The study looked at how river flow and tides affect flood levels in the Han River. They found that using a steady-state flow model to determine design flood levels can lead to overestimation in tidal rivers. By using a more detailed model that considers the interaction between river flow and tides, the researchers found that the actual design flood levels tend to be lower than previously estimated. This means that structures built for flood protection may need to be designed differently to account for the joint effect of river flow and tides.