The Study On Impacts Of The Forest Vegetation On Runoff And Sediment In The Net Watershed Of The Loess Area In The Western Shanxi Province

In the China and foreign country, there are not the unitary result about the impact of forestry vegetation on the water and sediment. It has been one question of augmentative focus in the academic circle. The airspace heterogeneity of forestry determine that the water and sediment function of forestry is provided with different characteristics and regular in the different the nature airspace and air scale. The paper looks on net watershed of Caijiachuan in shanxi of Beijing forestry University experiment base, as object of study, and looks on runoff and sediment movement process of scale watershed constituted by single tree-forest-district of collecting water-small watershed., as enter point. The paper analyze the most interception of tree crown, the impact of the land use/ cover on the runoff and sediment, the sediment source of watershed, the impact of forest vegetation on runoff and sediment of watershed, the impact of the different scale of time and airspace on the flow process, and so on. The study provide the theory basis for the project of receding plough and returning forest and grass, the project of natural forest protection, the project of protection forest building in the loess, western of shan xi province.The main study results as follows: the average soil erosion of diversified land use: naked land 174.76 t / km2, barren grass land 68.31 t / km2, Ostryopsis davdiana Decne 2.13 t / km2, Hippophae Rhamnoides Woodlands 4.37 t / km2, china pine 18.74 t / km2, black locust 20.58t / km2, china pine and black locust 7.36 t / km2, the erosion sediment: the slope plough land > naked land > grass land > black locust > china pine > black locust and china pine > Ostryopsis davdiana Decne. The erosion sediment mainly comes from gully slope (gully head, gully bed, valley side ), Erosion modulus of valley is 1.28-2.48 times as that of the area between channels.In the rain season, the runoff deep and coefficient of land of forest covered is smaller than no forest land. The runoff deep and coefficient of rain season in the watershed of watershed of bigger forest covering is lower than the watershed of smaller forest covering, the experiment data declare: in the rain season, the runoff deep of all farm watershed is or so 5-20 times than watershed of forest covered. The forest is provided with supplying water. The experiment declare: in the lack rain season, the flow of more forest watershed is or so 9.2 times than lower forest watershed. Forest vegetation is provided with function of decreasing sediment. When the rain amount is 60.4mm, the sediment modulus of no forest watershed is 31.4 times than covered forest watershed, and the deceasing sediment benefit of forest vegetation reach to 96.81%. in the function of different rain and flow, the function of deceasing sediment is different, in the general, if rain amount is small, the flow runoff is small, then the benefit of deceasing is large. But when rain and flow is big, the benefit of deceasing is small.In the loess, the peak flow time of large area watershed is lag with small area watershed. The flow process line of large area watershed is symmetry, the flow process line is more peak. The flow process line of the small area watershed is gently, the falling process line of flow isn't coincide, with partial form, the flow process lineis single peak. In the large area watershed, due to the flex landform, the runoff model is flex, but in the small area watershed, the runoff model is single. The watershed shape and the flow speed is the main element deciding the flow process, by the flow speed formula calculating the flow line when net watershed flow process arrive at the main watershed, that is the model flow process. The data show: the reality flow process is coincide with the model flow process.The innovation point of paper: the paper looks on runoff and sediment movement process of scale watershed constituted by district of collecting water-small watershed., as enter point. According to the ecology and frame function of forest vegetation, the principal of i...