Experimental Research And Numerical Simulation Of The Soil Moisture Infiltration Property Under The Condition Of Non-sufficient Water Supply

The soil moisture infiltration process of the non-sufficient water supply is one of the important process that the nature rainfall and irrigation water to enter into soil,such as the moisture infiltration of soil under the condition of small runoff or sprinkling. Consequently, the research of the infiltration process of the non-sufficient water supply has an important value to the calculation of rainfall runoff and the determination of sprinkling irrigation technology parameter. Based on the nation natural science fund project (No.4067081) item"researches the transfer-function of soil infiltration parameter multiple non-linearity on area dimension",this paper is taken eight types soil texture form sand to clay as object of study. Adopt the method of experimental research and theoretical research and theoretical analysis and numerical simulation combination, the infiltration characteristics of non-sufficient water supply and impact factor was systemically investigated and infiltration model of non-sufficient water supply was established. It was explored the quantity relationship of model parameters of infiltration between non-sufficient water supply and sufficient water supply. The infiltration process and its modal parameters were predicted by means of multiple linearity, non-linearity and BP neural network soil transfer-function. It was realized the numerical simulation of infiltration process under the condition of non-sufficient water supply. The research finds and innovation of this paper are mainly indicated as follows: The research finds:(1) It was revealed the infiltration variation characteristics of soil moisture under the condition of non-sufficient water supply. The non-sufficient water supply infiltration process can be divided into three stages: the infiltration stage of water supply intensity control, the infiltration stage of unsaturated soil control and the infiltration stage of saturated soil control. The ponding and stable infiltration time are the demarcation point of the above three.(2) It was established the three stages model for non-sufficient water supply infiltration. Firstly, The infiltration rate of the water supply intensity controlling stage is of a constant, and its value is equal to the water supply intensity; secondly, the infiltration rate of unsaturated soil controlling stage adopts Kostiakov three parameters model; thirdly, the infiltration rate of saturated soil controlling stage equals to relative saturated infiltration coefficient.(3) The main factors influencing infiltration characteristics are the intensity of water supply, dry bulk density of the soil, the initial soil moisture and soil texture. The research was established a numerical relationship between the main influence factors and ponding time"tp", infiltration capacity, wetting front,wetting front rate,infiltration model parameters, stability infiltration time. The ponding time conforms to negative power exponent as the water supply intensity changes, and to logarithm as soil texture, soil moisture, soil structure changes.(4) It was established the relationship between infiltration model parameters of non-sufficient and sufficient water supply and realized the forecast of infiltration model parameters under the condition of non-sufficient water supply by infiltration model parameters under the condition of sufficient water supply.â‘ Non-sufficient infiltration parameter B1 is equal to water supply intensity and steady infiltration rate of the difference.â‘¡Non-sufficient infiltration of the steady infiltration rate f01 is equal to the infiltration rate f0 of sufficient water supply.â‘¢The relationship infiltration decline indexα1 andαis:α₁ = ( -0.9552+0.8355γ_d -0.1726θ_i-0.2121ω₁+1.6123ω₃+2.669R₀)α(5) In this paper, the prediction of the soil infiltration model parameters and infiltration process under the condition of non-sufficient water supply is feasible by the application of multiple-linearity, non-linearity and BP neural network soil transfer-function. The forecast error of soil transfer-function by means of multiple linearity and non-linearity is come near; its scope is from 14.9% to 43.8%. The forecast error of BP neural network by using the unlined hidden layer structure(5-10-1)is the smallest, its scope is from 6.8% to 18.8%.(6) It was established the mathematical model of the soil moisture movement under the condition of the non-sufficient water supply, and adopts the finite-difference method to simulate the infiltration process. The program carries on the simulations of the infiltration process, the moving distance of wetting front and distribution of soil moisture.Innovation:(1) This paper was established the three stages model for non-sufficient water supply infiltration.(2) Analysed systematically the effect soil texture, initial moisture, soil structure and water intensity on ponding time, the research was established numerical relationship between the main influence factors and ponding time and forecast model of ponding time and provided the theory basis for the calculation of rainfall runoff and the determination of sprinkling irrigation technology parameter.(3) Based on the experimental data with eight soils, this paper was established the relationship between infiltration model parameters of non-sufficient and sufficient water supply and provided a new method for getting infiltration model parameters under the condition of non-sufficient water supply.(4) Based on the statistics of 400 groups of experimental, this paper was realized the forecast of infiltration model parameters under the condition of non-sufficient water supply by the application of multiple linearity, non-linearity and BP neural network soil transfer-function. The forecast of BP neural network is the highest precision. This research mainly starts from the instruction of field sprinkling irrigation and the investigation of rainfall runoff, and carries out a comprehensive and pervasive study on the infiltration characteristics of non-sufficient water supply soil. It was realized the forecast of soil infiltration model parameters and infiltration process under the condition of non-sufficient water supply by the application of soil transfer-functions.However, the parameter forecast accuracy could hardly obtain precision because of the data error of observation, the experimental method and predications method. The research is needed to explore the new forecast method that makes the forecast errors controlle below 10%.