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Thomas T.,Carmarthenshire County Council | Phillips M.R.,University of Swansea | Williams A.T.,University of Swansea | Jenkins R.E.,University of Swansea
Progress in Physical Geography | Year: 2011

Beach profile surveys, offshore wave climate and variations in atmospheric conditions have been utilized to assess a short-term beach rotation phenomenon in a headland embayment Tenby, West Wales. Beach rotation, expressed by subaerial volumetric change, was shown by a negative phase relationship between beach extremities (r = -0.67), while cross-correlation at a one-month timelag increased statistical significance (r = 0.84). Due to beach aspect, gale wave heights decreased as wave direction rotated to the south (R2 = 0.4) and west (R2 = 0.65), while offshore wave direction influenced change at the southern and northern extremities (R2 = 0.52 and 0.34, respectively). Shelter from offshore islands and Giltar Headland contributes via wave diffraction to accretive, erosive and rotational patterns, and these are sensitive to variations around the predominant wave direction (229°). A southerly shift induces north/south sediment movement, as waves diffract around the offshore islands, while a westerly change results in south/north sediment movement (i.e. beach rotation), as diffracted wave domination transfers to the headland. A general gale wave height reduction occurred when the North Atlantic Oscillation (NAO) was weak or in a transitional phase between positive or negative phases (R2 = 0.69 and R2 = 0.72, respectively). Morphological change was also attuned to atmospheric variation where a reversal in beach rotation was influenced by variations in positive and negative NAO/volume correlations and longshore profile location (R2 = 0.54 and 0.69, respectively). The results of this study have wider implications for coastal management; it is suggested that models developed in similar systems elsewhere will form the basis of human intervention or no active intervention strategies. © The Author(s) 2011. Source


Thomas T.,Carmarthenshire County Council | Phillips M.R.,University of Swansea | Williams A.T.,University of Swansea
Journal of Coastal Research | Year: 2011

This paper investigates how the presence of offshore Islands influence the morphological behaviour in a headland embayment Tenby, West Wales [GR 212200, 198599]. Beach profile surveys and offshore wave climate have been utilised for this assessment. The majority of gales (75%) emanate from the southeast to westerly direction. Here, analyses of gale wave direction showed that the offshore Islands give shelter. These effects decrease with wave rotation, the highest waves emanate from directly behind the Islands, and decrease in height with rotation irrespective of direction. Southeast shifts generate waves within the shorter (fetch limited) Bristol Channel, and during southwest shifts, there is an interaction with the updrift Pembrokeshire coastline. Wave diffraction has a considerable influence on South Beach behavioural patterns, as wave direction rotates. Moreover, southeast shifts give rise to dominate wave diffraction around the easternmost point of Caldey Island, under these offshore wave conditions a trend of rising volume within each beach region was observed. In contrast, westerly shifts gave rise to dominant diffraction around the Giltar headland itself, and a loss of protection given by the offshore Islands. Under these offshore wave conditions, lowering volumes in all beach regions was observed. It is accepted that more detailed studies of wave diffraction and refraction are required to fully understand their consequences on South Beach morphology. However, sheltering effects of natural protection that prevents direct arrival of wave energy, has implications for coastal zone management, and careful examination of these phenomena are required both over short and longer timescales. Source


Thomas T.,Carmarthenshire County Council | Phillips M.R.,University of Swansea | Williams A.T.,University of Swansea | Jenkins R.E.,University of Swansea
Applied Geography | Year: 2012

Beach profiles, gale climate, atmospheric variations and wave models (RCPWave) were used to assess beach rotation at two adjacent macrotidal open coast beaches, Pendine and Cefn Sidan Sands, West Wales. Results identified an 11 year record of rotation on both beaches where negative phase relationships were established between volume change at beach extremities within both subaerial and intertidal zones. In the absence of headlands to trap sediment, it is asserted that the driving force for beach rotation is the presence of two estuary complexes that act as surrogate headlands. Wave models found agreement with statistical analyses and showed that under dominant south-westerly waves, sediment movement is towards the estuary complexes, while subdominant south-easterly waves generate counter drift. This was supported by illustrations of sediment pathways for varying wave directions. NAO Index values change from positive to negative trends through time and were correlated to morphological change in both littoral settings. Beach volume change lagged NAO variation by six months at Pendine Sands and by up to two years at Cefn Sidan Sands, with opposing correlations observed at beach extremities. This suggests that rotation is caused by a reversal in NAO trends. These new findings are likely to be exhibited at other open coast locations and this work should be repeated elsewhere to inform coastal management strategies. © 2012 Elsevier Ltd. Source


