Short-term beach rotation, wave climate and the North Atlantic Oscillation (NAO)

Abstract

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 ¼ -0.67), while cross-correlation at a one-month timelag increased statistical significance (r ¼ 0.84). Due to beach aspect, gale wave heights decreased as wave direction rotated to the south (R 2 ¼ 0.4) and west (R 2 ¼ 0.65), while offshore wave direction influenced change at the southern and northern extremities (R 2 ¼ 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 (R 2 ¼ 0.69 and R 2 ¼ 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 (R 2 ¼ 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.

Mesoscale Morphological Change, Beach Rotation and Storm Climate Influences along a Macrotidal Embayed Beach

“…A storm wave height represented rare events in Tenby area with only 8% of total amount in the 17 years using the methodology proposed by Dorsch et al [42]. This value reflects the wave height at which erosion starts to affect nearby areas, according to previous regional research findings [13,45]. The minimum storm duration was set at 12 h, in this way the storm affected the coast at least during a complete tidal cycle and the lapse time between successive storms was set at one day in order to create de-clustered, independent sets of storms [42,46,47].…”

“…Therefore, 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].…”

“…Many researchers, have documented seasonal or short-term rotations [9,11,13], others have studied rotation at decadal scales [10,[14][15][16]. Thomas et al [12] provided a historic (Centurial) record of beach rotation, influenced by long term shifts in wind directional patterns that caused shoreline displacement resulting in up-drift erosion, down-drift accretion and subaqueous loss.…”

“…Unlike the macrotidal beach work carried out in this research, most rotation studies utilize variations in the location or volume of the subaerial zone to identify shoreline response; this was because almost all were studied in locations with microtidal or mesotidal ranges see for example [10,20,[23][24][25][26][27]. The limited macrotidal research by Stone and Orford [28], Dehouk et al [23], Maspataud et al [29] and Thomas et al [12,13] work within the present area of study also concentrated on subaerial regions. They all highlighted beach rotation despite limited wave exposure.…”

Variabilidade morfológica e granulométrica e balanço sedimentar de uma praia em rotação praial

“…Alguns autores também encontraram relações entre esses eventos de alta energia de ondas e fenômenos climáticos de larga escala como o ENOS -El Niño e Oscilação Sul (Short et al 2000, Short & Trembanis 2004, Anthony et al 2002, Ranasinghe et al 2004, Rooney & Fletcher 2005) e a Oscilação do Atlântico Norte (Thomas et al 2010(Thomas et al , 2011.…”