Hydraulic river model calibration and validation for comprehensive hydrograph simulation: Evaluating accuracy across discharge ranges

This study evaluates the performance of a hydraulic model across discharge ranges, including those outside the calibrated range, to assess its robustness beyond calibration conditions. Using the Differential Split-Sample Test (DSST), we systematically assessed the model’s ability to simulate water levels across different discharge ranges while calibrated for specific ranges. The application of the DSST method to hydraulic models introduces a structured framework for evaluating model performance across a wider range of discharge conditions, offering clearer insights into the role of discharge-related roughness calibration. A case study on a lowland river in the Netherlands, employing a two-dimensional depth-averaged (2D) hydraulic model, revealed both the strengths and limitations of 2D simulations with shallow water equations, especially under extreme flow conditions. The findings show that calibrating for moderate discharges yields reliable results for other moderate flows and performs better for extreme low discharges than for high ones. Calibration for low or moderate flows always results in Y-KGE values larger than 0.9 and a MAE less than 10 cm for all moderate and low flows. However, this is not the case for high flows in the validation. While model accuracy declines at the extremes high flows, this approach ensures reliable performance across a broad range of hydraulic conditions and highlights the need for gradual calibration for extreme high flows due to the significant variations in accuracy. Consequently, this approach aids water managers in optimizing resource allocation, predicting and mitigating flood risks, and supply across diverse discharge scenarios.