Technical note: Operational calibration and performance improvement for a 1D hydrodynamic model in a data-scarce coastal area

Abstract

In this study, we address the challenges posed by data scarcity in hydrodynamic modeling in one of the most vulnerable coastal zones in the world - the Saigon-Dongnai tidal river system in southern Vietnam. We investigate calibration strategies for a 1D hydrodynamic model using minimal in situ data obtained from an existing local monitoring program, which provides 48 h of measurements per month. Calibration using both directly measured water levels and discharge data derived from vertical velocity profiles yields the most accurate discharge estimates, with relative root mean square errors (rRMSEs) ranging from -75 % to -78 % in the Saigon River and from 23 % to 29 % in the Dongnai River, depending on tidal asymmetry. To further improve discharge estimation from the 1D model, we explore the coupling of a modified Manning-Strickler (MS) equation. Calibration results reveal distinct spatial variations in friction coefficients along the river system, highlighting the importance of localized adjustments. Incorporating this calibration technique significantly enhances model performance, reducing the discharge rRMSEs by 27 % to 44 % in the Saigon River and by 11 % to 29 % in the Dongnai River, depending on tidal asymmetry. The study underscores the complexities of calibrating hydrodynamic models in data-scarce regions, with recommendations for future modeling endeavors including incorporating more accurate upstream boundary conditions. The long time series of estimated water level and discharge provided by this study have practical implications for water resource management and decision-making in data-scarce estuarine systems and are provided open-access for operational use.