Redai dili (Nov 2024)
Analysis of Coastline Changes in Zhanjiang Bay from 1973 to 2023
Abstract
The coastline of Zhanjiang Bay has undergone profound changes under the combined action of natural and human factors, making the rational protection and utilization of coastal resources a research hotspot. As a typical tropical bay in China, analyzing the coastline changes in Zhanjiang Bay can provide basic data to support the development and utilization of coastal zones. In this study, 42 optical satellite images from 1973 to 2023 were used in conjunction with the random forest method to extract the shoreline, analyze the spatiotemporal evolution of the Zhanjiang Bay coastline, and investigate its driving factors. Additionally, shoreline complexity changes were explored, and Gross Domestic Product (GDP) was introduced for the correlation analysis of shoreline indicators. The results showed that the total length of the Zhanjiang Bay coastline increased by 103.13 km over the past 50 years. Coastline changes are influenced by both natural and anthropogenic factors, with anthropogenic factors having the most significant impact. Natural factors include erosion caused by storm surges, sea level rise, and dynamic coastal conditions. Anthropogenic factors include construction of coastal aquaculture farms, land reclamation, coastal engineering projects, coastal infrastructure development, and industrial land development. The main areas of change were concentrated along the main channel and the Nansan Waterway. The proportions of shoreline segments expanding seaward on the east and west coasts were 51.4% and 71.6%, respectively, whereas the landward erosion shoreline segment on Donghai Island was 58.0%. Specifically, the southeastern section of the east coast experienced massive shoreline expansion. Coastal engineering along the west coast, southeastern village, and town construction projects on the east coast resulted in shoreline advancement of more than 2 km seaward. Erosion was observed at the western end of the coastline, across several estuaries from the west coast, and along the shoreline of the Nansan Channel on the south side of the east coast, with the most severe shoreline erosion occurring at the end of the west coast shoreline, where the average setback was 1 km, with a maximum setback of nearly 1.8 km. Except for the 2010s, the change in the intensity of the coastline of Zhanjiang Bay was positive. The fractal dimension of the coastline increased from 1.086 to 1.124, consistent with the trend in its length. The primary driver of coastline expansion was large-scale land reclamation on the western bank of Zhanjiang Bay, southwestern bank of the eastern bank, and northern part of Donghai Island, with a total reclaimed area of 82.82 km2. The proportion of the reclaimed area after 2010 reached 57.5%, the area of coastal aquaculture farms increased by 26.98 km2 over the past 30 years. Large-scale erosion occurred on the eastern and southern sides of Donghai Island. In addition, the fractal dimension and length of the Zhanjiang Bay coastline were strongly negatively correlated with the inverse of the GDP of Zhanjiang, with correlation coefficients of -0.96 and -0.99, respectively. These findings suggests that the economic benefits of shoreline shifting can be quantified using shoreline indicators, whereas differences in shoreline indices between different harbors affect the relevance of the economic benefits. Owing to the narrow and long topographic structure of Zhanjiang Bay, there is a delay in tidal signal propagation from the bay mouth to the interior. Therefore, when exploring the water margins obtained from optical remote sensing images, the water level information of the corresponding region must be utilized to correct the tidal variations in Zhanjiang Bay. Based on this, numerical models will be used in the future to obtain tidal data for each region and the corresponding water margins.
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