Seasonal morphodynamics of multiple intertidal bars (MITBs) on a meso‐ to macrotidal beach

Abstract

Multiple intertidal bar (MITB) beach systems comprise a succession of subdued, shore‐parallel sandbars, developed under low‐energy conditions in meso‐ to macrotidal settings. Their relatively stable morphologies over long timescales are commonly attributed to a dynamic equilibrium, driven primarily by seasonal morphodynamics. The seasonal behaviour is, however, poorly understood. The relationship between temporal and spatial hydrodynamic forcing and morphological changes was investigated through monthly differential GPS surveys in Dundrum Bay (Northern Ireland) from April 2019 to March 2020, associated with variations in nearshore wave conditions, simulated using the SWAN wave model. During low‐energy summer conditions, southeast waves helped promote MITB stability and a slight increase in bar crest elevation, with the seaward‐most bar buffering and preserving the inner bar system through wave dissipation. In the winter, a progressive increase in wave energy, and a switch in wave direction (southwest to south), initiated the highest rates of cross‐shore bar migration and a lowering of bar crests. While the seaward‐most bar remained largely submerged, the shoreward‐most bar played a key role in protecting the upper‐beach and/or foredune. Winter conditions also forced a newly observed mesoscale longshore drift involving offshore sediment transport in the southwest and onshore transport in the northeast. Cross‐shore variability in MITB behaviour at seasonal timescales was, however, primarily driven by local hydrodynamic conditions, including variations in wave energy and direction. Conversely, alongshore variability was largely influenced by the complex nearshore bathymetry, headlands and an active ebb delta, all interacting with changing hydrodynamic forcing. These results challenge the seasonal equilibrium model for MITB systems and highlight longer‐term patterns of sediment movement.

Monitoring Seasonal Morphobathymetric Change of Nearshore Seafloor Using Drone-Based Multispectral Imagery

“…The only difference here is that this change occurs on a crescentic bar instead to a standard straight bar. This type of across-shore migration has also been reported in the studies of Biausque et al (2022) and Andreeva et al (2021). The bathymetric profile comparison in Fig.…”

“…To our knowledge, there have not been any studies published at present, focusing on bathymetry monitoring using drone imagery. Temporal bathymetry data are required as input to coastal engineering projects for decision-making about dredging or taking counter-erosion measures (Toodesh et al, 2021), wave modelling and sediment transport predictions (Biausque et al, 2022;Jackson et al, 2022). The goal of this study is to capture and quantify small-scale bathymetric features and changes occurring at seasonal scales as a result of nearshore hydrodynamic activity.…”

Introduction to the Women in Geomorphology special issue

“…Field (26) Atkins et al, 2023;Bernatek-Jakiel & Nadal-Romero, 2023;Biausque et al, 2022;Brooks et al, 2022;Bywater-Reyes et al, 2022;Chin, 2022;Gervasi et al, 2021;Glover et al, 2022; Goodman et al, in press;Guiney & Lininger, 2022; Gurnell et al, 2022;Harvey et al, 2022;Hinshaw et al, 2022;Hooke, 2022;Konlechner & Hilton, 2022;Kooijman et al, 2022;Lane et al, 2022;Lefebvre et al, 2022;Marchetti et al, 2022;McKeon et al, 2022;Mol & Grenfell, 2022;Mossa & Chen, 2022;Opalka et al, 2022;Patton et al, 2022;Quock et al, 2022;Regalla et al, 2022;Reitman et al, 2022;Sampietro-Vattuone et al, 2021;Schoch-Baumann et al, 2022;Souza Fonseca et al, 2022;Spiske et al, 2022;Thompson et al, 2022;Uphues et al, 2022;Valentine et al, 2022;Van Soest et al, 2022;Wohl, 2022;Zhang et al, 2022 (Continues)…”

Long‐term drivers of shoreline change over two centuries on a headland‐embayment beach

“…Despite being a comparatively low energy and sheltered beach, with a wide, ultradissipative intertidal beach (Biausque et al, 2020(Biausque et al, , 2022, this system responds to storm events of exceptional magnitude, similar to the 2002 event or the 2013-2014 winter storms.…”