Evolution Modeling and Protection Scheme for Tidal Flats Under Natural Change and Human Pressure, Central Jiangsu Coast

Amidst escalating global changes and heightened human activities, tidal flats worldwide are facing a transition from accretion to erosion. In order to quantify the growth pattern of tidal flats and its response to changes in multiple external driving factors, here we established a geometric model, in combination with field surveys, to study the historical behavior (1127-1990) and future trends (2100) of a typical tidal flat system on the Jiangsu coast, China. The results indicate that sediment supply and relative sea level change determine the accretion-erosion status and the eventual morphological pattern of the tidal flat. If these two factors remain stable and sediment supply can compensate for the increase in sediment accommodation space caused by sea level change, the tidal flat will continue to accrete until its growth limit is reached. Otherwise, tidal flats will face erosion risk, which can be further enhanced by localized land subsidence. Furthermore, changes in the coastal profile show a trend of progressive retreating, with the lower part of intertidal zone being eroded more rapidly than its upper part. This demonstrates that the sediment supply has been reduced to such a level that the present "in-transition" evolution pattern of central Jiangsu coast will soon be replaced by severe inundation and erosion. Hence, we advocate for a comprehensive, multi-tiered coastal protection strategy focusing on wave suppression, enhancement of sediment retention, and increased storm resistance. This strategy underscores fundamental underlying mechanisms of the accretion-erosion transition, which is crucial for the future safeguarding of coastal wetlands globally. Tidal flats are important potential land resources. Over the Holocene period, under increased sediment from rivers has led to rapid growth in most coastal areas, supporting the prosperity of coastal cities. However, uncertainties exist regarding the limits of this growth, and global changes and human activities are causing tidal flats worldwide to shift from growth to erosion. To understand the tidal flats growth patterns and their response to future challenges, we developed a geometric model based on key processes. Field surveys and a millennium-scale study in eastern China support the model's reliability. Our findings highlight sediment supply and relative sea-level change as key factors in tidal flat evolution, with growth limitations even with sustained sediment supply. We propose a protective scheme based on tidal flat evolution mechanisms to enhance coastal resilience against global change. Geometric modeling is employed to simulate the evolution of a transitional tidal flat system and tested against historical processes The central coast of Jiangsu, China, is anticipated to reach its growth limit and become eroding around 2065 A stepped green protection scheme, designed in a manner progressing from sea to land, is established to safeguard coastal wetlands