Dynamics of single-barred embayed beaches

Abstract The dynamics of single submerged sandbars of two artificial embayed beaches (La Barceloneta and Bogatell, Barcelona, NW Mediterranean) has been studied with a video-recorded data set of 4.3 years. The alongshore-averaged cross-shore migration, the orientation with respect the shoreline and the sinuosity of the barlines have been analyzed and related to wave conditions, alongshore sediment transport and shoreline variability. In general, the submerged bars follow the general cyclic morphological behaviour observed in natural beaches, switching among the four intermediate morphodynamic states, but the studied beaches can be arrested during long periods of low wave conditions. The dominant up-state transition in Barcelona beaches during storms is the transition toward the rhythmic bar and beach state, the complete morphodynamic reset (longshore bar and trough state) only occurring during extreme wave events. The cross-shore migration of bars is dominated by the weekly and interannual components. The interannual component shows an onshore bar migration trend at both beaches, in contrast with the net offshore migration observed in multibarred open beaches. Bar disposition is located progressively seaward in the dominant alongshore transport direction (i.e., oblique with respect to the shoreline). At La Barceloneta beach, shoreline and barline orientations change consistently and a significant correlation between the accumulated alongshore sediment transport and the associated change in bar orientation has been found, suggesting that alongshore transport can play a significant role in barline orientation. Finally, bar sinuosity increases during eastern storms in both beaches. This indicates that the formation of crescentic bars occurs for approximately shore-normal waves. Some of the differences observed in bar morphology and mobility in the two studied beaches are related to their different level of protection with respect to the incident waves (beach indentation).

[1]  Jorge Guillén,et al.  Morphodynamic response of a two-barred beach to a shoreface nourishment , 2008 .

[2]  Brian Greenwood,et al.  Sediment supply from shoreface to dunes: linking sediment transport measurements and long-term morphological evolution , 2004 .

[3]  R. Holman,et al.  Storm-induced response of a nearshore-bar system , 1985 .

[4]  J. Barusseau,et al.  MORPHOSEDIMENTARY MULTIYEAR CHANGES ON A BARRED COAST (GULF OF LIONS, MEDITERRANEAN SEA, FRANCE) , 1994 .

[5]  R. Holman,et al.  Morphodynamics of intermediate beaches: a video imaging and numerical modelling study , 2004 .

[6]  Aart Kroon,et al.  Barred beaches , 2002 .

[7]  J. Guillén,et al.  Longshore bar and trough systems in a microtidal, storm-wave dominated coast: The Ebro Delta (Northwestern Mediterranean) , 1993 .

[8]  Yoshiaki Kuriyama,et al.  Medium-term bar behavior and associated sediment transport at Hasaki, Japan , 2002 .

[9]  D. Bowman,et al.  Bar morphology of dissipative beaches: An empirical model☆ , 1983 .

[10]  B. G. Ruessink,et al.  Morphodynamic response of nearshore bars to a shoreface nourishment , 2005 .

[11]  A. Brad Murray,et al.  High‐angle wave instability and emergent shoreline shapes: 1. Modeling of sand waves, flying spits, and capes , 2006 .

[12]  B. Ruessink,et al.  Onshore sandbar migration at Tairua Beach (New Zealand): Numerical simulations and field measurements , 2008 .

[13]  G. Różyński.  Data-driven modeling of multiple longshore bars and their interactions , 2003 .

[14]  Kathelijne Mariken Wijnberg,et al.  Extracting decadal morphological behaviour from high-resolution, long-term bathymetric surveys along the Holland coast using eigenfunction analysis , 1995 .

[15]  Nathaniel G. Plant,et al.  Role of morphologic feedback in surf zone sandbar response , 2001 .

[16]  Donald G. Bailey,et al.  An Inter-Site Comparison of Net Offshore Bar Migration Characteristics and Environmental Conditions , 1999 .

[17]  Joaquín Tintoré,et al.  Morphodynamic classification of sandy beaches in low energetic marine environment , 2007 .

[18]  A. Short.  Rip-current type, spacing and persistence, Narrabeen Beach, Australia , 1985 .

[19]  Daniel Calvete,et al.  Morphological development of rip channel systems: Normal and near‐normal wave incidence , 2005 .

[20]  R. Holman,et al.  The history and technical capabilities of Argus , 2007 .

[21]  Francesca Ribas,et al.  Assessing the Suitability of Video Imaging for Studying the Dynamics of Nearshore Sandbars in Tideless Beaches , 2010, IEEE Transactions on Geoscience and Remote Sensing.

[22]  T. Aagaard.  Nearshore Bar Morphology on the Low-Energy Coast of Northern Zealand, Denmark , 1988 .

[23]  Nathaniel G. Plant,et al.  On cross‐shore migration and equilibrium states of nearshore sandbars , 2010 .

[24]  Roshanka Ranasinghe,et al.  Rip spacing and persistence on an embayed beach , 2006 .

[25]  Jorge Guillén,et al.  Comment on the article "Morphodynamic classification of sandy beaches in low energetic marine environment" by Gómez-Pujol, L., Orfila, A., Cañellas, B., Alvarez-Ellacuria, A., Méndez, F.J., Medina, R. and Tintoré, J. Marine Geology, 242, pp. 235-246, 2007 , 2008 .

[26]  B. G. Ruessink,et al.  The behaviour of a multiple bar system in the nearshore zone of Terschelling, the Netherlands: 1965–1993 , 1994 .

[27]  Jorge Guillén,et al.  Shoreline dynamics and beach rotation of artificial embayed beaches , 2008 .

[28]  B. G. Ruessink,et al.  Video observations of nearshore bar behaviour. Part 1: alongshore uniform variability , 2003 .

[29]  J. Guillén,et al.  Monitoring beach nourishment based on detailed observations with video measurements , 2006 .

[30]  Ian L. Turner,et al.  Daily to interannual cross-shore sandbar migration: observations from a multiple sandbar system. , 2009 .

[31]  L. Wright,et al.  Morphodynamic variability of surf zones and beaches: A synthesis , 1984 .

[32]  H. Schuttelaars,et al.  Morphodynamic evolution of double-barred beaches , 2006 .