Abstract
Cross-shore profiles and environmental forcing were used to analyse morphological change of a headland bay beach: Tenby, West Wales (51.66 N; −4.71 W) over a mesoscale timeframe (1996–2013). Beach profile variations were attuned with longer term shoreline change identified by previous research showing southern erosion and northern accretion within the subaerial zone and were statistically significant in both sectors although centrally there was little or no significance. Conversely a statistically significant volume loss was shown at all profile locations within the intertidal zone. There were negative phase relationships between volume changes at the beach extremities, indicative of beach rotation and results were statistically significant (p < 0.01) within both subaerial (R2 = 0.59) and intertidal (R2 = 0.70) zones. This was confirmed qualitatively by time-series analysis and further cross correlation analysis showed trend reversal time-lagged associations between sediment exchanges at either end of the beach. Wave height and storm events displayed summer/winter trends which explained longer term one directional rotation at this location. In line with previous regional research, environmental forcing suggests that imposed changes are influenced by variations in southwesterly wind regimes. Winter storms are generated by Atlantic southwesterly winds and cause a south toward north sediment exchange, while southeasterly conditions that cause a trend reversal are generally limited to the summer period when waves are less energetic. Natural and man-made embayed beaches are a common coastal feature and many experience shoreline changes, jeopardising protective and recreational beach functions. In order to facilitate effective and sustainable coastal zone management strategies, an understanding of the morphological variability of these systems is needed. Therefore, this macrotidal research dealing with rotational processes across the entire intertidal has significance for other macrotidal coastlines, especially with predicted climate change and sea level rise scenarios, to inform local, regional and national shoreline risk management strategies.
Highlights
Beaches situated in the lee of rocky outcrops or headlands, generally take some form of curvature known as curved, embayed, hooked, pocket and headland-bay beaches [1] and 51% of the world’s coastlines are representative of this morphology [2]
The profiles were truncated to the high spring tidal level; sectional volumes, i.e., the morphological variables, were determined directly from the Regional Morphology Analysis Package (RMAP), where volume is calculated by extrapolating the area under the curve for one unit length (m3·m−1) of shoreline [40] (Figure 2b)
The study has examined available information on storm characterization, wave models and beach level and volume change over a 17-year period to establish if beach rotation and morphology changes, identified by Thomas et al [16], continued at South Beach, Tenby, West Wales
Summary
Beaches situated in the lee of rocky outcrops or headlands, generally take some form of curvature known as curved, embayed, hooked, pocket and headland-bay beaches [1] and 51% of the world’s coastlines are representative of this morphology [2]. Along these coasts, nearshore wave energy is often high as waves are related to bathymetry and refraction/diffraction patterns [3]. Understanding beach morphological variability is essential to support coastal risk assessment and help in the decision making process, especially in what concerns the implementation of mitigation measures in response to erosive events reported worldwide [8]. Shoreline rotation phenomenon can be defined as a landward or seaward movement at one end of a beach accompanied by the reverse pattern at the other end [7] and is known to be caused by variations in wave climate such as wave approach direction and energy flux [7,9,10,11,12,13]
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