Morphological Evolution and Driving Factors of Tidal Flats in the Yangtze Estuary (China) During 1998–2019

Abstract

AbstractThis paper studies the morphological evolution and driving factors of the tidal flats in the Yangtze Estuary (YE), based on the bathymetric data over the last 20 years (1998–2019) and a three-dimensional numerical model (SWEM3D). The results show that: In the past two decades, the combined action of fluvial sediment decline and estuarine engineering has changed the morphological evolution trend of tidal flats in the YE. The fluvial sediment decline caused the decrease of suspended sediment concentration successively from the inner estuary to the mouth bar area (the outer estuary), which led to the erosion and steepening of the tidal flats in the YE, and the erosion of tidal flats in the inner estuary was earlier and more obvious than that in the mouth bar area. The estuarine engineering is the main controlling factor of the distribution and trend change of erosion-deposition in the adjacent tidal flat. The waterway regulation projects promoted the deposition of tidal flats within its sheltered area, while the reclamation and reservoir projects intensified the erosion of the lower tidal flats nearby. As for the remaining non-human-intervention tidal flats, those adjacent to the mainstream of ebb current in the inner estuary were significantly eroded, while those on the north side of the channel were slowly deposited due to the weaker hydrodynamics. In the future, the fluvial sediment supply may keep decreasing and maintain a lower level under the continued influence of anthropogenic activities in the Yangtze River basin, the unprotected tidal flats in the YE will face a risk of further erosion. It is necessary to take appropriate protection measures to improve the ecological service function of the tidal flats in the YE.