Quantitative Analysis of Rapid Siltation and Erosion Caused Coastline Evolution in the Coastal Mudflat Areas of Jiangsu

Abstract

Muddy coast due to natural and human-induced factors can be variable over a wide range of different spatiotemporal scales. Our limited capability to understand and especially predict this variability can lead to misinterpretation of muddy coastal change information, which hampers informed decision-making and subsequent design and implementation of engineering interventions. Therefore, the research on the evolution of the historical coastline is particularly important. In this study, annual mean coastlines and causes for the variability and possible evolutions are analyzed in a manner that avoids these effects by averaging the instantaneous coastline positions registered during the same year. A set of coastlines is obtained from Landsat MSS/TM/OLI series of remote sensing images taken between 1985 and 2020 in the Google Earth Engine at Jiangsu muddy coast of China Yellow Sea. The coastline is extracted based on the water body index and the Otsu method, and is classified by fractal dimension, annual rate of change, area calculation, center of gravity shift, and artificial index to calculate the temporal and spatial changes in the coastline. The results showed that most of the coastline advanced seaward due to rapid siltation and coastal development in the past 35 years with only a small portion receding landward. The entire coast experienced segmental changes and different evolutionary characteristics and the coastline shifted from rapid erosion to siltation. The silted banks were mainly distributed in the middle section of the coastline in the radial sandbank. The annual change rate in the coast section was 82.21 m/a and the average annual area increased by 18.07 km2. The artificial coastline increased substantially, while the natural coastline gradually decreased due to rapid erosion. From 1985 to 2020, the proportion of artificial coastline in Jiangsu rose from 14% to 77%. The coastline became more curved and the center of gravity of the coastline moved 5.13 km to the northwest by 61°. Before 2000, the driving force affecting the coastline variability was mainly rapid siltation, while the impact of rapid erosion and human activities gradually increased after 2000 with the natural coastline being continuously cut and straightened. Overall, Jiangsu’s muddy coast was the site with the highest anthropogenic pressure and highest vulnerability. However, it is difficult to generalize the results under other conditions, especially on decadal time scales. Scientific and engineering improvements still require more quantitative insight into the physical mechanisms behind the natural and forced shore behavior responsible for the variability to better explain the change process of the coastline and provide a basis for coastal management and sustainable development.