in Shanxi is steeper than Ansai in Shaanxi, which is steeper than Guyuan in Ningxia. It was also found that the average period of branch gully decreased continuously with the increasing of the average slope. Therefore, it can be concluded that the average terrain slope can directly affect the formation of branch gully in the Loess Plateau.