Transformation of the Three Largest Chinese River Deltas in Response to the Reduction of Sediment Discharges.

Tan, C.; Huang, B.; Liu, F.; Yang, Q.; Jiang, C., and Zhang, S., 2016. Transformation of the three largest Chinese river deltas in response to the reduction of sediment discharges. The Yellow, Yangtze, and Pearl rivers deliver more than 1.2 × 10¹² m³/a of freshwater and 13.6 × 10⁸ t/a of sediment into the western Pacific Ocean, playing important roles in the morphological evolution of the ocean in this region. From the 1950s to the 2000s, the total sediment loads of the three rivers decreased by 81.2%; this change has been primarily caused by human activities, such as dam construction and water-soil conservation projects. The sediment loads in the Yellow, Yangtze, and Pearl rivers decreased by 89.9%, 62.1% and 57.1%, respectively, from the 1950s to the 2000s. In response to the sediment supply decrease, the sediment regimes of the river channels in the lower reaches of the three rivers generally transitioned from deposition to erosion since the 1990s. The erosion of the channel has modulated the characteristics of the suspended sediment delivered to the estuary; for example, the erosion of the lower river channel increased the sediment flux and caused relatively coarser suspended sediments to be delivered to the estuary. As a consequence of the changes in the river basins, the evolutions of the three river deltas have transformed in the 2000s. The subaqueous deltas of the Yellow and Yangtze rivers changed from deposition to erosion. However, the Pearl River delta generally prograded seaward, and a portion of its subaqueous delta ( e.g., the Modaomen River mouth) underwent erosion. In the coming decades, the sediment discharges into the seas from these three rivers are likely to decrease further because of intensifying human activities. Therefore, enhanced erosion in the three river deltas will continue when the river deltas remain unprotected. Our study demonstrates that human activities in the three river basins can influence the morphological changes of the estuaries, indicating that a river basin and its coastal zone are an integrated system. [ABSTRACT FROM AUTHOR]