Abstract
The study investigates cross-shore outer sand bar dynamics in an open-coast non-tidal beach at the Bulgarian Black Sea due to wave climate. On seasonal to short-term (1–2 years) time scale, monthly field measurements of the outer bar profiles were related to respective modeled nearshore wave data. Hereby, seaward-shoreward bar migration was examined depending on the wave forcing, wave non-linearity, wave transformation scenarios, storms and direction of wave incidence. Analysis revealed that intra-annually highly non-linear waves were responsible for outer bar displacement, while the direction of migration depended on wave period, duration of conditions with wave steepness >0.04, angle of approach and total duration of storms. Short-term bar evolution was mainly governed by wave height and storms’ parameters as the angle of approach and duration. The correlation between the outer bar location and wave height annual variations initiated the first for the explored Black Sea region examination of possible connection between wave height’s temporal fluctuations and the variability of climatic indices the North Atlantic Oscillation (NAO), the Atlantic Multi-decadal Oscillation (AMO), the East Atlantic Oscillation (EA), the Arctic Oscillation (AO), the East Atlantic-Western Russia (EA/WR) and the Scandinavian (SCAND) patterns. According to the results the inter-annual outer bar location may vary depending on periods of maximum annual wave fluctuations, which in turn predominantly depend on indices the EA (4–5, 10–11, 20–30 years), the EA/WR (2–4, 9–13 years) and the NAO (15 years).
Highlights
The nearshore environments of mild-sloped sandy beaches are often characterized by the presence of a variety of morphological features, as most common are sand bars
Sand bars are often found at depths less than 10 m and within or just seaward of the surf zone, whose width is influenced by variations in the incident wave climate
The presence of sand bars in the coastal zone is of significant importance for sandy beach morphodynamics since they act as a storage of sediments and as a natural protection by dissipating high wave energy during storms by breaking, limiting coastal erosion and flooding hazards [10,11]
Summary
The nearshore environments of mild-sloped sandy beaches are often characterized by the presence of a variety of morphological features, as most common are sand bars. The presence of sand bars in the coastal zone is of significant importance for sandy beach morphodynamics since they act as a storage of sediments and as a natural protection by dissipating high wave energy during storms by breaking, limiting coastal erosion and flooding hazards [10,11] These morphological features may exert a significant impact on the nearshore hydrodynamics due to their cross-shore and long-shore geometry and location [12,13]. The first study that has associated the sand bar migration with changes in the climatic indices (the North Atlantic Oscillation in particular) is [41] They confirmed the existence of such connection based on 15-year time series of Argus video images on the evolution of the submerged profile in the Perranporth beach. Their content decreases, and at 8–10 m depth over 90% of the sediments consist of particles less than 0.25 mm in size [45,47]
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