| It has been implemented large-scale vegetation restoration in order to prevent soil and water loss in low-mountain hilly ecological degraded region of middle-lower Yangtze River. In order to realize the effect of soil and water conservation even ecological environment which produced by vegetation restoration,study on soil erosion characters of watershed is necessary. The main intention of this paper were to realize the effect of soil and water conservation which produced by vegetation restoration in low-mountain hilly region of middle-lower Yangtze River. This paper selected Nverzhai small watershed which lies in Wuling Moutain in northwest of Hunan province as study area,analyzed some factors such as rainfall erosivity,soil erodibility(K factor) in detail. Then generalized soil erosion characters on different scale and improvment of vegetation restoration to prevent soil and water loss. Based on above,this paper simulated runoff and sediment yield combining with GIS and USLE and distributed hydrological model SWAT. Then,This paper evaluated which model can be used better in watershed. This can provide basal data for soil and water conservation of watershed in future,and also can provide experience learned and reference for soil and water conservation in future in Wuling Moutain as well as low-mountain hilly region of middle-lower Yangtze River. Main results and conclusions showed as follows:Time distribution of rainfall erosivity in watershed were not symmetrical. It was mainly concentrated from April to August. Rainfall erosivity had comparatively high fluctuation in 9 years from 2000 to 2008. Single rainfall and single rainfall erosivity,monthly rainfall and monthly rainfall erosivity,yearly rainfall and yearly rainfall erosivity were in exponential function relation. Their regressive functions can calculate corresponding rainfall erosivity. Determinative coefficient of regressive functions were 0.8605,this can gain by ways of taking monthly rainfall as variable. To calculate and analyse rainfall erosivity for long-timg,EI30 were best applicable in EI configuration. Daily rainfall precipitation model of half month periods of time R=α∑(Dj)βand non-linear and more parameters model Rj=a{1+bsin[Π(j-1)/12]} Pkc also have good applicability for evaluating rainfall erosivity.The value of soil erodibility(K factor) were between 0.2451 to 0.4623,it's variation were relative large. Soil texture of surface layer were generally coarse and the proportion of clay were little. K value which Cv was 0.1295 were in moderate variability. K value of main soil types of watershed can be calculated. Yellow earth,yellow brown earth and red earth were 0.332,0.326 and 0.318 respectively. Spatial distribution map of K value in watershed can be made by Kriging interpolation. Precision of Spatial distribution map of K value can be improved by increasing sampling density and optimizing sampling method in future.Runoff and sediment yield had largely difference on typical vegetation patterns plots in 9 years from 2000 to 2008. It greatly decreased since 2004 year and stability hereafter. Benefit from vegetation restoration to soil and water loss were evidently received since 2004. Shrub and Pingii community had preferable benefit to prevent soil and water loss. The measure of returning land for farming to forest also had better benefit. Main period of soil and water loss was April to August for distribution of runoff and sediment within year. Following with the time increment of vegetation restoration and increment of forest canopy density,the effect which rainfall factor on runoff and sediment yield were obviously increased. The representative was that correlative coefficient between rainfall factors and runoff and sediment increased obviously,and also regressive correlative coefficient of regressive functions which between rainfall factors and runoff and sediment were generally increasing except Pingii community since 2004. Sediment yield were increasing follow with the increment of runoff yield on all plots,change of Pingii community were maximal.On runoff plots of vegetation restoration,the most impacting factor to runoff and sediment yield was arbor cover. The next was capillary water holding. Slope had relatively large impacting to sediment yield. On returning land for farming to forest plots,the most impacting factor to runoff and sediment yield was slope. The next was soil infiltration speed. Shrub cover and grass cover also had great impact and their effect were the same.On watershed scale,flood season was the main time of runoff yield,flood was the main source of sediment yield. Runoff had no high fluctuation,but sediment obviously decreased since 2004. Changing extent of sediment eigenvalue were higher than rainfall and runoff eigenvalue from 2004 to 2008. Runoff increased following with the increment of rainfall,monthly runoff depth and monthly sediment yield took on positive correlation in flood season. The relativity of hydrology indexes to soil erosion were higher than rainfall indexes.The calculative equation about sediment yield of watershed can be established after 3 rainfall indexes,4 hydrology indexes and runoff coefficient Cr were selected. R2 of the equation was 0.96 by testing,this showed the equation can be used to calculate sediment yield of watershed.Soil erosion of watershed were simulated based on combining with GIS and USLE. Feeble erosion which less than 5t/(hm2·a)occupied 66.02 percent in total erosion. Forest land were feeble erosion except bamboo,this showed the benefit which forest land to prevent soil erosion. Soil erosion in elevation of 300-400m and 200-300m occupied 34.99 and 29.89 percent in total erosion respectively. This was the main area which needed to prevent soil erosion. Soil erosion between slope of 20-40o occupied 55.5 percent in total,this was also the main area which needed to prevent soil erosion. The average of yearly sediment yield was 652.37 t/(km2·a)in watershed,this was not satisfying result comparing with actual observed result and only can be used to gross estimation.Runoff and sediment yield were simulated combining with distributed hydrological model SWAT. After parameter adjustment and model test , correlative coefficient ( R2 ) and Nash-Suttclife coefficient(Ens)about simulative value of runoff depth were higher than 0.8. Relative error coefficient was only 0.004. Whole sediment yield were less than actual observed result,but it's correlative coefficient(R2) was 0.88. This showed simulative value can reflect the trend of sediment change preferable. The value of Ens was 0.78 also in precision range that model can accept. Result showed that SWAT model can simulate runoff and sediment yield preferable and had better applicability to USLE in watershed. Simulative result to runoff were better than sediment for SWATmodel.
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