Thomas T.,Carmarthenshire County Council | Phillips M.R.,University of Swansea | Williams A.T.,University of Swansea | Jenkins R.E.,University of Swansea
Applied Geography | Year: 2012

Medium term (decadal) beach profile response to external forcing was assessed on two adjacent embayed beaches (North and South Sands) in Pembrokeshire, West Wales. Both have contrasting physical and geological characteristics: a headland bay backed by dunes and a constrained embayment backed by geological promontories, promenades, walls and rock revetments. Paired t-tests showed significant changes at all cross-shore profile locations (95% confidence), with south and north shores respectively exhibiting falling and rising beach levels. South to north sediment transport was revealed by volumetric variation (r = 0.83), and longshore sediment distribution (r = 0.91). North Beach level variations lagged behind South Beach by one-year (r = 0.85). A reduction in high wind speed frequency, coincidental to spring tides, was correlated with falling South Beach levels (r = 0.87) and rising North Beach levels (r = -0.92). Heavily refracted Atlantic swells also have contrasting effects on these systems. Multiple regression models applied to beach level change for both systems showed high correlation (R2 = 0.93 and 0.85 respectively), suggesting that swell wave period and strong north-westerly winds that occur during high spring tides had cumulative effects. Furthermore, variations in the North Atlantic Oscillation (NAO) index were correlated to cumulative changes in mean sea level, wind wave height and south-westerly winds (R2 = 0.75). While NAO variations were linked to variations in South Beach morphology, it was insignificant on North Beach (r = -0.72 and -0.14 respectively). Cross-correlation analyses showed that North Beach morphological changes lagged behind NAO Index variation by one-year with much improved correlation (r = 0.77). A similar scenario existed when comparing Mean Sea level and beach level differences (r = -0.54 and -0.32 respectively). Similar behaviour should be exhibited at other worldwide embayments, and it is suggested that this work is repeated to establish specific responses, to will underpin intervention or no active intervention strategies. © 2011 Elsevier Ltd. Source


Thomas T.,Carmarthenshire County Council | Phillips M.R.,University of Swansea | Williams A.T.,University of Swansea | Jenkins R.E.,University of Swansea
Geomorphology | Year: 2011

Beach profile surveys, gale climate and atmospheric variations were utilized to assess medium timescale morphological change at South Sands, Tenby, West Wales. Due to beach aspect in relation to offshore islands, gale wave height decreased as wave direction rotated eastwards (r = 0.83) and westwards (r = 0.88). Similarly, wave heights were in attuned to variations in positive (r = 0.68) and negative (r = - 0.72) NAO Index, showing a wave height reduction occurred during weakly negative/positive or transitory phases; morphological change was attuned to atmospheric variation at a 2-year timelag. Shelter from offshore islands is given to waves from the predominant southwesterly direction and was confirmed by negligible correlation with South Sands morphology. However, outside the shelter of these offshore islands, correlation was found between south-eastward rotating wave directions (135°-180°) and morphological change, which resulted in southern and central beach erosion and accretion to the north. With a southwesterly rotation (243°-256°) the opposite was true. Beach rotation expressed by volume change within the sub-aerial zone had a negative phased relationship between beach extremities (r = - 0.94) and a timelagged association within the intertidal zone (r = 0.55). Analyses resulted in the development of two medium timescale rotation models based on incident wave direction and climatic variability. Results have global implications for headland bays in the lee of offshore islands, as well as macro-tidal beach areas; and consequently similar models could inform local, regional and national beach management strategies. © 2011 Elsevier B.V. Source

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