Study on the response of different moving speeds on storm surge in Zhejiang coastal waters

A nested tidal model for the East China Sea-Zhejiang coastal waters is built by use of MIKE21, to simulate the storm surge generated by typhoon “Chan-hom” based on Holland wind field model. The comparison of the numerical results and the field measurements shows that the simulated values are reasonable and reliable. Based on the verified model, two typhoons with extreme moving speeds (typhoon “Mary” and “Kai-tak” with low and high moving speeds, respectively) from 1949 to 2020 are simulated and analyzed. To investigate the influence of the moving speed, three different moving speeds (2.0, 1.0 and 0.5 times of the actual moving speed) are studied based on the typhoon case “Chan-hom”. The results show that (1) for the two typhoons with extreme moving speeds, although the landing intensity of low moving speed typhoon is lower than that of high moving speed typhoon, the former has a longer impact on the storm surge in the coastal waters of Zhejiang Province for low moving speed typhoon. The duration of 0.5 m or above water level increase is only 4 h for “Kai-tak”, while for “Mary” the duration of the same water level increase is 12 h. (2) for the three different moving speeds, when the moving speed is slower, the wind direction points to the shore for a longer time, which makes the water level in the area from the west of Zhoushan sea area to the Qiantang River increase due to the decrease of the moving speed. (3) The field data from Zhujiajian observing point shows that the maximum increase of the water level appears as the wind speed reaches the maximum value before landing. There is little difference in the water level increase under the three different moving speeds. At the Zhoushan offshore observing point, the water level changes periodically with the tide level. The water increase is larger at the low tide level, while it is smaller at the high tide level.