| The soil erosion in karst rocky desertification area has become an extremely serious ecological disaster in Southwest China,which restricts the development of local society and economy.The model of soil erosion is the frontiers of soil erosion,and it is one of the effective methods for soil erosion analysis.This research takes Guanling Karst rocky desertification area of Xiangle small watershed as the research object,through the monitoring data collection,field investigation and laboratory experiment,establishment model WEPP of four database of vegetation,soil,meteorological and topographic to predict soil and water erosion.Simulating runoff and sediment yield of time rainfall in two dimmeions of small watershed and slope,establishing the optimal WEPP model parameters through the choice of parameter optimization,evaluating the WEPP model’s applicability in the area,and doing the scenario simulation.The following main conclusions:(1)The runoff and sediment yield of time rainfall on grassland,bare rock grassland,and cultivated land + woodland slope simulated by the WEPP model can achieve the ideal effect,achieving the standard of class C,WEPP model is suitable for simulating in the region with the types of slope surface.Rainfall <50 mm,Nash coefficient Ens of runoff and sediment yield on the grassland,bare rock grassland and arable land + woodland slope are above 0.72 and 0.50,R2 above are 0.74 and 0.67,and the optimal hydraulic conductivity coefficient are 1.40 mm/hr,1.70mm/hr and 1.80 mm/hr,the best rill erosion are 1.80×107 kg·s/m4,3.50×107 kg·s/m4,6.00×107kg·s/m4.Rainfall ≧50 mm,Nash coefficient Ens of runoff and sediment yield on the grassland,bare rock grassland and arable land + woodland slope are above 0.65 and 0.53,R2 above are 0.81 and 0.55,and the optimal hydraulic conductivity coefficient are 10.00 mm/hr,15.00 mm/hr and18.00 mm/hr,the best rill erosion are 3.80×106 kg·s/m4,7.00×106 kg·s/m4,1.25×107 kg·s/m4.(2)In the scene of simulating on the slope of small watershed,rainfall < 50 mm,the runoff of cultivated land and forest land are 4.64 times and 0.16 time of bare rock grassland respectively,the sediment yield of of cultivated land and forest land are 3.98 times and 0.21 times bare rock grassland respectively.Rainfall ≧ 50 mm,the runoff of cultivated land and forest land are 4.31 times and 0.48 times of bare rock grassland respectively,the sediment yield of of cultivated land and forest land are 5.28 times and 5.28 times bare rock grassland respectively.(3)The tendency of the simulated values and measured values of the runoff and sediment yield of time rainfall from small watershed,are consistent,the results of simulating can achieve the standard C,WEPP model is suitable for simulating on the same kind of river basin scale in the region.The coefficient of Nash Ens and linear regression coefficient R2 of Runoff are above 0.95,relative error Re within 10.20%.The correlation between measured and simulated values ofsediment is very good,but the difference is very big,comparing the soil erosion modulus with non karst karst region.But it can achieve good effect that sediment yield multiplied by the coefficient1/8,and the coefficient of Nash Ens of Runoff is above 0.90,relative error Re within-19.63%.(4)In the scene of simulating in the small watershed,the runoff and sediment yield,which were simulated in different scenarios of small watershed,has the same change trend,but with big different variations between increase and decrease.The values of runoff simulated in the time of rainfall of grassland and farmland are higher than current situation values,the values of runoff simulated in the time of rainfall of shrub and forest are lower than current situation values,in the total,farmland > grassland >current situation > shrub > woodland.The values of sediment yield simulated in the time of rainfall of grassland,shrubs,woodland are below the current situation,the value of sediment yield simulated in the time of rainfall of farmland is higher than the current situation,in terms of total,farmland > current situation > grassland > shrub > woodland,The grass can increase the flow rate,reduce the yield of sand,and have the effect of "increase the flow and reduce the sand".The differences of runoff and sediment yield in the different situation simulation with big rain are great,and rainfall is little,the difference is small,even no difference.(5)In the case that simulating farmland,grassland,and shrub became woodland,the runoff was reduced by 63.72 mm,29.87 mm and 13.21 mm respectively,and the amount of sand produced is reduced by 113.12 t/km2,28.71 t/km2,and 21.60 t/km2.In the case that simulating grassland,shrub and woodland became farmland,the runoff was increased by 13.58 mm,32.24 mm and 106.97 mm respectively,and the amount of sand produced is increased by 36.66 t/km2,64.85 t/km2,165.66 t/km2. |
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