Runoff And Sediment Yield Responses To Forest Vegetation At Multiple Scales On The Loess Plateau

The Loess Plateau is one of the areas that have the worse soil erosion,and it is widely considered to be the most important ways to develop large-scale water and soil conservation and comprehensive treatment which take the vegetation construction as the main body for the Loess Plateau's ecological restoration,erosion treatment,and the Yellow River's sediment control.Since the 1950s,this area have gradually develops some fixed-position observation researches on the changes of forest and vegetation,and this watershed's runoff and sediment,but there are few quantitative researches based on measured and observed date analyzing this area's vegetation changes and changes of this watershed's runoff and sediment.Therefore,from the three different scales of region,basin and slope, this paper researched the impacts that forest vegetation in Loess Plateau exerted on runoff and erosion and sediment yield,respectively.On the scale of region,according to the characteristics of regional differentiation in Loess Plateau and the scale of observed basin(the basin whose area was less than 30km~2 was small basin,and the basin whose area was more than 30 km was large and medium-sized basin),this paper collected published literatures and measured data from hydrological yearbook,discussed the quantitative relationship between the basin forest change in vegetation cover and basin runoff and sediment yield in Loess Plateau by the method of statistical analysis;On the scale of basin,this paper analyzed the impact that different vegetation types in Cai River exerted on the basin runoff and sediment by the method of field observation;On the scale of slope,this paper studied the impact that different vegetation types and structures exerted on surface runoff and sediment.The results showed that:both the medium-sized basin and small basin in Loess Plateau,with the increase of forest cover,basin runoff and sediment decrease,and the basin runoff and sediment can be controlled effectively when the forest cover reaches 40%;In typical basin,the annual runoff and runoff during the rainy season of forest basin are less than agricultural basin and river basin for farming and animal husbandry obviously.Sediment yield in each basin displays such laws as below: agricultural basin＞river basin for farming and animal husbandry＞plantation basin＞banned basin＞secondary forest basin;On the slope,runoff and sediment yield of different vegetation types displays such laws as below:Secondary forest＜bush＜robinia pseudoacacia＜shrub-grass forest＜Pine oil,and the production flow and sediment yield has better correlation relationship.On some degree, the density and canopy density of robinia pseudoacacia affects the volume of vegetation runoff and sediment.The more density and canopy density,the less runoff and sediment yield.