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南海北部水深８０～２５０ｍ的外陆架和上陆坡海底，有大片沙波地貌分布，它们主要是晚更新世末次冰期低海面时遗留下来的滨海沙波、沿岸沙丘、沙堤和沙垄，属残留沙体地貌，它们的分布规律明显沿着末次冰期时形成的最低海岸线两侧分布，但在现代海底底流作用下，其两翼及沙波谷部发育有次一级的小型沙波或沙纹，它们的形态细小、排列紧密，与残留沙体地貌组成复式海底沙波。人们称这些沙体地貌为流动沙波，它们是不稳定的地质因素，对海底工程有一定危害。但根据外陆架实侧底流数据，运用计算机数学模型方法计算，表明在细砂和中细砂大面积覆盖区，其海底沙波每年均以０．１６８～０．５３４ｍ的速度向深海方向迁移，其移动速度相当缓慢，对海底工程实施不会造成直接危害。
In the northern part of the South China Sea, the outer continental shelf with the depth of 80 ~ 250m and the seabed on the up-slope have large sand wave topography. They are mainly the coastal sand wave left over from the late Pleistocene glaciation and the coastal sand dunes, sand banks and sand dunes, The geomorphology and their distribution are obviously distributed along the lowest coastline formed in the last glacial period. However, under the current ocean floor inflow, there are sub-level small sand waves or sand grains in both wings and the sand valley. Small form, arranged in close, with the residual sand topography composed of composite undersea sand wave. It is said that these sand bodies are in the form of mobile sand waves, which are unstable geological factors and have a certain harm to the seabed works. However, based on the data of the lateral flow in the continental shelf, the calculation by computer mathematical model shows that in the large area of fine sand and medium fine sand, the submarine sand waves migrate to the deep sea every year at the speed of 0.168-0.534 m, Its speed of movement is rather slow and does not pose a direct threat to the implementation of the subsea project.