[M-AG32] Satellite Land Physical Processes Monitoring at Medium/High/Very High Resolution

[MAG32-P08] Monitoring Coastal Erosion and Siltation of Port Development Area Using Multi-temporal Satellite Images

*Jui-Han Yang¹, Chi-Farn Chen¹ (1.Center for Space and Remote Sensing Research, National Central University)

Keywords:Remote sensing, Coastal Erosion, Coastal Siltation, Shoreline, DSAS

The coastal environment is subject to diverse influences, including climate change, oceanic tides, and human activities. Taiwan, being an island with a coastline of approximately 1,200 km, is facing challenges related to coastal changes. With the development of the marine economy, coastal infrastructure projects, such as breakwaters and ports, impact coastal erosion and siltation. Hence, monitoring coastal changes becomes a crucial mission. Satellite image technology provides an effective method for large-scale monitoring of dynamic coastal environments.This study utilizes a multi-temporal SPOT satellite image to monitor coastal erosion and siltation in two ports, Taipei Port in northern Taiwan and Hualien Port in the east. Initially, the SPOT satellite images with a spatial resolution of 1.5 meters were collected from 2019 to 2023 to obtain information on coastal changes. Subsequently, the shoreline was digitized for each year using the relatively high water line, provides a dynamically accurate coastal boundary. The maximum distances such as ports (e.g., piers, breakwaters) extending from land towards the ocean were also digitized. These digitized datasets were then used as input for the computation of coastal changes in the Digital Shoreline Analysis System (DSAS). Thirdly, the DSAS system computed the distance and rate associated with shoreline advancement and retreat toward the sea. Net Shoreline Movement (NSM) quantifies the distance the shoreline has moved between two time points, providing an assessment of the overall direction of shoreline movement. End Point Rate (EPR) assesses the average annual rate of coastline movement between two time points, providing an evaluation of the overall average movement speed of the coastline. Positive values for NSM and EPR indicate siltation, while negative values express erosion. Finally, those indices were utilized to compare trends of coastal change in the two study areas.The results reveal a correlation between the maximum length of port structures extending from land to the ocean and the occurrences of coastal erosion and siltation. When a port facility has a longer length (3.08 km for Taipei Port and 1.13 km for Hualien Port), it can obstruct the seawater flow direction, leading to a probability of erosion or siltation. Furthermore, the breakwater construction zone in Hualien Port has a higher degree of siltation, with an EPR of 11.45 m/year, indicating the effectiveness of breakwater in preventing coastal erosion. However, it is noteworthy that the degree of siltation around Taipei Port is also relatively high, with a maximum EPR of 10.8 m/year. Therefore, while breakwaters are effective in protecting the port, special attention must be given to siltation around port areas. From 2019 to 2023, Taipei Port had an average NSM of 32.7 m and an average EPR of 8.14 m/year, while Hualien Port had an average NSM of 6.4 m and an average EPR of 1.68 m/year. According to the data from both study areas, siltation is more severe than erosion (average NSM and average EPR values are positive), which is caused by the harbor breakwater. Additionally, it is worth noting that Taipei Port's siltation is significantly more severe than Hualien Port's due to the topography's impact. Remote sensing provides the government with reference information for future coastal planning and contributes to a more comprehensive and scientific understanding of changes in the coastal environment.