Sea-level changes modulate beach face slope in coastal upwelling zones

Area of Science:

• Coastal geomorphology
• Oceanography
• Sediment dynamics

Background:

• Beach profile evolution is traditionally attributed to wave action.
• Observed beach slopes do not always correlate directly with incident wave conditions.
• Mechanisms governing transitions between beach equilibrium states are poorly understood.

Purpose of the Study:

• To analyze beach profile data and characterize nearshore transient periods.
• To investigate the influence of non-wave-driven processes on beach morphology.
• To identify factors causing deviations from predicted equilibrium states.

Main Methods:

• Analysis of 3.5 years of daily beach profile data from two tropical low-tide terrace sites.
• Characterization of nearshore transient periods between seasonal equilibria.
• Complementary laboratory experiments validating observed dynamics.

Main Results:

• Identified episodes where traditional equilibrium beach classifications failed to predict slope evolution.
• Demonstrated that water-level variations, linked to coastal upwelling, influence sediment redistribution.
• Confirmed that both wave energy (Dean number) and water-level variability drive observed beach dynamics.

Conclusions:

• Transient sea-level modulations (e.g., upwelling, eddies, atmospheric systems) reshape beach profiles across multiple timescales.
• Existing equilibrium frameworks need to be extended to incorporate non-wave-driven processes.
• Understanding these transient dynamics is crucial for accurate coastal management and prediction.