Sustainable management of muddy tidal flats

Abstract

Tidal flats play a critical role in coastal systems. They serve as essential buffers that protect inland communities from flooding by storm surges, contribute significantly to the maintenance of coastal biodiversity, and function as crucial sites for carbon sequestration. Moreover, they are indispensable for land reclamation projects, supporting economic activities such as agriculture and aquaculture. However, rapid coastal economic development and assertive human interventions have intensified conflicts of interest between socio-economic demands and the preservation of these fragile ecosystems. This increasing tension underscores the necessity for a detailed understanding of tidal flat evolution and the complex interplay between natural processes and anthropogenic activities.

This research aims to deepen our understanding of unvegetated tidal flat morphodynamics by examining both natural processes and the impacts of human interventions. The insights gained will provide valuable theoretical guidance for the sustainable and effective management of tidal flat resources in the future. To achieve this, the study focuses on tidal flats along the Jiangsu Coast in China as a case study. Because it is a typical example famous for its extensive and diverse tidal flat systems. At the same time, it has a long history of coastal land reclamations. A multi-faceted approach is adopted, combining field dataset analysis, a process-based Delft3D model, and a hybrid DET-ESTMORF model, which together provide a robust foundation for theoretical insights in sustainable coastal management.

Based on a unique field measurement data along the Jiangsu Coast, the morphology and sediment characteristics of the unvegetated intertidal flats along this coast are analysed. Both cross-shore and alongshore variations are observed. In the cross-shore direction, sediments exhibit a pronounced coarsening from the landward to the seaward side, indicating tide-dominated forcing. In the alongshore direction, the coast is divided into two parts depending on its morphological state. The northern coast, which is predominantly eroding, exhibits steeper intertidal slopes and a complex mix of sediment types, ranging from extremely fine to coarse deposits. The variation in sediment composition is attributed to natural processes such as self-weight consolidation and surface armouring. In the accreting southern coast, while tidal flat slopes are generally becoming milder towards the south, the corresponding bed surface sediment grain size is becoming coarser southward. This relationship between slope and sediment grain size in the southern coast is opposite to the findings on other muddy tidal flats.

In order to investigate the mechanism behind the region-specific alongshore pattern of the southern Jiangsu Coast, we formulate a conceptual model with special focus on describing the alongshore variations in hydrodynamics and shoreline evolution. Subsequently, a highly schematized Delft3D numerical model is employed in diagnostic mode. By integrating these approaches, the sediment provenance is found to be the sole factor capable of explaining the observed pattern.

Apart from natural processes, anthropogenic activities can also induce significant changes in tidal flat morphology. Available information on the tidal flat morphological responses to human interventions is limited based on the single-time measurements data. We therefore evaluate the resilience of tidal flats to anthropogenic disturbances (specifically, upper flat enclosure reclamation) using an extended DET-ESTMORF model. A series of sensitivity tests under various environmental conditions is conducted with this model. Our findings indicate that the concave or convex shape of tidal flat profiles is primarily governed by dominant hydrodynamic forces (whether tidal or wave-driven), while other variables modulate the profile slope. For a tidal flat to revert to its pre-reclamation configuration, it must exhibit continuous seaward progradation under natural conditions. Such restoration typically occurs in environments with abundant sediment supply, subdued wave activity, and the absence of cross-shore constraints imposed by shore-parallel tidal channels.

Overall, the insights derived from this study enhance our understanding of the interactions between natural hydrodynamic processes, sediment dynamics, morphology change and human-induced alterations. The findings highlight the importance of continuous monitoring and the adoption of adaptive management strategies to ensure that coastal development preserves the ecological integrity and long-term stability of tidal flat systems.