Monitoring multidecadal coastline change and reconstructing tidal flat topography

Abstract

Intertidal zones are vulnerable to both landward and seaward pressures, i.e., sea level rise and aquaculture expansion. Thus, the conservation of coastal habitats has reached international prominence, as addressed in Sustainable Development Goal (SDG) target 14.5. Nevertheless, stakeholders often have limited resources to monitor ample intertidal zones and cannot effectively evaluate actual conservation progress. Modern satellite imagery, especially optical data, provides a cost-efficient opportunity. Nonetheless, most past studies relied on noise-included water indices and demanded intensive manual editions. Therefore, this study presents an automatic processing strategy to estimate essential baseline information of coastal dynamics and topography, including shoreline changes, intertidal digital elevation model (DEM), and mean sea level (MSL). The results were statistically validated with bathymetric surveys and indicated that our proposed workflow can identify hotspots of coastal erosion-accretion and topographic features. Methodologically, by incorporating a fine-resolution global tide model, the tidal effect was greatly mitigated. We confirm that images acquired during flood stages can yield better quality tidal flat DEMs. The shoreline extraction approach refined in this study also enhances the positional accuracy via overcoming common biases, including water color variations and breaking wave-induced whitewash. These improvements and the wide applicability of our approach highlight the opportunity of utilizing spaceborne remote sensing data to assess the coastal stability in different spatio-temporal scales.

Keywords

• Shoreline mapping
• Coastal management and governance
• Sustainable conservation
• Geomorphology
• Intertidal elevation
• Integrated coastal zone management (ICZM)