Effects of vegetation expansion on morphodynamics of tidal channel networks

Abstract

Evolution of coastal landforms, including the formation and development of tidal channel networks in salt marshes, is shaped by the interaction of surface water hydrodynamics, sediment transport and vegetation dynamics. However, the impact of vegetation expansion on tidal channel geomorphology remains unclear. In this study, an ecogeomorphic model coupling abiotic and biotic processes was developed to investigate the effects of vegetation expansion (i.e., seeding and cloning) on tidal channel morphodynamics. The numerical model results demonstrate that vegetation expansion promotes the formation and development of tidal channels. With vegetation cover, the number, total length, area and volume of tidal channels markedly increase. Vegetation also reshapes the cross-sections of tidal channels, increasing channel depths and decreasing their width-to-depth ratios. The synergistic effect of seeding and cloning is more significant than either process alone, leading to enhanced flow convergence and bed shear stress. Consequently, the channel erosion is enhanced, laying the foundational framework for the formation and growth of tidal channel networks. A high expansion rate enhances the effect of vegetation on tidal channel morphodynamics, leading to more developed tidal channel networks. This study focuses on tidal channel networks in salt marsh ecosystems and advances understanding of the geomorphological evolution of tidal channel networks subject to vegetation expansion, and it offers further implications for the management of coastal wetland ecosystems.