# Effect of Tide Level Change on Typhoon Waves in the Taiwan Strait and Its Adjacent Waters
## 5 Influence of High and Low Tide Levels on Typhoon Waves
### Effect of Tide Level on Wave Height  
Figure 10 shows the comparison between the simulated and measured values of the Beishuang buoy and No. 4 buoy at the time when the typhoon landfall time coincides with the highest tide level before and after the landfall of Typhoon Maria. It can be seen from the figure that the significant wave heights of all verification points first increase and then decrease with time. Additionally, the results, with or without considering the tide level, are consistent with the trend of the measured wave heights. At high tide, the maximum significant wave height of the Beishuang buoy increases by 0.34 m and decreases by 0.37 m at low tide, which means that the typhoon has a gap of 0.71 m between high and low tide (Figure 11).  
In the simulation results, the reason why the tide level of the No. 4 buoy has less influence on the wave height than the Beishuang buoy may be due to topographic factors. Beishuang buoy is closer to the land, so the water depth is smaller than that of the No. 4 buoy. The difference in water depth causes the wave height of the No. 4 buoy to be larger than that of the Beishuang buoy, so the influence of the No. 4 buoy on the wave height is less obvious than that of the Beishuang buoy.  
Figure 11 shows a comparison between the simulated and measured values of the Beishuang buoy and No. 4 buoy when the typhoon landing time coincides with the highest and lowest tide levels. It can be observed from the figure that the peak of the significant wave height appears at the time of typhoon landing, regardless of whether it is the lowest or highest tide level. The difference between the significant wave height values generated by the typhoon at high and low tide levels at the verification point is 0.5 m (Beishuang buoy) and 0.31 m (No. 4 buoy). In the case of a typhoon with the highest tide level, the  
Figure 8: Comparison of tide levels before and after shifting tide levels. (**a**) Beishuang buoy. (**b**) No. 4 buoy.  
Figure 9: Tidal height at the verification points of Typhoon Maria. (**a**) Under the influence of high tide level. (**b**) Under the influence of low tide (Translational tide level).  
significant wave height of the lowest tide level condition is lower than that of the high tide level at the peak. However, as the tide rises (7:00-10:00), significant wave heights continue to increase.  
There is a situation where the phases of the peaks of the significant wave heights are different between the Beishuang buoy and the No. 4 buoy. When the Beishuang buoy reaches the highest tide level, the No. 4 buoy still has a phase difference of \(1\) h. This is because when studying the influence of different tide levels on typhoon waves, the first consideration is the relationship between the typhoon landing time and the tide level at the landing site. Therefore, the translation of the typhoon is based on its landfall time rather than the time at which the typhoon reaches its maximum significant wave height at different verification points. When the typhoon's landfall time and the high tide level coincide, the waves generated by the typhoon are higher than in general situ  
Figure 11: Comparison of significant wave heights at the verification point after shifting the tide level (low level). (**a**) Beishuang buoy. (**b**) No. 4 buoy.  
Figure 10: The significant wave height at the verification points before and after shifting the tide level. (**a**) Beishuang (High tide level). (**b**) No. 4 (High tide level). (**c**) Beishuang (Low tide level). (**d**) No. 4 (Low tide level).  
water level height resulting from the tide level itself is combined, which has a huge impact on the safety of other marine structures such as shore breakwaters.