Guan'gai paishui xuebao (May 2023)
Three-dimensional Numerical Simulation of Water, Heat and Oxygen Distribution in Soil in Orchard Irrigated by Water Storage Pit
Abstract
【Objective】 Water storage pit is a technology used in arid regions in northwestern China to collect rainwater for irrigation. In this paper, we studied the three-dimensional distribution of water, heat and oxygen in soil in an orchard under water storage pit irrigation using numerical simulation. 【Method】 Water flow was based on the Richard equation and heat transfer and oxygen diffusion in soil were modelled by convection - diffusion equations. These coupled equations were solved using the COMSOL - a Multiphysics software. The model was verified against data measured from a field, and the validated model was then used to analyze the effect of the water storage pit on distribution of water, heat and oxygen in soils in the proximity of the pit. 【Result】 The three-dimensional coupled model is accurate and can reproduce the measured spatiotemporal changes in soil water, temperature and oxygen, with the RMSE for soil water, temperature and oxygen being 0.036 7, 1.609 9 and 0.013 8, respectively. The water storage pit changed the distribution of water, heat and oxygen in the pit wall greatly. As time elapsed, soil water content in the regions proximal to the pit decreased, while oxygen concentration increased. Temperatures in the pit and soil surface were mainly impacted by atmospheric temperature. Spatial water distribution was ellipsoidal around the pit. Soil water content was the highest in the proximity of the pit bottom, while oxygen concentration and temperature in this region were the lowest. The distribution of water, temperature and oxygen tended to uniformize as time elapsed, despite that temperature and oxygen are less sensitive to irrigation than soil water. Oxygen concentration decreased with the distance from the soil surface and pit wall. 【Conclusion】 Water storage pit irrigation increased the interface between soil and water, thereby affecting transport of water, heat and oxygen in the soil. Numerical simulations indicated that the dynamics of water, heat and oxygen in the soil was affected by evaporation, rainfall, atmospheric temperature, atmospheric oxygen concentration and other environmental factors.
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