Research On Soil Loss Equation Of ChongQing City Based On Reversied Univers Soil Loss Equation (RUSLE)

ChongQing is located in the dominant position of Three Gorges reservoir area, which topography is mainly low hilly. In these area the soil erosion modulus is as high as 3798～9831t/ (km2.a), and sloping land erosion is the main sediment source for soil erosion. The soil erosion related to the sustainable development of agricultural ecological environment in ChongQing City and the security and stability of the Three Gorges Reservoir. Soil erosion prediction model is an effective method to predict soil erosion, soil and water conservation planning. It is necessary to establish calculation mode for soil loss prediction in ChongQing region based on the law research of soil erosion in the purple soil slope.Using the methods of simulated rainfall experiment, standard runoff plots observation, soil physical and chemical properties analysis and literature data analysis, and based on the sloping erosion process characteristics analysis in the purple hilly region of ChongQing, this paper researches the values of regional parameters with systematic to the rainfall erosivity factor (R), erodibility factor (K), topographic factors (LS), vegetation cover and management factor (C), and water conservation measures factor (P), and establishes the soil loss prediction equation based on RUSLE in ChongQing region, designs the ChongQing soil loss equation programming model using VC ++ programming language, and analyzes the soil erosion modulus and slope thickness in Municipal distribution of rainfall erosivity, different land use types and different conditions of soil and water conservation measures in ChongQing region. The main results are as follows:(1)Detachment rate Dr of slop erosion is negatively correlated with rainfall duration, rainfall, slope of initial water content and slope length, and it is positively correlation with rainfall intensity, runoff, sediment yield and runoff sediment concentration. Detachment rate has the significant linear regression relationship with total of sediment yield, runoff sediment concentration and the slope gradient. In topographic factors, slope is more significant with detachment rate of slop erosion, and it can be well fitted using quadratic function between slop and detachment rate. There is a critical slope to detachment rate of surface soil erosion, and the critical gradient is 23.4°. With the slope length increases, runoff increases rapidly, and the runoff in 4m slope length is roughly 2.7 times the length of slope 2 m. Under 20.6°gradient, with the slope increases, runoff increases close to a straight-line relationship between the slop. In 20.6°the flow rate increased to maximum capacity. The sediment yield of 4m length slope is about 1.3 times comparing with the 2 m length slop. In different conditions of slope length, the relationship between slop gradient and intensity of soil loss will be fit for the quadratic relationship. The critical slope gradient of erosion in purple soil of arable land is 22°.(2) The rate of surface gravel coverage before the precipitation, after 3 times precipitation, after 6 times precipitation ware 1.5%,2.4% and 12.2% respective. Surface gravel cover has the positive correlation with the accumulation of sediment yield. It is more significant degree that the later rains sediment yield caused gravel during slope land erosion in the same conditions. In the period of prophase rainfall,the loss thickness of soil layer caused by soil erosion increases rapidly with the rainfall increased, and the rise rate of loss thickness of soil layer which caused by rainfall increased reduce after 4 times rainfall. There is a good linear relationship between cumulative rainfall and loss thickness of soil layer at different topography factors Combination.(3) The soil surface crust in different rainfall exist the dynamic development process of "no crust→weak crust→hard crust→Weak crust→new crust leather". The soil surface crust was not significant influence to soil splash erosion in the continuous rainfall during the different storms, but there was a dynamic response between soil surface crust and runoff. The degree of influence to runoff by soil surface crust has increased with continuous experiment of simulated rainfall. There are different impact relation ship between soil surface crust and slope erosion. It has a same trend between soil surface crust strength and slope erosion at the former of four times rainfall, and soil surface crust showed the inhibitory to slope erosion after four times rainfall experiment.(4)ChongQing soil loss equation use the basic structure of RUSLE model. This paper use model prediction uncertainty factor Ef to evaluation the accuracy of the model prediction result, and the Ef value is 0.802. It is indicating that ChongQing soil loss equation has a more reasonable parameter values system, and the model can be applied to the soil loss prediction, soil erosion investigation and soil and water conservation planning in ChongQing area. Parameters sensitivity of the CQSLE in order is:annual rainfall> vegetation cover and management factor> soil and water conservation measures factor> percentage of very fine sand>slope> soil infiltration coefficient>percentage of clay>soil structure coefficient>slope length>organic matter content> percentage of sand content in soil, and the main parameters of the sensitivity in degree were moderately sensitive.(5)The rainfall erosivity of ChongQing area are between in 3500～1500 MJ·mm·hm-2·h-1·a-1, and its mainly distribute at April to October._Soil and Water Conservation patterns in different erodibility size:ladder flat mode> cross slope farming patterns> Lawn mode> downslope tillage systems> Water Conservation forest mode> of economic fruit forest mode> hedgerow> Forest pattern, different sweet potato cropping patterns, the alfalfa field, mulberry soil erodibility is greater than 0.042, maize+sweet potato, plum, the pine low soil erodibility were 0.028,0.026,0.024, vegetable, maize, grassland, woodland loquat poplar trees, and other modes of soil erodibility K values distributed between 0.031～0.036. The annual C value of wheat in Chongqing is 0.4345, and the ipomoea batata is 0.3864, the ratio of C value of wheat and ipomoea batata is 0.4037. P value of contour tillage is in the ranges of 0.48～0.92. and that of contour tillage of plant hedg is in the ranges of 0.54～0.77, Average P values are 0.708 and 0.661. P values of tillage treatments is in the ranges of 0.18～0.763 and 0.126～0.730 in different ecological restorations and grass measures, mainly concentrated within the 0.3～0.5.(6) According to the needs of soil erosion prediction model for the construction of soil and water conservation and ecological environment in ChongQing region, and to the center of the needs of the user computing and analysis of the amount soil loss, we programde procedures of ChongQing soil loss equation model (CQSLE), and this model can achieve calculation soil loss in a specific ChongQing land-use scenarios.(7) It has a high consistency between soil erosion and rainfall erosivity distribution. The amount of soil loss in southeast ChongQing (high values of rainfall erosivity) is 37.01 t/(hm2 a), and it is 27.49 t/(hm2 a) in western ChongQing (low rainfall erosivity District). The average amount of soil erosion modulus in sloping land is 30.72 t/(hm2 a), which is much larger than the forest land (0.30 t /(hm2 a)) and grass land (1.66 t/(hm2 a)).The size order of the soil erosion modulus in different cropping patterns is:Wheat+sweet potato> sweet potato to> wheat> com> corn/sweet potato> wheat+maize/sweet potato. The forest-grass measures have the best control effect of soil erosion in three major soil conservation measures in ChongQing area, and the following is engineering measures. The best effect measures in agriculture measures is Grain, economic crops-fruit ridge measures (the soil erosion modulus is 8.48 t/(hm2 a), and the following is the no-tillage measures (erosion modulus is 8.75 t/(hm2 a), and the worst is cross slope cultivation measures (erosion modulus is 20.64 t/(hm2 a).(8) The average loss thickness of soil layer in bare sloping land is 4.479mm which hasn't any defend measures, and greater than annual thickness of pedogenic. The annual loss thickness of soil layer on downslope arable land with crop cover, cross farmland with crop cover, farmland with hedgerows, the level of terrace land with cover crops, woodland and grassland were 1.931,0.728, 0.533,0.041,0.001 and 0.079 mm, and both of them are less than thickness of pedogenic. The loss thickness of soil layer in different zones of ChongQing:Southeast of ChongQing>Central part of ChongQing>Northeast of ChongQing>Major city of ChongQing>Western part of ChongQing.