The use of numerical modelling to assess soil water dynamics in subsurface irrigation

ABSTRACT Knowledge of soil water dynamics is essential for establishing appropriate methods of irrigation management. Water dynamics in unsaturated soils is a complex process that can be explained by the Richards equation. As this is a non-linear differential equation, there is no analytical solution, but requires the use of the finite element method, for example, to obtain solutions, where simulations using numerical modelling make it possible to predict the the flow of water from the soil. As such, the aim of this study was to evaluate a 2D numerical model in simulating water distribution and wet bulb formation resulting from a subsurface irrigation system, in addition to validating the generated model. The Pearson correlation coefficient (r), the coefficient of determination (R2) and the root-mean-square error (RMSE) were calculated. For each treatment, both during and after irrigation, the model showed a small relative error, high values for R2 and a positive correlation with the field data. It was concluded that the model is applicable to the design and management of subsurface irrigation systems, varying the installation depth of the drip tube, the spacing between emitters and the soil moisture, giving good results for the various simulated scenarios.

摘要 土壤水动力学（soil water dynamics）知识是确立合理灌溉管理方案的核心基础。非饱和土壤中的水分运移过程极为复杂，可通过理查兹方程（Richards equation）进行理论阐释。由于该方程属于非线性微分方程，暂无解析解，需借助有限元法（finite element method）等数值方法求解；通过数值模拟（numerical modelling）可实现土壤水分流动的精准预测。鉴于此，本研究旨在评估一款二维数值模型在模拟地下灌溉系统（subsurface irrigation system）所产生的土壤水分分布与湿球（wet bulb）形成过程中的应用效果，并对所构建的模型进行验证。研究计算了皮尔逊相关系数（Pearson correlation coefficient, r）、决定系数（coefficient of determination, R²）与均方根误差（root-mean-square error, RMSE）。结果表明，在灌溉过程及灌溉结束后的各处理组中，该模型均表现出相对误差较小、决定系数取值较高的特征，且与田间实测数据呈显著正相关。最终研究结论为：该模型可应用于地下灌溉系统的设计与管理，通过调整滴灌管（drip tube）埋设深度、滴头（emitter）间距及土壤含水率等参数，在各类模拟场景下均可取得良好效果。