The Study Of Soil Erosion From Sloping Farmland In Three Gorges Reservoir Area

Soil erosion in slope cultivated lands is the main source of sediment in Three Gorges Reservoir area, in order to study the mechanism of soil loss in Three Gorges Reservoir area. This paper on the base of the research on climatic factors, taking of samples, observation and measurement, analysis indoors, and mathematic analysis, the further research on the main factors and mechanism of soil loss in Three Gorges Reservoir Area is also suggested, the major results is followed:(1) in slope cultivated lands of purple and yellow soil, the types of slop surface runoff all belong to infiltration excess runoff, coincidence the process of Soil Water Infiltration in Holden model, Producing Law of runoff is followed:When t≤t_p, f(t) = i(t); i(t) = ∫i(t)dt。When t>t_p, f(t) = I(t)/t: I(t)=∫i(t)dt-Q(t)。t: rainfall duration; t_p: duration of producing runoff; I(t): infiltration rate(mm/min); I(t) cumulative infiltration capacity(mm); R(t): rainfall rate (mm/min); Q, (t): cumulative runoff capacity.(2) Effects of different soil types on precipitation infiltrationHorton formula is used to analysis a numerical rainfall infiltration processes in rainfall simulation experiment, the result is followed.The regressions function of yellow soil:f = 0.6088 + 0.2742exp[-0.051(t - t_p )] (r = 0.9001)The regressions function of purple soil: f = 0.7932 + 0.0898exp[-0.049(t -t_p)] (r = -0.9129**)。 f: soil permeation rate, (mm/min);t: accumulative total time from rainfall,(min); tp: duration of producing runoff.(3) Regression model of runoff formation in slopeUsing the linear regression method to establish the linear regression model of runoff formation in the slope of purple and yellow soil respectively.purple soil: Q₁ = -0.047 + 0.0024s + 0.008i;yellow soil: Q₂ = -0.051 + 0.00235 + 0.009i。Q1,Q2: volume runoff in 1m² of purple and yellow soil (m³) ;s: slope degree, (°); i:rainfall rate, (mm/min).(4) The Laws of runoff producingr in slope are as follow:Be of the same slope degree, the same rainfall rate, and the same cropping, the grain composition of purple soil before and after rainfall occurrence is noticeably different.Be of different slope degree, different rainfall rate, and different cropping, the grain composition of purple soil before and after rainfall occurrence is not noticeably different. It shows he grain composition of purple soil before and after rainfall occurrence is very little affected by different slope degree, different rainfall rate, and different cropping.Rainfall duration have important effect on grain composition in runoff, different rainfall rate also have important effect on grain composition in runoff.(5) Effects of runoff on sediment production in sloping landsBe of the same precipitation and slope degree, sediment content in water flows gradually rising after producing runoff, until reach the peak, and then gradually lowering and tending toward equilibrium, the time of the peak connect with rainfall rate, the bigger the rainfall rate, the time the earlier.Through regression analysis to dates of sediment model, establish forecast equation of sediment production in sloping lands of purple and yellow soil:purple soil: S = 0.18 + 0.021s + 0.05i + 0.141si;yellow soil: S = -0.391 + 0.039s + 0.071i + 0.089si.S: soil erosion amount in 1 m², (kg/m²) ; s: degree, (°);i: average rainfall rate (mm/min).(6) Mechanism of soil nutrient loss in slope The Nutrient Content of purple and yellow soil is different before and after rainfall occurrence. Total quantity of soil nutrient loss in runoff has correlation with runoff amount, the regression equations is followed:E=e_SS + e_RQ。E: the amount of soil nutrient loss of slope land (g/m²); e_S: The Nutrient Content in the lost sediment (g/kg); S: sediment of slope land (kg/m²); e_k: The Nutrient Content in runoff (g/kg); Q: runoff of slope land (kg/m²).78% of slope cultivated lands in Three Gorges Reservoir Area is the main source of reservoir sediment, therefore greatly strengthen the study on mechanism of soil loss of slope cultivated lands, shoulder heavy responsibilities, compound planting model is the best method to harness soil loss equation of cultivated slope land.