Remote sensing techniques for exploring waterline influence on shoreline stability in Northwest Ireland

Abstract

Coastal erosion is a global environmental challenge affecting biodiversity, infrastructure, and livelihoods. Remote sensing techniques have improved coastal monitoring, yet many studies focus solely on a single shoreline proxy and neglect the influence of extreme waterlines. This study introduces an integrated methodology that concurrently analyses high waterline (HWL) and low waterline (LWL) positions alongside shoreline (SL) trends, providing a more comprehensive view of coastal dynamics. Applied to three morphologically distinct beaches in northwest Ireland (ranging from dissipative to reflective profiles) over 25 years, this approach reveals how extreme tidal excursions modulate long-term shoreline stability. By simultaneously plotting HWL, LWL, and SL positions, the method identifies hotspot areas where large tidal ranges coincide with notable shoreline movements, highlighting sections prone to erosion or rapid sediment turnover. The results show that the two sites with broader, dissipative morphologies exhibit relatively stable or accreting shorelines under consistent extreme waterline trends, whereas the narrower, more reflective beach displays pronounced variability with the greatest landward shoreline retreats. Seasonal analysis further indicates that winter extreme waterlines lie significantly closer to the backshore baseline than in summer, signalling heightened erosion risk during storm seasons. This novel HWL/LWL-integrated approach yields a more accurate representation of coastal processes across different beach types and provides valuable information for coastal management, improving the prediction of erosion hotspots and informing adaptive strategies.