Analysis of the effects of different storm events on shoreline dynamics of an artificially embayed beach

Abstract

A five-year dataset of Argus-derived mean intertidal positions has been analysed to characterize the shoreface variability in a beach protected by a system of groynes and a parallel low crested structure (Lido di Dante Ravenna, Italy). For the period [2004][2005][2006][2007][2008][2009] 84 intertidal beach bathymetries and shorelines at the zero sea level were used as indicators to assess beach changes in between a number of selected surveys and to determine characteristic patterns of the beach response to storm events from different directions. Variations in the shoreline at the zero sea levels have been quantified and analysed in conjunction with nearshore wave conditions and provenance linked to storm events. These fall into two categories: (1) storm events occurring during Bora (north-eastern) wind conditions and (2) storm events occurring during Scirocco (south-eastern) wind conditions. The results show that, apart from main beach advances of the whole protected beach due to nourishments periodically carried out, a marked variability is observed among the four sub-cells into which the shoreface behaviour has been separately analysed. In particular, a dependence of beach rotation in the 'artificially embayed' area on the substantially bi-directional wave climate has been shown: Bora and Scirocco storm events produce shoreline rotation in counterclockwise and clockwise directions, respectively, due to the occurrence of longshore currents in the opposite direction in the nearshore. An attempt was made to correlate the shoreface dynamics for the main rotation events (14 selected ones) to the wave attack intensity (as the total energy flux due to storm events). A relationship seems to occur (for each storm category) between the shoreline displacements estimated for each sub-cell and the total energy flux computed for inter-survey periods, supporting the occurrence of a link between the observed morphological changes and the hydrodynamic forcing associated with storm events in the five-year monitoring period.

Optimal index related to the shoreline dynamics during a storm: the case of Jesolo beach

“…3). This order of magnitude for the threshold value was the same used in many papers concerning the North Adriatic area, for instance, in Archetti and Romagnoli (2011). In this way, it was possible to create a 1-year long list of storms occurred.…”

“…A suitable parameter for describing and monitoring the impact of storms on the shore (besides being a metric for the achievable income from touristic use) is typically the beach width and its evolution in time (Jimenez et al, 2007;Davidson et al, 2007;Harley et al, 2007;Archetti and Romagnoli, 2011;Archetti and Zanuttigh, 2010). Indeed, the impact of every single storm on the beach may induce short-term (for example, hours to days) morphodynamic responses that can significantly change the shoreline position (Jiménez et al, 2012) and threaten the sheltering function exerted by the littoral zone on the benefit of the mainland.…”

Towards validating a last generation, integrated wave-current-sediment numerical model in coastal regions using video measurements

“…Images taken by four cameras are merged and orthorectified so that they appear like aerial photos and can be used to measure true distances. The resulting time series of video-images have spanned now over seven years and allowed observations on the medium and short-term evolution of the surrounding beaches (Archetti andLamberti 2009, Archetti andRomagnoli 2011). The first camera, pointed to the south, monitored also the beaches between Lido di Dante and the Bevano River mouth.…”

Wave Run-Up Observation and 2dv Numerical Investigation on Beaches Protected by Structures

“…The main cause of error is that the beach steepness and the beach shoreline position are very dynamic. Previous works have quantified the evolution of the intertidal beach shape in Lido di Dante and the shoreline position (Archetti and Romagnoli, 2011) during storms. So in order to have a measure on the beach steepness and shoreline beach position at the beginning of the analyzed timestack, a sort of recalibration on the position of the sea water level and of the steepness of the beach is performed by detecting the intertidal beach bathymetry through a "video-based" algorithm.…”