黄土丘陵沟壑区沟谷侵蚀演化的坡向差异——以晋西王家沟小流域为例

Comparison of Different Aspect of Erosion Evolvement in the Loess Hilly Area:A Case Study of Wangjiagou Catchment of Western Shanxi Province

黄土高原是世界上土壤侵蚀严重的地区之一,年土壤流失量约为22×104t,而坡沟地区的侵蚀,尤其是水沙下坡时坡度对侵蚀尤为严重,坡沟侵蚀中坡度对侵蚀的作用成为现在坡沟侵蚀研究的重要内容,野外考察和前人研究发现,坡向对坡沟侵蚀也起着重要的不可忽视的控制作用。因此,开展不同坡向土壤侵蚀的研究,对于探讨小流域不同坡向坡沟地貌侵蚀演化特征的定量研究,揭示土壤侵蚀的坡向差异和防治具有重要意义。本文通过对黄土丘陵沟壑区典型小流域王家沟大比例尺航片的解译,在GIS技术支持下,利用沟谷发育度的概念,对研究区内不同坡向的侵蚀差异进行分析研究。研究表明在黄土丘陵沟壑区坡向地貌侵蚀演化差异明显,总体上阳坡的侵蚀强度大于阴坡。各坡向侵蚀强度依次是:南偏西(SW)>东偏南(ES)>南向坡(S)>东向坡(E)>北偏东(NE)>西坡(W)。

Soil erosion in the Loess Plateau is one of the severest in the world with annual soil loess of 220, 000 tons. The studies on the erosion of slope/gullies have become one of the important issues for its great contribution to sediment yield. Studies demonstrated that sediment yield from gullied areas occupied at least 70% of that in the Loess Plateau. At present, studies on the effects of slope gradient of the gully on sediment yield have been an important issue. However, field investigation and previous studies on slope aspect also demonstrate its importance in respect of its controlling action on sediment yield. The studies on the slope aspect are helpful through quantitatively analyzing and evaluating the erosion characteristics in different aspects in loess hilly regions to prevent and control soil erosion. Presently, the application of 3S technology on soil erosion from gullied areas to quantitatively analyze its temporal and spatial changes has been an important method. In this paper, 3S technology was used based on a 1：5 000 digital orthophotomap （DOM） and digital elevation model （DEM）, by which some geomorphologic indexes, such as the line between sloping surface and gullies, slope aspect, and small sub-watersheds within Wangjiagou Watershed et al., were extracted. And the intensities of soil erosion in different aspects of the slopes were quantitatively analyzed. Results showed that slope aspect is one of the important factors influencing soil loss and the evolution of geomorphology that is sensitive to local climate. Developmental degree of gully, influenced both by waterpower and gravitational power, is a projector of the evolutional status of gullies in the respect of spatial variation, and it is an indictor of evolutional phases of the geomorphology. The evolutional phases are significantly different with higher erosion degree on sunny slope than that on shady slope for different soil temperatures, soil water contents and transpirations, soil physicochemical properties, vegetation covers, and land use patterns on different slope aspects. The erosion power of precipitation and runoff are different in different aspects, thus leading to the difference of evolutional degree of the gullied geomorphology in different aspects of the gullied-slopes. The differences of soil erosion in different slope aspects are significant, and the soil erosional intensity in the sunny aspect is much larger than that in the shady aspect. Soil erosion rate of different slope aspects in Wangjiagou Watershed adheres to the following rule： southwestslope （SW） （ eastsouthslope （ES） 〉 southslope（S） 〉 eastslope（E） 〉 northeastslop（NE） 〉 westslope（W）.