The agricultural drainage engineering community is steadily shifting the design of subsurface drainage systems from the experience-based design approach to the simulation-based design approach. As with any design problem, two challenges are faced; firstly, how to determine all the input data required by the simulation model, and secondly to, a priori, anticipate what the performance of the designed system will be. This study sought to evaluate the performance of the WaSim model to simulate fluctuating water table depths (WTD), and drainage discharges (DD) in KwaZulu-Natal Province, South Africa. Saturated hydraulic conductivity (K_sat), which is an input to the WaSim model, was estimated by the Rosetta computer program, based on soil particle size distribution data, bulk density, and soil water retention characteristics at pressure heads of – 33 and – 1500 kPa. performance of the WaSim model was statistically assessed using the coefficient of determination (R²), coefficient of residual mass (CRM), mean absolute error (MAE), mean percent error (MPE), and the nash–sutcliffe efficiency (NSE). during the validation period, the WaSim model predicted WTDs with R², CRM, MAE, MPE, and NSE of 0.86, 0.003, 4.9 cm, 6.0%, and 0.98, respectively. In the same validation period, the model predicted DDs with R², CRM, MAE, MPE, and NSE of 0.57, 0.002, 0.30 mm day⁻¹,11%, and 0.76, respectively. These results suggest that the use of Rosetta-estimated K_sat data as inputs to the WaSim model compromised its accuracy and applicability as a subsurface drainage design tool. Owing to the relatively low R² value of 0.57, and that the WaSim model was empirically developed, we recommend further improvement on the calibration of the model for it to be suitable for application under the prevailing conditions. Also, in the absence of other means of determining K_sat, we caution the use of Rosetta-estimated K_sat data as inputs to the WaSim model for the design and analysis of subsurface drainage systems in KwaZulu-Natal Province, South Africa.

农业排水工程界正在稳步将地下排水系统的设计从基于经验的设计方法转变为基于模拟的设计方法。与任何设计问题一样，面临两个挑战；首先，如何确定仿真模型所需的所有输入数据，其次，先验地预测所设计系统的性能。本研究旨在评估 WaSim 模型的性能，以模拟南非夸祖鲁-纳塔尔省的波动地下水位深度 (WTD) 和排水量 (DD)。饱和导水率 ( K _sat)，这是 WaSim 模型的输入，由 Rosetta 计算机程序根据 – 33 和 – 1500 kPa 压头下的土壤粒度分布数据、容重和土壤保水特性进行估计。使用决定系数 ( R ² )、剩余质量系数 (CRM)、平均绝对误差 (MAE)、平均百分比误差 (MPE) 和纳什-萨克利夫效率 (NSE) 对 WaSim 模型的性能进行统计评估。在验证期间，WaSim 模型预测 WTDs 的R ²、CRM、MAE、MPE 和 NSE 分别为 0.86、0.003、4.9 cm、6.0% 和 0.98。在同一验证期内，该模型预测的 DDs 与R ²、CRM、MAE、MPE 和 NSE 分别为 0.57、0.002、0.30 mm day^-1 ,11% 和 0.76，分别。这些结果表明，使用 Rosetta 估计的K _sat数据作为 WaSim 模型的输入会损害其作为地下排水设计工具的准确性和适用性。由于相对较低的R ²值为 0.57，并且 WaSim 模型是根据经验开发的，我们建议进一步改进模型的校准，使其适用于当前条件下的应用。此外，在没有其他方法确定K _sat的情况下，我们警告使用 Rosetta 估计的K _sat数据作为 WaSim 模型的输入，用于设计和分析南非夸祖鲁-纳塔尔省的地下排水系统。