Headland bypassing timescales: Processes and driving forces.

Area of Science:

• Coastal geomorphology
• Oceanography
• Climate science

Background:

• Headland bypassing is a crucial process influencing sediment transport along coastlines.
• Variability in bypassing dynamics affects coastal morphology and stability.
• Understanding long-term and short-term changes is essential for coastal management.

Purpose of the Study:

• To investigate the short-term and long-term variability of natural headland bypassing at Fingal Head, NSW, Australia.
• To determine the relationship between headland bypassing, wave conditions, climate drivers, and anthropogenic interventions.
• To analyze the influence of large-scale climate oscillations on bypassing processes.

Main Methods:

• Utilized nine detailed topo-bathymetric surveys conducted between June 2018 and January 2020.
• Analyzed over 30 years of satellite and aerial imagery to assess shoreline and sandbar position changes.
• Correlated shoreline and sandbar dynamics with wave data and climate indices (ENSO, PDO, IPO).

Main Results:

• Identified two distinct headland bypassing processes, controlled by wave energy and sediment availability.
• Documented bypassing cycles ranging from a few months (sediment leakage) to over seven months (sandbar-driven).
• Observed significant correlations between updrift and downdrift shoreline positions, confirming bypassing influence on longshore transport.
• Found that climate drivers like El Niño-Southern Oscillation influence low-frequency bypassing variability by altering wave direction and sand supply.

Conclusions:

• Headland bypassing at Fingal Head exhibits multi-timescale variability influenced by seasonal, interannual, and decadal climate patterns.
• The intermittent nature of bypassing, driven by specific wave events and sediment conditions, is critical for coastal hazard prediction.
• Effective coastal management requires understanding the periodicity and driving forces of headland bypassing processes.