Dynamic Response Process of Extreme Storm Surge in the Lingdingyang Estuary Based on the Observations at Buoy Stations: Taking Typhoon 1822 (Mangkhut) as the Example

Based on the data observed at 6 buoy stations in the Lingdingyang Estuary during Typoon Mangkhute, the dynamical characteristics in the study area are analyzed by using main tidal flux algorithm. The results show that the meteorological characteristics in the whole waters of the Lingdingyang Estuary began to be affected significantly one day before the typhoon landing, being dominated with north wind and small wind speed. During the typhoon landing, northeast by east wind was dominated, with the maximum wind speed being about 30 m/s. After the typhoon landing, southeast wind became dominant and the wind speed began to decrease gradually. During the typhoon landing, the velocities of the rising tide flow and the ebb tide flow increased significantly in the Lingdingyang Estuary and the tidal level increased continuously for about 9 hours, with the highest tidal level occurring about 2 hours later at the top of the bay than at the mouth of the bay. Before and during the typhoon landing, an ebb channel was formed in the middle waters of the west beach, and a retroactive flowing was dominated at the east four gates. When the flood discharged from upstream was encountered, the water level in the river network was caused to rise continuously, making the water level uplift about 54 cm on an average. After the typhoon landing, the power of flood continued to enhance and the wind speed decreased, causing the duration of the ebb tide in the Lingdingyang Estuary to prolong significantly. The peak value of the flow velocity shear gradient in the inner Lingdingyang Estuary occurred within a water depth range of 2 m near the bottom layer in the time period from ebb to rest. This range retracted obviously toward the riverbed during the typhoon landing. At the mouth of the bay, however, the peak value of the flow velocity shear gradient occurred mainly in the surface water in the time period from the ebb rest to the initial tide-rising. The peak value of the flow velocity shear gradient at the bottom had always been very small because of the control by the wind speed and direction at the surface of the water.