Abstract
A XBeach surfbeat model is used to explore the dynamics of natural headland rip circulation under a broad range of incident wave conditions and tide level. The model was calibrated and extensively validated against measurements collected in the vicinity of a 500-m rocky headland. Modelled bulk hydrodynamic quantities were in good agreement with measurements for two wave events during which deflection rips were captured. In particular, the model was able to reproduce the tidal modulation and very-low-frequency fluctuations (≈1 h period) of the deflection rip during the 4-m wave event. For that event, the synoptic flow behaviour shows the large spatial coverage of the rip which extended 1600 m offshore at low tide, when the surf zone limit extends beyond the headland tip. These results emphasize a deflection mechanism different from conceptualised deflection mechanisms based on the boundary length to surf zone width ratio. Further simulations indicate that the adjacent embayment is responsible for the seaward extent of the rip under energetic wave conditions. The present study shows that the circulation patterns along natural rugged coastlines are strongly controlled by the natural variability of the coastal morphology, including headland shape and adjacent embayments, which has implications on headland bypassing expressions.
Highlights
Modelled bulk hydrodynamic quantities were in good agreement with measurements for two wave events during which deflection rips were captured
An XBeach surfbeat model was implemented to explore the dynamics of natural headland rips under a broad range of incident wave conditions and tide level
The model was calibrated and extensively validated against data collected in the vicinity of a 500-m rocky headland during two deflection wave events
Summary
Modelled bulk hydrodynamic quantities were in good agreement with measurements for two wave events during which deflection rips were captured. The synoptic flow behaviour shows the large spatial coverage of the rip which extended 1600 m offshore at low tide, when the surf zone limit extends beyond the headland tip. These results emphasize a deflection mechanism different from conceptualised deflection mechanisms based on the boundary length to surf zone width ratio. One of the main driving mechanisms for rip currents is alongshore variations in breaking wave heights [2] These variations can be induced by different causes [3], which include alongshore variations of surf zone morphology (channel rips; e.g., [4]) or a shadowing effect due to the presence of a rigid boundary (shadow rips; e.g., [5]). There is still a scarcity of studies along embayed beaches where boundary-controlled rips can potentially extend much further seaward than other types of rips [10]
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