Waves Across Shore Platforms

Lead Research Organisation: Bangor University
Department Name: Sch of Ocean Sciences

Abstract

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Description Analysis of an extensive observational field data set linked to numerical modelling has demonstrated that frictional dissipation of wave energy across rock shore platforms is of secondary importance to dissipation by breaking waves. Frictional dissipation is only significant for very rough, flat platforms during small wave conditions outside the surf zone.

Further work based on the observational field data and numerical modelling has identified that the steepness of the rock platform controls the mechanism of generation of long-period infragravity waves in these environments. Steep platforms show a dominance of the breakpoint forcing mechanism, whereas on more gently sloping platforms the release of the group-bound long wave as incident waves break across the surf zone dominates.
Exploitation Route The findings have implications for the design and implementation of coastal defence structures, indicating that attempts to reduce wave energy are probably best focused on causing waves to break further seaward of the coastline and then dissipating remaining wave energy over wide, flat and rough regions between the breakers and shoreline. These concepts are remarkably similar to coral reef morphology, whereby the waves break on the steep outer reef face, and then dissipation over the reef flat -- our current findings are therefore complementary to parallel research on coral reefs. In the concepts of rock platform morphology, our findings indicate that wave erosion of cliffs in strong tidal environments appears somewhat limited. Under modal conditions the sloping platforms dissipate the majority of wave energy before it impacts the cliff. It is suggested therefore, that cliff erosion is caused by infrequent periodic storm wave impact events, but that erosion of the platform by strong wave orbital velocities, modulated by large tidal ranges, act to maintain the platform gradient. The different infragravity forcing mechanisms are significant since these long period low amplitude waves modulate the water surface elevation at the wave-group frequency. This can permit waves to inundate regions of the rock platform vertically or horizontally above where they would ordinarily exceed, hence effecting ecosystems at higher elevations than ordinarily predicted, and eroding platforms above tidal/incident wave levels.
Sectors Aerospace, Defence and Marine,Energy,Environment,Leisure Activities, including Sports, Recreation and Tourism
 
Title WASP-fielddata 
Description Dataset of wave transformation across 6 UK field sites 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Links with Deltares and TU Delft are directly based on this data, and impact in terms of modifications to models is expected 
 
Description Deltares XBeach links 
Organisation Deltares
Country Netherlands 
Sector Private 
PI Contribution WASP field data is being used to further the development of the XBeach model, which originates from Deltares, into a new environmental setting.
Collaborator Contribution Deltares staff are actively engaged in the modelling process of the collected field data.
Impact Deltares have tied an MSc student from TU Delft to the project. The student will visit Bangor in 2016 to further the collaborations. Austin will act as external examiner to the MSc student at the end of their project.
Start Year 2015
 
Description NOC-L XBeach modelling collaboration 
Organisation National Oceanography Centre
Country United Kingdom 
Sector Academic/University 
PI Contribution Personal collaboration with Jenny Brown based on XBeach modelling. We're taking some ideas and findings developed under WASP into a new Master Research Project on gravel beach erosion, and potentially a NERC ENVISION DTP PhD studentship.
Collaborator Contribution Wider-scale modelling expertise of Jenny Brown at Liverpool extends the capabilities that have arisen from WASP. Particularly linking XBeach with larger-scale boundary forcing shelf-sea models.
Impact One internationally advertised DTP PhD studentship -- shortlisted student currently being assessed at DTP level.
Start Year 2016