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Rossbeigh Barrier Beach Investigating the hydrodynamics of a breached barrier beach Michael O’Shea Hydraulics and Maritime Research Centre U.C.C. EGU 2012.

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Presentation on theme: "Rossbeigh Barrier Beach Investigating the hydrodynamics of a breached barrier beach Michael O’Shea Hydraulics and Maritime Research Centre U.C.C. EGU 2012."— Presentation transcript:

1 Rossbeigh Barrier Beach Investigating the hydrodynamics of a breached barrier beach Michael O’Shea Hydraulics and Maritime Research Centre U.C.C. EGU 2012

2 Study Area Dingle Bay, Co Kerry, Ireland Bay enclosed by rocky headlands A 3.2m Spring Tidal Range Waves direction in a narrow band: deg Self Contained Coastal Cell Rossbeigh Inch Cromane

3 Breaching of Rossbeigh Breach in winter 2008 Why study Rossbeigh? Scientific Value – Naturally dynamic coastal system Civic Concern – Flooding, Economic Value, Habitat

4 Similar Morphology Studies on Breaching Barriers Nauset Breach, MA, USA Giese Et al (2009) conducted a re- analysis of the morphological cycle after previous model failed to predict breaching in 2007 Established a 2 Phase conceptual model based on analysis of maps and images from 1800’s to present, regular GPS surveys and water level recording. Slapton Sands & Loe Bar, South West UK (NUPSIG Project) Shingle barrier beach monitoring Numerical Monitoring and extensive measurement system Pre and Post Storm surveys Focus on swash dynamics

5 Monitoring of Rossbeigh Regular Topographic surveys using RTK GPS GIS and Remote sensing : Aerial photography Historical maps Satellite imagery  Identified Centennial morphodynamic cycle  5 million tonnes eroded  Breach widened to 800m  Growth of ebb tidal bars  Realignment of beach

6 Monitoring of Rossbeigh

7 Numerical Modelling Based on low resolution bathymetry and offshore wave data Indication of circulation patterns & wave climate Useful for planning field data campaign

8 Field Work - Objectives Identify drivers of variations in erosion patterns along Rossbeigh Acquire field data to validate a combined Wave, Tidal, Sediment transport and Morphodynamic model

9 Field Work - Wave and Tidal Current Data Collection Vane guided propeller current meters Seabed mounted pressure gauges

10 Results - Tidal Mid Flood Mid Ebb

11 Field Work - Wave 5 onshore locations each for 5 days 1 located 4km offshore continuous for 30 days

12 Results - Wave High tide coincides with largest Hs Convergence of high frequency energy in onshore as waves pass over intertidal bar

13 Direction (degrees) Frequency (Hz) Results – Wave Directionality at High Tide Energy Direction (degrees) Frequency (Hz) Swash AlignedDrift Aligned

14 Results – Tidal Cycle of Rossbeigh Funnelling of waves at drift shore as waves diffract around intertidal bar Sediment in intertidal zone moved towards tidal inlet Tidal current moves sediment offshore on drift aligned into tidal inlet creating a sediment sink Waves become multidirectional on drift aligned as water level rises above bar Drift zone grows as hinge point moves south Tidal inlet transports sediment to offshore bars Funnelled waves moves sediment towards end of Rossbeigh and tidal inlet Low TideMid FloodHigh TideMid Ebb

15 Conclusions Based on limited field data: Erosion rates will continue to be high in the drift aligned zone. The hinge point between zones will continue to move in the direction of the swash aligned zone, increasing the area susceptible to erosive processes described. The risk of coastal flooding and inundation in the back barrier area is increasing

16 Conclusions Present monitoring techniques alone are insufficient to provide definitive conclusions and predictions on future evolution of system Need for novel monitoring techniques focussing on system as a whole rather than single point measurements In HMRC will be trialling : HF wave radar to measure circulation system in Inner Dingle bay Remote operated Helicopter Photogrammetry to map sand bar change Conduct regular shallow water bathymetry surveys

17 Thank You Questions?


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