A Study On Mechanism Of Wind-water Erosion Of The Jiaolai River Valley’s Slope In Naimanqi, Inner Mongolia Province

Wind-water erosion is an important issue. Studies on the Issues concerning the soil’s wind erosion and water erosion on Ioess Plateau have been a heated topic for a long time and have made a remarkable achievement both at home and abroad. However, studies on the wind-water erosion in the arid and semi-arid region are still at the initial state, though scholars at home and abroad have devoted more energy to the study of the water-wind erosion since the21st century. Taking the middle reaches of Jiaolai River in Naimanqi, Inner Mongolia Province as an example and based on the on-the-spot investigation and observation and the laboratory data analysis, the thesis has summarized the annual change rules, calculated the erosion energy of wind erosion and water erosion, analyzed the similarities and differences between the wind-water erosion’s impact on the upwind river slope and the one downwind, and figured out the general characteristics of wind-water erosion of the river slope in the research area, which can be summarized as follows:(1) The water erosion in summer and autumn (from June to September) washes the developing gully on the slope surface and the sand material in the river valley down from the surface of valley slope, which leads to the development of the diluvial fan accumulated by sand at the foot of slope. This provides material basis for the wind erosion in winter and spring and greatly influences the local agricultural and animal husbandry production.(2) The wind erosion in winter and spring (from March to May) blows the sandy materials on the upwind valley’s slope to the foot of slope, which gives rise to the accumulation of those sandy materials at the foot of the slope and the deflation of smaller grains of sand to the riverbed. Sandy materials on the riverbed are blown to the foot of the downwind river valley’s slope and those on the downwind river valley’s slope extend to the river bank under the impact of wind. Then, those smaller grains of sand form the blowing sand, devour the river bank and change into a typical dune complex.(3) From the erosion energy of wind erosion and water erosion, it is noticeable that the research area is a wind-water erosion ecotone in which wind erosion is the primary erosion, while water erosion is secondary one. During the active period of wind erosion, the wind erosion energy can reach250.79J-d/m2, while during the active period of water erosion, the water erosion energy is only48.95J-d/m2.(4) Due to the wind erosion’s and the water erosion’s different impact on both sides of Jiaolai River, the topographic feature of upwind valley’s slope and downwind river valley’s slope is different. As the direction of wind erosion and water erosion on the upwind valley’s slope is identical, a lot of sandy materials coming from the top of the slope are accumulated at the foot of slope and form a smooth gentle slope. However, the direction of wind erosion and water erosion on the upwind valley’s slope is different, and water erosion makes sandy materials on the surface of the slope accumulate at the foot of slope which are blown to the back of the valley by the wind erosion. Therefore, only when the energy of wind erosion and water erosion reaches equilibrium, the development rate of the river valley’s slope is minimized and the wind erosion energy is much larger than that of water erosion can the downwind river valley’s slope develop into the concave slope.(5) Wind erosion makes soil on the windward side into fragmental and causes the accumulation of sand on the leeward side. At the same time, a large number of sandy materials washed from the rain channel spread rapidly under the influence of wind, which leads to the rapid development of sandy land and the gradual devouring of farmland vegetation in the downwind river valley.(6) As in the upwind valley, the protection forest is intensive, the vegetation coverage rate is high, the development of sand dunes is slow and some sand dunes even stop developing, the erosion rate of the upwind valley is much lower than that of the downwind valley. Under the influence of the northwest wind, the erosion of rain and the trample of human beings and animals, lots of superficial clay are eroded and sandy materials increase rapidly. Jiaolai River has been cut off for many years, which brings down the water erosion energy and reduces the impact of wind-water erosion. In addition, the undercutting of river is a significant component of wind-water erosion, which in the long turn will make the Jiaolai River valley’s slope gradually change into a gentle slope and become a widespread dune complex.