THE WINTER STORMS OF 2013/14: OCEANOGRAPHY AND COASTAL IMPACTS Gerd Masselink, Plymouth University

Coastal Futures 2015 OUTLINE

• Wave conditions during 2013-2014 winter • Pictorial overview of storm impacts in SW • Regional overview of coastal response in SW England • Coastal response on the North coast – • Coastal response on the South coast – Slapton Sands • Conclusions WINTER STORMS OF 2013/14 Measured and modelled wave heights

12 10 8 6 4 2 0 Dec13 Jan14 Feb14 Mar14 Apr14

14 m 12 m

Hercules 06/01/14 Petra 05/02/14 Comparison 2013/2014 winter with 60-year wave record

8-week running mean wave height 4 3 2 1 0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 PHOTOGRAPHIC OVERVIEW OF IMPACTS Southwest coast of England

North coast Hercules W

South coast Overwash gravel ridge at Westward Ho!, North Devon Destruction of rock arch, , North

Before Hercules After Hercules Removal of beach,

Before Hercules After Hercules Destruction of sea defence, Fistral Blu bar, Beach erosion, Perranporth, North Cornwall

End of summer 2013

After Hercules Removal of Monkey House, Porthreath, North Cornwall

Before Hercules After Hercules Southwest coast of England

North coast

South coast Petra SW Coastal flooding, , South Cornwall Coastal flooding, , South Cornwall Beach lowering, Seaton, South Cornwall Hot Wok Restaurant, Plymouth, South Devon Dune erosion, Thurlstone, South Devon Removal of beach in Torcross, South Devon

EndBefore of summer

DuringDuring Petra Removal of beach in Torcross, South Devon

EndBefore of summer

AfterDuringAfter Petra Gravel on road, Slapton Sands, South Devon

Before Hercules After Hercules Damage to SW railway line, Dawlish, South Devon

Cost: £1M per day to the SW economy COASTAL IMPACTS – REGIONAL OVERVIEW SW England and PCO beach monitoring sites

North coast

W

South coast SW Beach monitoring (> 30 beaches, >200 profiles) Storm impacts along coast of SW England – per profile

BRISTOL CHL NORTH COAST SOUTH COAST

/m)

3

Accretion

Erosion Change sediment Change volume (m line in profile Beaches geographically arranged from to SW England and beach monitoring sites

Bristol Channel

North coast

W St Ives Chesil

SW South coast COASTAL IMPACTS – NORTH COAST Perranporth Impact of Hercules on Perranporth

North coast

W

South coast Perranporth beach in summer Perranporth response from LiDAR (Hercules) Wave approach

Erosion (> 2m ) Accretion (> 2 m) Where has the sand gone?

Offshore accretion

Mega-rip channel Intertidal erosion

Erosion (> 2m ) Accretion (> 2 m)

High tide Low tide Offshore sand model – North coast

Before the winter After the winter dune Dune scarp

Thin beach Rocks exposed

Sand bar below low tide Storm response and Westward Ho! from LiDAR

Wave approach

Erosion (> 2m ) Accretion (> 2 m) COASTAL IMPACTS – SOUTH COAST Slapton Sands Impact of Petra on Slapton Sands

North coast

South coast SW Gravel beaches of Start Bay, South Devon

Blackpool Slapton Sands Sands Beesands

North Hallsands

South Hallsands Slapton response from RTK-GPS (Petra)

before storms after storms P19

P11

Wave P0 approach 3

Sediment volume change (m /m) Torcross Alongshore variation in storm response approach Wave Distance from Car Car park Erosion Torcross (m) Accretion Strete gate Angle of breaking waves during Petra on Slapton Sands Longshore sand model – South coast

Before the winter After the winter rocky ‘new’ headland beach

beach widening beach narrowing

lagoon lagoon Storm response and Exmouth from LiDAR

Wave Erosion (> 2m ) approach Accretion (> 2 m) CONCLUSIONS • Storm waves are related to Atlantic low pressure systems – the storm frequency, intensity and tracks will be affected by climate change • The 2013/2014 winter was the stormiest winter since 1950

• 1% exceedence Hs was exceeded by 20 storm events • 10 storms with peak Hs > 8 m • 2 storm with peak Hs > 10 m • Storm impacts show a large geographical variability • North coast = offshore sediment transport and beach erosion • South coast = longshore sediment transport and beach rotation • Coastal response is strongly related to the storm-wave direction • Beach sediment has not ‘disappeared’, but has been transported elsewhere (in nearshore bars, along the beach, around the corner) • Beach recovery during the spring and summer 2014 has been limited • Incomplete recovery leaves beaches vulnerable to further erosion • Remedial action must be informed by understanding of the processes obtained from monitoring – state-funded organisation such as the PCO play a key role LONG-TERM CONTEXT Waves and beach volume Perranporth since 2006

2013/2014 winter Waves and beach volume Slapton Sands since 2007 2013/2014 winter

P18

P5 – south end P5

P18 – north end