12/07/2013

Definitions and context

Bourail, New Caledonia, M.Garcin 2012

o The coast is the interface between ocean and lands in consequence the The driving factors of coastal coast is under the influences of • marine processes Woodroffe 2003 • continental processes evolution • human communities Toward a systemic approach o The coast evolves at different nested timescales : from geological time scale M. Garcin With contribution from (pluri‐millennia), historical time scale G. Le Cozannet New Caledonia, M.Garcin 2012 (centuries, decadal), event time scale (few hours to few days) to physical process (hours, minutes, seconds…)

e.g. Woodroffe 2003, Coco & Murray 2007

Coastal mobility a response to forcing factors • Climate change does not only Raiatéa, French Polynesia, M.garcin 2006 affect sea level but others parameters like : • If, at least a marine or a continental variable – air and sea temperatures, evolves, the coast tempts to adapts to this new – atmospheric and oceanic circulations etc. Coastal retreat condition – all these parameters affect the CL0 CL1 ocean, as well as lands and SL0 : Sea level at t0 • Characterization of the pluri‐decadal coastal SL1 : Sea level at T1 SL1 societies…and thus the coasts Sea Level Rise CL0 : Coastline at T0 mobility is relatively easy, but identifying the SL0 CL1 : Coastline at T1 cause(s) of this mobility is not trivial • Impact of CC to coastline change can’t be reduced to a simple • The present question is: what is (and will be) the mechanistic projection of sea level impact of climatic sea level rise on coasts ? landward The question is: Why it’s impossible to directly assign a new coastline to a given variation of the sea level?

Other External geodynamics processes

Biological processes

Anthropogenic Coastal Climate change actions and changes impacts Forcing Factor: The Climate The 5 main families of forcing factors Internal geodynamics processes

Erosion, accretion, • Coastal changes is transport... driven by 5 main Other External • Evolution of climatic parameters geodynamics categories of factors : processes are spatially highly variable

– Climate Temperature, – Sea level Sea Level, Biological – Others external winds, processes – Temperature storms, geodynamics processes pluviometry... – Salinity and acidity of ocean etc. – Internal geodynamics Coastal Anthropogenic processes Climate change actions and • Others climatic parameters and changes impacts – Biological processes Tectonic, vertical Sea defences, processes acting on the coastal movements, gravels – Anthropogenic actions isostasy... extraction, evolution and impacts mining, Internal daming.... – Dominant winds (trade winds…) geodynamics processes – Storms and Cyclones Intensity and frequency – => even if there remains high uncertainties > => the coast, the forcing factors and related parameters constitute the “Coastal system” on the effects of CC on cyclogenesis > Numerous interactions and feedbacks are existing between factors & attribution of causes – Atmospheric Pressure of coastal changes to one or another factor is complex and difficult Cazenave and Llovel 2010, Stammer, B.Meyssignac, Becker et al. 2012,

1 12/07/2013

Other External geodynamics processes of lateritic soils

Biological processes

Coastal Anthropogenic Climate change actions and changes impacts External geodynamics External geodynamics

Internal geodynamics processes processes processes New Caledonia , M.Garcin 2012 BRGM • CC can potentially modify winds climate (trade winds, storms and cyclones) inducing wave • The CC affects also precipitations (pattern, frequency, intensity) climates change (wave height, orientations, on lands which indirectly modify: frequency…) which modify: – At the watersheds scale – the wave energy during “normal” and extremes • Runoff and surficial erosion of soils Waves generated during the events at coast TC04B cyclone in Sri Lanka (Dec. 2000) • Triggering of landslides (impact on frequency and intensity) – The cross‐shore currents • => inducing indirectly modification the supply of to the – The long‐shore drift currents High during – => can modify the coastal behaviour (erosion  the Xynthia storm stability  accretion) and the level of coastal – Water and sediment discharges of rivers at outlets erosion and flooding hazards at which each • => modification of the sediment supply at the coast and thus the coastal segment is exposed coastal sedimentary budget which can lead to a modification of – The wave climate changes have an the coastal behaviour and mobility (accretionstabilityerosion) impact on the coastline position – likely indirect incidence of rainfall changes on the La Tranche/Mer, France , M.Garcin 2010 coastline position

