Tidal waves in estuaries change in size and shape due to factors like river flow and friction. A study using a simplified model found that higher river flow can affect a specific type of tidal wave called M4 overtide. The M4 overtide gets weaker in some parts of the estuary but stronger in others as the river flow increases. The study shows that the river flow influences the M4 overtide by changing the bottom stress, which affects how energy is transferred between different types of tides. These findings help us understand how rivers and tides interact in estuaries, which can be important for predicting flooding and sediment movement in these areas.