Study On Numerical Simulation Of Regulation Of Rainfall Runoff Based On WEPP Model

Two main factors of drought and water and soil erosion weigh heavily together for the economical and social development in Loess Plateau, and rainfall-runoff on slop is the main initial force for water and soil erosion. Henceforth, regulating rainfall-runoff on slop scientifically, cutting off or decreasing erosion force, utilizing water and soil resources efficiently are important approaches to solve the problems of water and soil erosion and drought. Based on the concept of regulating rainfall runoff and utilizing water and soil resources efficiently, according to calculation and verification of WEPP model combined with rainfall runoff entity scale model, simulation research on regulation of rainfall runoff on Loess Plateau slope and small sized watershed was made and several conclusions were obtained:(1) Sensitivity analysis of soil parameters. According to data of Yangling the parameters of rainfall runoff regulation station, soil albedo, initial statured hydraulic conductivity, soil critical shear stress, rill soil erosion ability, change of rill soil erosion ability are not sensitive to runoff, meanwhile, efficient hydraulic conductivity are sensitive to runoff with negative correlation. The parameters of soil albedo, initial statured hydraulic conductivity, change of rill soil erosion ability are not sensitive to sediment yield, meanwhile, parameters of soil critical shear stress, rill soil erosion ability. Besides, efficient hydraulic conductivity are also quite sensitive to sediment yield and there is a positive correlation between rill soil erosion ability and sediment yield, meanwhile, soil critical shear stress and efficient hydraulic conductivity sensitive to sediment yield negatively. According to factual condition and observation data of runoff and soil erosion of Yangling district, it was identified that efficient hydraulic conductivity to naked land was 33.8mm/h, oil critical shear stress was 4.9Pa, and rill soil erosion ability was 0.028s/m, meanwhile, the regulated three parameters were 11.2mm/h,0.49Pa和1.833s/m respectively.(2) Construction of database. According to the basic principle of WEPP model, rainfall data of runoff rainfall regulation station in Linghou, Yangling from 2003 to 2004 and layout of the district, and identified result of efficient hydraulic conductivity, soil critical shear stress and rill soil erosion ability, four database of climate, soil, slop and plant management in Yangling district that WEPP model needed was constructed. The approaches to obtain the parameters included experimental observation, formula calculation and default value of WEPP model.(3) Application of WEPP model in regulation of rainfall runoff. According to utilization residential district under the slope of 100 and 200 with enough observation data of both naked and regulated lands were verified and analyzed. The results showed that prediction of WEPP model on naked land was superior to that of land with regulated measures; the prediction on small slope was better than that of big slope; the prediction on lands with simple regulated measures was better than that with complicated regulated measures. During the factual calculation, this paper gave the modified formulas of WEPP model under different slopes and different regulation measures, which could be used as references for optimal regulation of rainfall runoff with different slopes in south Loess Plateau.(4) Response of slopes, rainfall intensity and precipitation on runoff and sediment of different regulation measures. According to analysis of water and soil under different slopes, rainfall intensity and precipitation, it showed that runoff sediment increased with the increase of slopes, rainfall intensity and precipitation under the same regulation measure, however, the regulation characteristic were different. Alfalfa performed notably in regulating sediment, which was quite efficient in decreasing sediment and inhibiting water-break in Yellow River. Relationship between regulation measures, slopes, rainfall intensity and precipitation each other were given, which made it convenient for the design and inquiry of rainfall runoff regulation plan.(5) Simulation calculation on small sized watershed of WEPP model. Based on the watershed module of WEPP model, erosion sediment yield in Yanergou watershed in Yan'an was simulated simply. The results showed that, the calculation results were quite different from the factual condition due to immaturity of model in itself and coarse generalization of slopes, ditches and sections. It suggested that segmentation generalization and calculation be applied and researched.