| Laotieshan channel which is located in the east of Bohai Sea, is one of the main channels where sea water flows in and out of Bohai Sea. The tidal geomorphology system of Liaodong Shoal shaped by strong current is composed of Liaodong Shoal, Bozhong Shoal and Laotieshan Channel. A mathematical model of tidal current, erosion and deposition in the North Yellow Sea and Bohai Sea is established based on the analysis of surface sediment samples in Project"908"as well as the data of current, topography and tide from other projects. The relationship between sediment movement, tidal current, erosion and deposition is analyzed according to the simulation results. Furthermore, the development and evolution of Liaodong Shoal is explored in this paper. The results reveal that:(1) Tidal current possesses the nature of a progressive wave in the Liaodong Shoal, whose speed reaches peak at high and low tide time. The current speed at high tide time is greater than that at low tide time. During flood tide and ebb tide, tidal current is in transition period with minimum speed. At high tide time, tidal current flows into Bohai Sea through Laotieshan Channel from east to west and moves in radicalized pattern when arriving in the Liaodong Shoal and Bozhong Shoal. It flows to north in the eastern shoal and to Northwest in the western shoal and Bozhong Shoal. At low tide time, tidal current flows out of Bohai Sea.(2) The flow velocity in the crest of sand ridge is larger than that in the trough between sand ridges. The max bottom velocity in the crest of sand ridge and trough is 0.53-0.68m/s and 0.47-0.58m/s respectively at low tide time and then reaches 0.6-0.80m/s and 0.54-0.65m/s separately at high tide time. The angle between current direction and sand ridge axis is about 5-18°.(3) Laotieshan Channel is slightly eroded with the erosion rate of less than 0.1cm/a. The crest of sand ridge is mainly in the condition of erosion, whose erosion rate is no more than 0.2cm/a. Seabed is eroded in some part of trough and in the state of deposition in other part. Bozhong Shoal is dominated by micro-erosion with the erosion rate of 0.0~0.3cm/a. The northeastern seabed of sand ridge is under erosion, whose erosion rate is between 0.1cm/a and 0.3cm/a. The northern and northwestern seabed of sand ridge is in the state of deposition with the deposition rate of 0.3~0.5cm/a. The deposition rate ranges from 0.1cm/a to 0.4cm/a in the south of Bozhong Shoal. The seabed of Jinzhou Bay and Pulandian Bay is under deposition with the deposition rate of 0.0~0.4cm/a.(4) Erosion and deposition within a tidal cycle can be divided into two High Current Erosion phases (HCE), four Middle Current Balance phases (MCB) and two Low Current Deposition phases (LCD). The sand ridge and trough are in High Flow Erosion phase at high tide and low tide time and then step into Low Current Deposition phase when the current direction changes. Sand ridge and trough are in dynamic changes between erosion and deposition in a tidal cycle. The sediment is transported to the north at high tide time and to the south at low tide time. The seabed in the crest of sand ridge and part of trough is slightly eroded as the amount of sediments taken away at High Current Erosion phase is larger than that brought into at Low Current Deposition phase, while the other part of trough is in the condition of deposition.(5) The maximum shear stress of bottom current and the incipient shear stress of sediment movement correspond to each other. The seabed is in the state of erosion, slight deposition and sustaining deposition when the maximum shear stress of bottom current is greater than, close to and smaller than the incipient shear stress of sediment movement respectively.
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