Consequences of short-term changes in coastal processes: a case study

In 1997-98, unique critical beach erosion led to structural failure along the Penarth, South Wales UK coastline and anthropogenic activities, such as the construction of the Cardiff Bay Barrage and offshore marine aggregate dredging, were suggested as causes. The time-frame of significant erosion was between 1995 and 1997 and forcing agents (extreme sea level and wind direction) and shoreline indicators (mean beach level and MHW) were analysed in order to assess change. Water level analysis showed that although there was no significant difference between actual and predicted mean sea levels, extreme sea levels at that time were significantly higher (t = 3(.)305; d.f. = 8; p < 0(.)05). Three wind direction analyses (annual mean, mean annual maximum gust and mean annual maximum gust >= 28 kn) between 1995 and 1997 also showed significant differences (p < 0(.)05). All comprised more easterly components which meant they approached the beach from the sea. Furthermore, gusts >= 28 kn from the northeast quadrant, that is, 0 degrees to 90 degrees true, were significantly more frequent during these years (t = 3(.)674; d.f. = 8; p < 0(.)01). Justification of statistical significances was established and there was supporting evidence of unusual meteorological conditions at that time. Relationships showed correlation between forcing agents (extreme sea level and wind direction) and shoreline indicators (mean beach level and Mean High Water). Furthermore, regression analysis showed winds from the northeast quadrant resulted in steeper longshore gradients, as a consequence of beach material loss. Therefore, it was concluded that the critical erosion of Penarth beach between 1995 and 1997 was caused by increased wave attack from the northeast and southeast quadrants, generated by unique significant changes in wind direction and extreme sea levels. Copyright (c) 2008 John Wiley & Sons, Ltd.