Abstract
Impacts of storm clustering on beach/dune morphodynamics were investigated by applying the state-of-the-art numerical model XBeach to Formby Point (Sefton coast, UK). The adopted storm cluster was established by analysing the observed winter storms from December 2013 to January 2014 using a storm threshold wave height. The first storm that occurred during this period is regarded as exceptionally intense, and the occurrence of such a cluster of events is very unusual. A 1D model was setup for the highly dynamic cross-shore at Formby Point. After initial calibration of the model parameters against available post-storm profile data, the model was used for the simulation of the storm cluster. It was assumed that no beach recovery occurred between adjacent storms due to the very short time intervals between storms. As a result, the final predicted post-storm profile of the previous storm was used as the pre-storm profile of the subsequent storm. The predicted evolution during each storm was influenced by the previous storms in the cluster. Due to the clustering effect, the bed level change is not proportional to the storm power of events within the cluster, as it would be in an individual storm case. Initially, the large storm events interact with the multi-bared foreshore enabling the subsequent weaker storms to influence the upper beach and lower dune system. This results in greater change at the dune toe level also during less severe subsequent storms. It is also shown that the usual water level threshold used to define dune erosion is over predicted by about 1m for extreme storm conditions. The predicted profile evolution provides useful insights into the morphodynamic processes of beach/dune systems during a storm cluster (using Formby Point as an example), which is very useful for quantifying the clustering effects to develop tools for coastal management.
Highlights
Beach/dune systems which play the role of a natural barrier against coastal inundation are often under threat due to storm-induced erosion (Hanley et al, 2014; Tătui et al, 2014; Harley and Ciavola, 2013; Gómez-Pina et al, 2002; Hanson et al, 2002 and references therein)
The objective of the present study is to investigate the morphological changes of a beach/dune system (Formby Point) under the impact of clustered storm events, which occurred in the 2013/2014 winter period
Morphodynamic predictions of XBeach are sensitive to a number of model parameters (Pender and Karunarathna, 2013; McCall et al, 2010; Lindemer et al, 2010)
Summary
Beach/dune systems which play the role of a natural barrier against coastal inundation are often under threat due to storm-induced erosion (Hanley et al, 2014; Tătui et al, 2014; Harley and Ciavola, 2013; Gómez-Pina et al, 2002; Hanson et al, 2002 and references therein). Examples of storm impact on dunes and on coastal systems for series of events can be found in Karunarathna et al (2014); Ferreira (2005); Callaghan et al (2008); Vousdoukas et al (2012), Houser (2013), Van Enckevort and Ruessink (2003) and Lee et al (1998). Impacts of foredune morphology on the barrier island response to extreme events at Texas were investigated by Houser (2013). Van Enckevort and Ruessink (2003) showed that the temporal scale of bar position fluctuations is related to the storm sequence. Lee et al (1998) found that storm groups of close succession can have a large impact on morphology
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