Influence of giant artificial sand pits on the natural evolution of Lingding Bay

Lingding Bay has two main hub ports and connected deepwater waterways in South China. Maintaining the stable pattern of "three beaches and two troughs" is the key basis for the Western trough deepwater waterways development in Guangzhou 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 5kg/m³). This will increase the deposition of the nearby seabed and also affect the waters of the Hong Kong-Zhuhai-Macao 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 1 cm),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.