Wave dynamics and potential longshore sediment transport at Shippagan, Gulf of St Lawrence: insight into seasonal variability and extreme weather events

This study examines the wave climate and its influence on potential Longshore Sediment Transport (LST) along the Shippagan coast of the Gulf of St. Lawrence, eastern Canada. Using a combination of in-situ observations and ERA5 reanalysis data, the research evaluates both seasonal and annual variations in wave dynamics and sediment transport, with particular attention to the role of extreme weather events. The wave climate shows pronounced seasonality, with higher wave activity in winter and lower activity in summer, while wave direction remains consistently from the southeast. Estimated potential LST rates, derived from renowned three empirical formulae, i.e., CERC, Kaczmarek and Komar show variability in both magnitude and direction over the three-year study period (2021-2023), reflecting the complex sediment dynamics of the region. According to CERC formula, the estimated net annual rates were -6.0 to 6.4 x10⁵ m 3 , while estimates from the Kaczmarek formula ranged from -6.1 to -1.8 x10⁵ m 3 over the same period. The Komar formula provided net annual LST estimates ranging from -6.2 to 6.5 × 10⁵ m³, which are in close agreement with the CERC results. The predominant direction of net potential LST rates is towards southeast direction. Seasonal analysis highlights winter season waves are the dominant contributor to sediment transport, followed by spring and fall. Although, post-tropical storms contributed 5% to the total gross potential LST rates. Additionally, long-term analysis (1992–2023) reveals increasing trends in wave heights (0.4 cm year -1 ) and potential LST rates. These findings provide valuable insights into sediment dynamics, supporting improved modeling and prediction of the fate of nourished sediments, and contributing to the optimization of nature-based solutions like the Sand Engine for sustainable coastal management.