Influence on the sandy coast evolution of the ocean engineering——A case study of artificial Riyue island, Wanning city, Hainan Island

The construction projects on artificial Riyue islands have led to a fast change of coastal erosion and deposition on Riyue bay.The erosion of the southwest coast has threatened the development of the vitica mangachapoi forest natural reserves on the land.Monitoring and management of Riyue bay becomes an urgent demand.With the studies of multi-temporal remote sensing images and four groups of costal testing data, following erosive and depositional effects of constructions on Riyue bay can be discussed.Due to the depositional growth of shadow zone of artifical Riyue islands, a tombolo was formed in 2016 with a width of 370 meters and a length of 1, 500 meter; at the northeast side of artifical Ri island, erosion was created because of the wave refraction and diffraction after the construction was done, witch with a width of 20 meters and a length of 380 meters.At the southeast side of artifical Ri island, severe erosions and retreats were found.The erosive width is around 40 meters and the erosive length is around 2, 000 meters.The construction projects on artifical Yue island have improved the erosive problems on southeast side.However, 800 meters of costal line still lays in an erosive state.Considering the natural situations and technical capacities comprehensively, the combination of groyne, artificial sand filling as well as ecological conservation of ipomoea pes-caprae would be the most suitable solution.