Abstract

The Cồn Nổi (Emergent Sandbar) area is situated in the estuary of the Đáy River, Kim Son District, Ninh Bình Province. This is a typical region of sediment deposition for river-sea interaction. In addition, this area also plays an important role in master planning for marine economic development of the region. The research results show that the surface sediments of the Cồn Nổi area are mainly composed of sand, silty sand, sandy silt containing mica flakes. The interaction between the Đáy River, wave, tide and sediment supply demonstrates that the southeastern side of Cồn Nổi is characterized mainly by coarse sediments and erosional regime while the western and southwestern sides demonstrate deposition of fine-grained sediments. The Cồn Nổi tends to migrate toward the west. Initial results of this study revealed that the deficiency of sediment supply due to the construction of hydropower reservoirs in the upstreams of the Red and the Đà rivers is considered the main cause of coastal erosion along the coast of North Việt Nam in general and in the Cồn Nổi area in particular.