Other External geodynamics The subsidence effect processes

Biological processes

Coastal Anthropogenic Climate change actions and changes impacts

Internal geodynamics Internal geodynamics processes processes

Morton et al. (2004) Fault Regional • At coast the relative sea level is climatic sea level rise • Vertical movements are not necessarily Local sea level regression composed by: homogeneous at the regional scale or Uplift / Local sea level at T0 – the regional climatic sea level Subsidence Local sea level at T1 even at island scales – vertical movements of ground Regional and local ground movements Uplift – Vertical movements of each site must be • The vertical movements can counteract, compensate or characterized • amplify the climatic sea level rise giving the local relative sea Local sea level transgression Studying the geological and Local sea level at T1 geomorphological context, neotectonic and level Local sea level at T0 seismicity – Vertical movements can be of different origins : • Monitoring the ground movements using Subsidence • tectonic (Tuvalu, Alexandrie, Loyalty islands …), GPS, InSAR etc.. • isostatic (isostatic rebound linked to ice sheets melting : Fennoscandia or Laurentides, hot spot volcanoes…) – Vertical ground movements have consequences for the coastline position • Thermic and linked to the cooling of volcanoes… and coastal hazards (erosion and flooding)

e.g. Mörner 1976, Peltier 2004, Ballu et al. 2011, Wöppelmann et al. 2013 e.g. Wöppelmann et al. 2013

Other External Other External geodynamics geodynamics processes processes

Biological Biological processes processes Example of biological Coastal Anthropogenic Coastal Anthropogenic Climate change actions and Climate change actions and changes changes impacts Example of biological factors: impacts

Internal Internal geodynamics geodynamics processes the reefs processes factors : the reefs

• Reefs play a crucial role in the evolution of • CC induced also an increase of SST and of the acidity of ocean tropical islands as a biological resource, a illustration of the response of reefs to variations in • Reefs are very sensitive to these parameters; exceeding a threshold for sediment suppliers, and a protective barrier Holocene sea level (Woodroffe 2003, 2012) one of these parameters leads to a coral bleaching ...and decreases their against swells and waves during storms and adaptation capacity to accommodate to the sea level rise. cyclones • => What will be the impact on the reefs (barrier and fringing) of SST, salinity and acidity changes? • Climatic parameters like sea level, ocean • What will be the impact of reefs eeoltionvolution on the coastal mobility, on temperature, salinity and acidity are crucial coastal hazards ? for coral reef life – The reefs have been able to accommodate Coral bleaching from 1993 to 2012 (Reefbase Org) the sea level changes during the Quaternary as demonstrated by numerous researchers… – But the remaining question is: what will be the capacity of coral reefs to accommodate in the context of higher rate of sea level rise as predicted in the future decades ?

e.g. Pirazolli et al. 1986, 1988; Bard et al.1990, 1996, 210, Woodroffe 2008, Cabioch 2003, Camoin et al. 2013

2 12/07/2013

Other External geodynamics processes

Biological processes

Coastal Anthropogenic Climate change actions and Example of biological factors : the changes impacts

Internal Biological processes geodynamics mangoves processes

Shells ridge (Mt St Michel France) Six patterns of development in relation • In more temperate seas, biologic Dumbéa, New Caledonia, M.Garcin 2009 to changes in sea‐level Woodroffe 2002 productivity of benthos (bivalves, gastropods…) can be affected by CC • Important role of the in the coastline evolution: role in the rates and protection against erosion and waves during extreme events with incidences on the production of bioclasts • Mangroves are influenced by rises of sea level, CO2, air and water temperatures, Société Géologique et Minéralogique de Bretagne precipitation: pattern, frequency and intensity – This modification of bioclasts production can modify the sedimentary • All these parameters influence the mangroves evolution, what impact on the mobility Shells ridge detail (Mt St Michel budget of bioclastic sandy beach and of coastline ? France) shells ridges Identification of least and most vulnerable world’s mangrove forests – Modifications of the beach resilience to (Alongi 2007) e.g. Plaziat 1995, erosion and in consequence to coastline Woodroffe 2002, Gilman et al. 2006, Done et al. changes. 2006, Alongi 2007 Société Géologique et Minéralogique de Bretagne

