Prediction And Research Of Water-Soil Environment Effect Under Light-Saline Water Irrigation Based On Visual MODFLOW And SWAP Coupling Model In Arid Area

Because of the shortage of fresh water and the competition of the industry, it increasingly depends on the pool-quality water (saline water or city sewage) in agriculture produce. The environment problems caused by the pool-quality water utilization has becomed the hot topic and forward position task in the research field, and the soil-water environment is the most activest component of the irrigation agriculture and is the core of governing the salinization. This research reveals the laws that saline water irrigation influeces the crop physiological indicator, underground water level, underground water quality and soil salt, etc. This research also predicts and evaluates the effect of soil-water environment caused by the light saline water irrigation in the arid and semi-arid region. It is important and meanful for the Hetao Irrigaiton District where the water resource is decreasing, and it can provide consultation for similar districts, as well. The research includes the three-dimensional groundwater movement and solute transport simulation system Visual MODFLOW that has gained the worldwide approval, and the SWAP model which simulates soil water movement, solute and heat transport in the Soil-Atmosphere-Plant System in this paper. Thus the saturated and unsaturated zones construct one whole system. The soil water environment effect introduced by light saline water irrigation is forecasted and researched, and the feasibility of light saline water utilization is proved fully. The VMOD model and SWAP model are firstly coupled and used in this paper. Until now, VMOD is mainly used in the groundwater movement simulation, and it is few used to simulate groundwater quality. This paper tries to apply the MT3DMS model of VMOD into forecasting groundwater quality and to point out the limitations. SWAP is one dimensional vertical water salt movement model, and there are different SWAP models in different conditions. In this paper, the Geostatistics is used to analyze the spatial construction of soil water salt information in the researching district. Based on the analyzing results, the research district is divided into two small parts. Therefore the Geostatistics theory and the SWAP model are coupled successfully, where it avoiding the subjectivity of using one SWAP model in one district. Successive field irrigation experiments, special and conventional observations, the related parameters observed in the field and the boundary conditions determined, all these above provide the solid basis for applying the VMOD and SWAP system into this research. In the research of crop resistance capacity to salt, it is found that the soil salinity increases obviously in the definite deep zone when the salt concentration of irrigation water reaches the critical value. This critical value is basically coincided with the salt concentration of irrigation water that restrains the crop growing and decreases the crop yield. Different crops have the different critical concentrations of irrigation water. In the research, it is also found that the resistance capacity to salt is enhanced through leaching irrigation. Leaching irrigation can leach salt into deep layer while drain salinity from soil layer. As the result, the soil salinity in the root area is decreased. By establishing the correlation between yield and salt concentration of irrigation water, the thresholds of salt tolerance for three main crops are determined. The salt tolerance threshold of wheat in two kinds of irrigating quota is 4.5g/l. In the normal quota, the salt tolerance threshold of maize is 3g/l, and it is 5g/l for sunflower. In the leaching quota, the salt tolerance threshold of maize is 3.5g/l, and it is 7g/l for sunflower. The predicted value is basically accordante with the factual value. The result predicted by the method of average year is accordante with the result predicted by the method of considering time array. The method of average year is a simpler method in predicting tendency. The simulated results show that the salt in the high mineral zones...