Channel aggradation has taken place in the tail reach of the Yellow River Estuary (YRE) because of its geologic formation and evolution since 1976. A significant process of channel degradation was caused by a sharp reduction in sediment load along the tail reach of the YRE after the operation of the Xiaolangdi Reservoir in 1999, which may influence the safety of flood control engineering. Therefore, it is necessary to investigate the fluvial processes in the tail reach of the YRE using a one-dimensional model. In this study, a one-dimensional morphodynamic model using a coupled solution was developed to simulate two hyperconcentrated flood events occurring in the tail reach of the YRE. In the model, the Saint Venant equations were improved for the hydrodynamic governing equations, including the terms of sediment concentration and bed evolution. The modified Saint Venant equations were integrated with the sediment transport equation and the equation of bed evolution. The model was firstly calibrated using the measurements in the Lijin-Xihekou reach in 2003, and then it was verified using the measurements in the Lijin-Cha3 reach in 2015. The model results for the discharges, water levels and sediment concentrations coincide with the measured data, which indicates that the developed model is suitable to simulate the hyperconcentrated flood events in the YRE. Furthermore, the effects of different cross-spacing were investigated using the same flood event in 2015. It is found that the precision of simulations decreased with the increasing of cross-spacing, and a suitable cross-sectional distance of less than 3.41 km in 2015 should be adopted when simulating the hyperconcentrated flood events in the tail reach of the YRE.