e.g. Alongi 2007

Other External geodynamics processes

Biological processes

Coastal Anthropogenic Climate change actions and changes impacts Direct anthropogenic actions Internal Anthropogenic geodynamics processes Wharf • Coastal facilities • Two different types : – Harbours, Wharf, – Direct actions on the coast Nouméa New Caledonia, M.Garcin 2012 – Embankments for roads, railways, – Indirect actions which didn't affect the coastal airports…. system but have an impact on it. Groynes St Vincent Bay, New Caledonia, M.Garcin 2009 – Promenades – Sea side urban facilities… • Direct and indirect actions have impacts on the Pier coastal system, wanted or not…sometime at • The main objective of direct short time and sometimes at longer timescale actions is to “hold the line” – Direct anthrophogenic actions =>direct incidence on the

• Coastal defense works (against erosion or Les Aresquiers , France, M.Garcin 2004 coastal evolution and mobility submersion) Mimizan , France M.Garcin 2013 Varna, Bulgaria, M.Garcin 2013 Revegetation – Hard : breakwaters, dykes, groynes, rip rap, levees Railway embankment Promenade, urban etc. (strategy “hold the line”) Road embankment beach – Soft : revegetation, ganivelles etc… – Intermediate : beach nourishments (strategy “advance the line”) Cap Ferret , France, M.Garcin 2012

Teignmouth UK M.Garcin 2013 Taha, French Polynesia, M.Garcin 2006 Nouméa, New Caledonia, M.Garcin 2009

Other External geodynamics processes

Biological processes

Anthropogenic Indirect anthropogenic actions Coastal Climate change actions and changes impacts Indirect anthropogenic actions

Internal geodynamics processes o Offshore . Dredging of marine sand and gravel decreasing the shoreface • The indirect anthropogenic actions sedimentary stock used during the recovery stage of sandy are various. The feedback effects on Sand extraction coastline coastal zone were generally not o Onshore/offshore wanted or even imagined Devon Energy Corporation, 2006 . Pumping water (e.g. Manila…), petrol and gaz induce ground o At the watersheds scale subsidences with impact on the local relative sea level (e.g. – Hydraulic works within the rivers : ex. Mexico Gulf…) Dams trapping – Extracting sand and gravels in the rivers Tontouta, New Caledonia MGarcinM.Garcin 2009 o The effects of anthropogenic actions can – Changes in the land use and land cover inducing some modification of erosion be summarized as follow : processes ex. : – Modification of coastal sedimentary dynamics Open cast mining » Deforestation, reforestation, crops and fluxes development, urbanization… – Degradation of the functioning of the coastal » open cast mining etc. systems » => Modification of the sedimentary – … all these changes lead frequently to : fluxes in the rivers outlets modifying – the coastal sedimentary budget a loss of coastal resilience to the extreme events… Poro, New Caledonia M.Garcin 2012 Depths and locations of oil platforms in the Gulf of Mexico – a modification of the coastal hazards … » modification of coastal sedimentary (Swordpress in Deep Seas News) budget => potential coastline changes – coastline changes

e.g. Paskoff & Clus‐Auby 2007, Morton et al. 2004, 2007, Garcin et al. 2013 Morton et al. 2004, 2007

3 12/07/2013

Port‐la‐Nouvelle , France 2006 Concluding remarks on forcing factors Pte du Roselier M. Garcin 2012 Teignmouth UK M.Garcin 2013 M. Garcin Huahine French Polynesia M.Garcin 2006

• The number of interacting factors ppyglaying a role on

the coastal dynamics and coastline mobility is largely Cap Breton , France, M. Garcin 2013 enough to explain why the coastal change is highly variable, and why this will remain so... • Moreover, the forcing factors and parameters act on Kogalla beach, Sri Lanka M.Garcin 2009 coasts with highly variable characteristics… THE COASTAL VARIABILITY

