Sediment Reduction Effects Of Soil And Water Conservation Under The Different Scale In Jialingjiang Watershed

This paper is based on the research subject of "9th five-year and 10th five-year Key Research Programs "sediment reduction of soil and water conservation in typical small watershed of Jialingjiang River" to systematically analyze sediment reduction effects of single soil conservation measures, different combination of conservation measures and different scale watersheds by exercising basic knowledge and most advanced recent research results and by means of site investigation, model simulation, data analysis and many kinds of research methodology of sediment reduction of soil and water conservation.Through the comparison between managemed Pangdigou baisn and unmanaged Baimigou basin in the Jialingjiang baisn,by the way of the relationship of the average runoff and the sediment quantity on profile,and time runoff and sediment with the same rainfall conditions, it's showing that relationship of runoff and sediment at the managed watershed is more stable , less volatile, and small sediment; while the relationship of unmanaged Watershed is not volatile, and there is increasing sediment with runoff increasing trend. Under one rain condition, it's markedly the effect of the Soil and Water Conservation comprehensive measures to reduce of water and sand exporting cross-section of the river basin.On the research of the soil and water conservation measures to reduce sediment at the middle scale of the Jialingjiang baisn, it's drawn that in the Panlong River with comprehensive management, the total amount of reduced sand is in the combination between engineering and agricultural measures and the combination between biological and engineering, but the combination between agricultural and agricultural measures for a smaller proportion. Per unit area by the sand-effective is the combination between the biological and agricultural measures. Among the three combinations in the Mengxihe basin, the biological and agricultural is the best. At the same time this combination to reduce the sand rate at per unit area is better than the other two and the effect is very significant. According results of the rainfall-sediment model, the reducing effects of soil and water have gained apparent benefits after management measures since the 90's. Moreover, with the deepening of soil and water conservation measures, more to the latter part of the sand is going with the more obvious benefits. Research shows that the combination between biological and agricultural has significantly better than the other two.On the research of soil and water conservation measures to reduce sediment in the large-scale Jialingjiang Basin, it's conclusion that: reducing the amount of sand of the Three Gorges storage is mainly due to decreasing sediment.According to the analysis of soil and water conservation method, tributary stations was taken to the average percentage accounted for 33.8%-62.7% in the Jialingjiang basin after management compared to former from 1989 to 1998, and the soil and water conservation measures will play an increasing role in reducing erosion.Improved method on the basis of RULSE to calculate annal sediment is a new way that can provide more accurate calculations and forecasts. Jialingjiang basin basin fluctuations of simulated data and measured data has the same trend, and the relative error is less than 15% in control, so the simulation results have been satisfactory on the conditions for large-scale complex basin.At the Hilly region in Sichuan taking the method of soil and water conservation and hydrologicalmethods to analyse the same station.we can conclusion that results of hydrological way are greater than the other way; And the main stream is greater than tributary by the hydrological way,but it's opposite by the method of water and soil conservation.According to Reducing amount of the different grades river range in the Jialing baisn caused by "Changzhi" project (soil and water conservation measures), it's an average of 4.0 percent to 17.2 percent from 1989 to 1996; for the year 1996 is 7.5 percent to 31.06 percent. Effect of Soil and water conservation is becoming small with the baisn's area increaseing.Research shows that the impact of individual water and soil is very complex, the role of the major factors (rainfall, vegetation, soil, slope, etc.), has huge diversity in different conditions, so the effect is uncertainly. Therefore, in a different managemed baisn, the sediment reduction effect caused by soil and water conservation measures fluctuated the larger scope.