Identification Of Soil Hydraulic Property Parameters Based On The Micro-Genetic Algorithm And Simulation Of Soil Water Movement

The study of soil water movement is of great importance in agricultural production and environmental protection.Numerical solutions to mathematical models have become an indispensable tool for predicting water movement and solute transport in soil and for managing water and soil resources.The determination of soil hydraulic parameters is the key to the prediction of water movement and solute transport in soil and the application of computer models,and is also the most important factor affecting the accuracy of predictions.With the development of soil sensors and computer technology,the recent research focus has shifted to obtaining the measured values in situ at the site and inferring the unsaturated hydraulic parameters based on the measurements coupled with the numerical models and optimization algorithms for soil water movement in order to obtain more accurate predictions.In this study,a mico-Genetic algorithm(mico-GA)is combined with the basic soil water flow equation using an inverse analysis approach for soil hydraulic property parameters.The identification of soil hydraulic parameters under a field scale is carried out based on the data from experiments of ground drip and underground drip irrigation.The experiments were conducted in the Institute of Water Resources and Construction Engineering at Tarim University in China in 2012 and 2013.The following conclusions can be drawn from this study.(1)The simulation results are much improved by using the soil hydraulic property parameter values inferred by the micro-GA in this study than those by the Saxton and Wosten methods.(2)Lack of experimental data in the inverse analysis could lead to the imprecision of the simulation results.The accuracy of the inferred parameter values increases with increasing number of samples and the objective function of the inverse problem has a great influence on the results.A reasonable objective function can improve the accuracy of the simulation results.(3)The 100 generation and 5 population set in the micro-GA is a suitable genetic choice.Increasing the number of generation and population do not greatly help to improve the calculation results.(4)The simulation results could be improved by using the layed soil approach,and the number of soil layers should be determined according to the actual situation of the soil.Through the analysis of soil water movement under the drip irrigation condition by using the soil layer dependent hydraulic property parameters of two soil layers,the results show that good agreement between the measured and simulated values of soil water content is achieved.The evaluation indices of model performance are as follows:the Nash efficiency coefficient is 0.668,the mean square root error is 0.029 cm3/cm3,the mean absolute error is 0.021 cm3/cm3 and the goodness of fit is 0.689.This indicates that the inverse analysis model of soil hydraulic property parameters proposed in this study is effective and feasible,and can potentially be used in practical problems to improve the accuracy of soil water movement predicitons.