On the Intersite Variability in Inter-Annual Nearshore Sandbar Cycles

Dirkjan Walstra, Daan Wesselman, Eveline van der Deyl, BG Ruessink

Research output: Contribution to journalArticleScientificpeer-review

18 Citations (Scopus)
33 Downloads (Pure)

Abstract

Inter-annual bar dynamics may vary considerably across sites with very similar environmental settings. In particular, the variability of the bar cycle return period (Tr) may differ by a factor of 3 to 4. To date, data studies are only partially successful in explaining differences in Tr, establishing at best weak correlations to local environmental characteristics. Here, we use a process-based forward model to investigate the non-linear interactions between the hydrodynamic forcing and the morphodynamic profile response for two sites along the Dutch coast (Noordwijk and Egmond) that despite strong similarity in environmental conditions exhibit distinctly different Tr values. Our exploratory modeling enables a consistent investigation of the role of specific parameters at a level of detail that cannot be achieved from observations alone, and provides insights into the mechanisms that govern Tr. The results reveal that the bed slope in the barred zone is the most important parameter governing Tr. As a bar migrates further offshore, a steeper slope results in a stronger relative increase in the water depth above the bar crest which reduces wave breaking and in turn reduces the offshore migration rate. The deceleration of the offshore migration rate as the bar moves to deeper water—the morphodynamic feedback loop—contrasts with the initial enhanced offshore migration behavior of the bar. The initial behavior is determined by the intense wave breaking associated with the steeper profile slope. This explains the counter-intuitive observations at Egmond where Tr is significantly longer than at Noordwijk despite Egmond having the more energetic wave climate which typically reduces Tr.
Original languageEnglish
Pages (from-to)1-20
Number of pages20
JournalJournal of Marine Science and Engineering
Volume4
Issue number15
DOIs
Publication statusPublished - 25 Feb 2016

Keywords

  • morphodynamic feedback loop
  • Egmond
  • Noordwijk
  • inter-annual bar dynamics
  • process based modeling
  • Unibest-TC
  • sandbars
  • bar switch
  • morphodynamic modeling
  • cyclic bar behavior
  • Jarkus

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