Coastal erosion as a major sediment supplier to continental shelves: example from the abandoned Old Huanghe (Yellow River) delta

The Old Huanghe (Yellow River) delta in Jiangsu Province, China, has suffered intense erosion since the river mouth changed from the Yellow Sea to the Bohai Sea in 1855, and this erosion has since been the dominant sediment source to the Yellow Sea and East China Sea. To analyze the topographic and bathymetric changes to the Old Huanghe delta area and derive a regional sediment budget, we extracted shoreline positions and bathymetry from charts and maps published since 1875 and georectified these data into a common coordinate system, combining them with extensive single-beam bathymetric survey data acquired between 2002 and 2008 off Jiangsu Province. The results show continuous seabed erosion throughout the 20th century, consisting of the retreat of shoreface morphology in the nearshore zone (mostly <15-m depth) and deepening of the flat seabed offshore (15 to ~20 m). Off the abandoned river mouth of the Old Huanghe, historically persistent sandbanks disappeared and other recent sandbanks shrank. Sediment yielded by coastal erosion from depths of <20 m has amounted to >790 Mt annually on average for the last 100 years. Of this very large amount of sediment, ~25% is deposited on the offshore slope in the western Yellow Sea, another 20–25% is deposited along the south Jiangsu coast as far as the Changjiang (Yangtze) river delta, and the rest is transported southeastward along the mud belt that crosses the central Yellow Sea to south of Cheju Island in the East China Sea. This amount is an order of magnitude larger than the sediment supply from the modern Huanghe River to the Yellow Sea and also greatly exceeds the present sediment discharge of the Changjiang River.