History of Late Holocene Shoreline Changes in the Northern Plain from Bach Dang Estuary to Day River Mouth, Velocity and Causes of Coastal Accretion-Erosion

The period from 1 ka BP to the present, the changes of the Northern plain coastline are extremely complex under the impact of nature and human activities; it can be divided into 3 periods: (1) Period from 1 ka BP to 1787: formation of highstand deltaic sandy mud facies complex (MsamHST Q₂^3). The Nam Dinh area is still accreted more strongly than Thai Binh and Ninh Binh. On the contrary, the Bach Dang estuary area was strongly estuaryizated; (2) The period from 1787 to 1960: due to the great flood that broke the Red River dike in 1787, the Red River was filled up and narrowed, to change its flow to the tributary on the Thai Binh side, flowing into the Ba Lat river mouth and the Red River in Nam Dinh turned into the smaller So River; (3) The period from 1960 to present: the Hai Hau coastline began to erode strongly at an average rate of 25 m/year. Meanwhile, the rate of sedimentary accretion at the Day River mouth increased dramatically by 100 m/year.