Morphodynamic responses of Caofeidian channel-shoal system to sequential large-scale land reclamation

Abstract

Understanding the influence of reclamation projects on a channel-shoal system is of vital importance regarding the management and sustainable development of coastal regions. This study addresses the issue by applying a processes-based morphological model to investigate hydro-morphodynamics of Caofeidian channel-shoal in five phases of large-scale reclamation project from year 2003 to 2020. Forced by the spring-neap tidal cycles and representative waves, the model considers multi-fraction sediment dynamics regarding strong spatial variations of mud-sand mixtures in the study area. The numerical results demonstrate that sequential large-scale land reclamation induces continuous loss of sediment volume of tidal flat by reducing its sediment storage capability. The morphodynamics of channels is complex in space and perturbation of reclamation location increases this complexity. For the channels in the western uninterrupted coast, reclamation affects their morphological evolution by damping the long-shore sediment transport. The tidal asymmetry is a key factor in the geomorphology of channels in the eastern inlet-interrupted coast (Laolonggou lagoon-inlet system), which is impacted by the reclamation location. Particularly, reclamation constricting the inlet dampens the flood tidal asymmetry and triggers the deepening of inlet, while tidal flats reclamation in lagoon enhances flood tidal asymmetry which induces the siltation of inlet. The model also reveals different behaviors of multi-fraction sediments, of which the silt with larger settling velocity is subject to the hydrodynamic change induced by reclamation. Although this study is site-specific, the finding provides valuable information for sustainable management of channel-shoal systems in muddy-silt coast under intermittent or sequential land reclamation.