Erosion and abandonment of the Nandu River Delta, Hainan Island

While the area of the Nandu River Delta in Hainan Island of China is only 120 km², the abandoned part accounts for 80 km².According to carbon-14 dating data, stratigraphic facies, and old barrier island analysis results, it is shown that the Nandu River Delta developed from the south to the north toward the Qiongzhou Strait during the period of 4 000~8 000 a BP, and that it developed from the east to the west toward the Haikou Bay during the period of 2 000~4 000 a BP.The deposit center of the delta was diverted toward the Haikou Bay, and the eastern part of the delta was abandoned due to the operation of the prevailing northeast wave.The geomorphic characteristics of the abandoned delta: linear transgressive shore, marsh mud on the beach face, a set of abandoned, semi-abandoned and active river mouths displayed from the east to the west, etc.,are present.Erosion is very obvious in the active delta front.The erosive rate of the shoreline is about 8~10 m/a.The linear scarp along 10 m depth curve was cut by the strait tidal current and the sediment was transported to the east.The northeastern part of the subaquatic delta of the Nandu River mouth was cut by the northeast wave and the sediment was transported to the west and shoreward.