Daily to interannual cross-shore sandbar migration: observations from a multiple sandbar system.

Abstract The most conspicuous characteristic of the cross-shore behaviour of nearshore multiple sandbar systems in sea-dominated settings is interannual net offshore migration (NOM), while that of similar systems in swell-dominated environments appears to be the on/offshore migration in response to individual wave events. Here we analyse an approximately 7.5-year data set (July 1999–February 2007) of daily 10-min time-exposure video images of the swell-dominated double-barred northern Gold Coast, Australia and show that events with wave heights exceeding three to four times the annual average can trigger NOM behaviour similar to that observed elsewhere. During four such events, we observed how the outer sandbar migrated some 75–100 m further offshore than usual and then decayed during slow onshore migration in the subsequent low-energy weeks. The next, moderately high wave event caused the ( ≈ 20 – 30 m / day ) offshore migration of the inner bar to become the new outer bar and the onshore birth of a new bar. Between the large wave events both the outer and the inner bars responded primarily to the seasonal signal in wave height, whereby both bars were located further offshore during the higher (lower) energy winter (summer) months. We suspect that bar size (height and width) may control whether a multiple sandbar system exhibits episodic NOM (as observed here) or interannual NOM. In contrast to interannual NOM, episodic NOM is steered by the order of storm events.

[1]  B. Ruessink,et al.  Coupled and noncoupled behavior of three‐dimensional morphological patterns in a double sandbar system , 2007 .

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

[3]  Kathelijne Mariken Wijnberg,et al.  On the systematic offshore decay of breaker bars , 2010 .

[4]  K. Wijnberg.  Environmental controls on decadal morphologic behaviour of the Holland coast , 2002 .

[5]  Edward B. Thornton,et al.  Bar/trough generation on a natural beach , 1996 .

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

[7]  B. G. Ruessink,et al.  Effect of hydrodynamics and bathymetry on video estimates of nearshore sandbar position , 2001 .

[8]  R. Dean,et al.  Shoreline variability via empirical orthogonal function analysis: Part II relationship to nearshore conditions , 2007 .

[9]  Gerhard Masselink,et al.  Introduction to Coastal Processes and Geomorphology , 2003 .

[10]  Robert A. Holman,et al.  Quantification of nearshore morphology based on video imaging , 2004 .

[11]  Nathaniel G. Plant,et al.  A simple model for interannual sandbar behavior , 1999 .

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

[13]  Extreme Wave Conditions for the South Queensland Coastal Region , 1999 .

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

[15]  S. Elgar,et al.  Wave-induced sediment transport and onshore sandbar migration , 2006 .

[16]  Kathelijne Mariken Wijnberg,et al.  Intersite comparison of interannual nearshore bar behavior , 2003 .

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

[18]  Ian L. Turner,et al.  Coastal Imaging Applications and Research in Australia , 2006 .

[19]  Nathaniel G. Plant,et al.  Practical use of video imagery in nearshore oceanographic field studies , 1997 .

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

[21]  D C Patterson,et al.  Sand Transport and Shoreline Evolution, Northern Gold Coast, Australia , 2024, Journal of Coastal Research.

[22]  Ian L Turner,et al.  A video-based technique for mapping intertidal beach bathymetry , 2003 .

[23]  R. Tomlinson,et al.  Can the gold coast beaches withstand extreme events? , 2008 .

[24]  Roshanka Ranasinghe,et al.  Observations of rip spacing, persistence and mobility at a long, straight coastline , 2007 .

[25]  Giovanni Coco,et al.  Observations of nearshore crescentic sandbars , 2004 .

[26]  B. G. Ruessink,et al.  Multivariate analysis of nonlinearity in sandbar behavior , 2008 .

[27]  J. Trowbridge,et al.  Sand transport by unbroken water waves under sheet flow conditions , 1989 .

[28]  Robert A. Holman,et al.  Quantification of sand bar morphology: A video technique based on wave dissipation , 1989 .

[29]  Ian L. Turner,et al.  CZM Applications of Argus Coastal Imaging at the Gold Coast, Australia , 2004 .

[30]  N. Plant,et al.  INTERANNUAL SHORELINE VARIATIONS AT DUCK, NC, USA , 1997 .

[31]  Michael Blumenstein,et al.  Near-shore swell estimation from a global wind-wave model: Spectral process, linear, and artificial neural network models , 2007 .

[32]  Nathaniel G. Plant,et al.  Prediction skill of nearshore profile evolution models , 2004 .

[33]  Steve Elgar,et al.  Observations of sand bar evolution on a natural beach , 1998 .

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

[35]  John McGrath,et al.  IENCE — A Case Study — The Northern Gold Coast Beach Protection Strategy , 2001 .

[36]  Andrew D. Short,et al.  Single and Multi-Bar Beach Change Models , 1993 .

[37]  Nathaniel G. Plant,et al.  Analysis of the scale of errors in nearshore bathymetric data , 2002 .

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

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

[40]  Steve Elgar,et al.  Wave-Induced Sediment Transport and Sandbar Migration , 2003, Science.