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Lingding Bay has two main huh ports and connected deep water waterways in South China. Maintaining the stable pattern of "three heaches and two troughs" is the key hasis for the Western trough deepwater waterways development in Cuangzhou Port. Since 2008, due to artificial sand digging on the middle beach, three huge sand pits with total volume of 7 × 108 m3 has been formed, which directly affects the evolution of the beach and trough in Lingding Bay. By means of field investigation and numerical simulation, the influence of sand mining on surrounding water body and topography is analyzed. It is pointed out that the sediment concentration in the sediment digging area can increase greatly from 0.2 kg/m3 to 1.5-2.8 kg/m3 (up to 5 kg/m3). This will increase the deposition of the nearby seabed and also affect the waters of the Hong Kong-Zhuhai-Maeao Bridge. The influence of hydrological factors on the formation of sand pits are calculated. The results show that the main changes of tide level, tidal current and tidal volume are in the sand pit and its adjacent waters. The main changes are the tidal level decreases (less than 1cm), the tidal current decreases, and sediment deposition is mainly in the sand pit (33 cm/a). The seabed around the pit is scoured, and the scour in the south side is larger. At present, sand pits are mainly silted up, and the time of silting back is expected to take 20 years. When 2#, 3# sand pits or 2#, 4# sand pits are connected, it is possible to form a new tidal current channel, change the existing pattern of "three beaches and two troughs", and have a negative impact on the existing channel maintenance and port production. [ABSTRACT FROM AUTHOR]

Human activities, involving construction such as large-scale bridge projects in tidal estuaries, can lead to undesirable and severe morphodynamic responses, such as excessive siltation in the harbors and channels. Lingdingyang Bay of the Pearl River Estuary (LBPRE) is a typical bay with unique geomorphological features that might cause complex changes in hydrodynamic features and sediment movement. The LBPRE includes a number of harbors and channels, including Nansha Harbor of Guangzhou Port and the western harbors of Shenzhen Port, which are two hub ports in South China, and their corresponding and important Lingding and Tonggu channels. Designed to cross over the LBPRE to connect Hong Kong, Zhuhai, and Macao, the proposal of the Hong Kong–Zhuhai–Macao Bridge (HZMB) is a representative of the most complicated and the longest sea-crossing transportation project in the world, which consists of several segments of bridge, a tunnel, and two man-made islands. Therefore, it is of extreme significance to demonstrate the effects of the HZMB on the relevant harbors and channels through study. In this article, a large-scale physical model of tidal currents and sediment movement, covering the entire LBPRE with a horizontal scale of 1:900 and a vertical scale of 1:120, was presented with emphasis on the effects of the HZMB on water flow and sediment movement. The design and layout of the model are described in detail. The accuracy of the model was verified with in situ data; the results show that the simulated tidal levels, currents, and deposition in the channels are all in good agreement with measured field data. Then, evaluation on the effects of the HZMB was carried out by comparing the scenarios with and without the bridge; the effects on hydrodynamics of the LBPRE and the erosion and deposition occurring in the harbors and channels were analyzed. The following main conclusions were reached. (1) The effects of the HZMB on tidal levels, currents, and prisms were all relatively small, and the influence was limited within an area of 5 km upstream and downstream from the bridge. The construction of the HZMB tends to lead to increase of the tidal currents in Lingding Channel between the two man-made islands, which is favorable for maintenance of water depth in the channel. (2) The effects of the HZMB on erosion and deposition in the harbors and channels are insignificant. (3) The construction of the HZMB is not predicted to have substantial effects on changing the pattern of the shoals and channels in the LBPRE. (4) The HZMB is feasible as far as its effects on hydrodynamics, harbors, and channels are concerned. • A physical model of tidal currents and sediment covering the entire Lingding Bay of the Pearl River Estuary was successfully designed, built and verified with in situ data. • The physical model was successfully applied to perform experimental simulations before and after the construction of the Hong Kong–Zhuhai–Macao Bridge. • The experimental predictions based on this physical model have been proven to be reasonable and correct. [ABSTRACT FROM AUTHOR]