Technical Note: Operational calibration and performance improvement for hydrodynamic models in data-scarce coastal areas

Abstract. In this study, we address the challenges posed by data scarcity in hydrodynamic modeling within one of the most vulnerable coastal zones in the world—the Saigon-Dongnai tidal river system in South 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 hours of measurements per month. To further improve discharge estimation from the 1D model, the coupling of a modified Manning-Strickler (MS) equation is explored. Calibration efforts reveal distinct trends in friction coefficients along the river. The introduction of indirectly measured discharge data significantly improves model performance, particularly for the Saigon River branch. Validation against independent measurements demonstrates promising results, with the coupling of the modified MS equation providing improved discharge estimates. 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 in open-access for operational use.