Erosion of toe, Huge sand stock counteracting Geomorphological contexts erosion Flat Sandy bay & flat hinterland Sandy beach • 2 main types of coast : accumulating coasts or ablating coasts • Accumulating coasts – Beaches, marshes, , deltas, reefs… – The behavior of a coastal strip can be variable (erosion, stability, accretion)

according to season, year or decades Welligama, Sir Lanka , 2006 M. Garcin

– Reversibility of coastline behaviour, possibility of a recovery phase after Argelès, France, 2006 M. Garcin erosional event, resilience – Sensitivity to cross shore and drift currents, waves, and to Pilat, France, 2012 M. Garcin evolution of the sedimentary budget Muddy Tidal flat Urbanized sand Accretion, stability or erosion

Arcachon , France, 2012 M. Garcin Shaldon UK 2013 M. Garcin M. Garcin

Sandy beach, beach rock and coral pinnacles Beaches with montaneous hinterland and Geomorphological contexts

• Ablating coasts : rocky Stability or erosion coasts and cliffs – Irreversibility of coastline Hikaduwa, Sri Lanka ,M. Garcin 2007 Tautira , French Polynesia M.Garcin 2005 retreat – Importance of the Sandy beach and dune erosion Estuary lithology, fracturation, weathering (humidy and frost) in the evolution of rocky coasts – Sensibility to wave action

Esposende , Portugal M.Garcin 2010 Thio, New Caledonia , M.Garcin 2012 and sea level

4 12/07/2013

Rocky coast (fracturation) Cliff (landslide) Geology and geomorphology conclusion

Pte du Roselier 2012 M. Garcin

Guetary Senix , France, M.Garcin 2006 Biarritz, France M.Garcin 2006 • Same forcing factors applied to different gpggeomorphological and Chalk Cliff (heterogeneous soft rock, Cliff instabilities and engineering works geological contexts: karstic, fracturated) – Various and different effects – Each coastal type have is own resilience and adaptive capacities to evolution of forcing factors like sea level changes – For evaluating the impact of cc on coasts it is necessary to realize a typology the coast taking into account the local geomorphological and geological context – The analysis of past evolutions on each type of coast to a changing sea level is a key for understanding the future behaviour of the coasts La Veulette/Mer, France, 2012 G. Le Cozannet Biarritz , France, M.Garcin 2006

Simplified scheme of processes affecting the shoreline in a Polynesian atoll

SOME EXAMPLES FROM SOUTH PACIFIC ISLANDS…

Erosion, accretion, transport... External geodynamics processes Pluviometry

Sea Level Biological Change, Schematic of a high island winds, processes storms, Simplified systemic graph of pluviometry...

Anthropogenic (New Caledonian example) Climate Coastline actions and coastline mobility of an atoll change mobility impacts

Tectonic, vertical Sea defences, movements, gravels isostasy... extraction, mining, Internal daming.... geodynamics processes

Sea defense, Cyclones / Lagoonal dykes, Climate dependant tropical storms wave climate, embankments... intensity or hydrodynamics External frequence geodynamics Coastal lagoonward Biological Barrier reef erosion Wind accomodation processes Internal geodynamics Coastline Anthropogenic Bioclastic sand OffshoreWave Sedimentary mobility from reef climate budget erosion

SST, acidity, Coraline Sand Vertical Coastal Changes salinity extraction movements (tectonic, thermal, isostatic...) Sea level Relative Topography

5 12/07/2013

Erosion, accretion, transport... External geodynamics processes Pluviometry The caledonian estuaries Sea Level Biological Simplified systemic graph of coastline Change, winds, processes storms, mobility of a high island pluviometry...

Climate Coastline Anthropogenic example change actions and mobility impacts

Tectonic, vertical Sea defences, movements, gravels isostasy... extraction, Sand and • In New Caledonia, analysis of 12 peri‐estuarine mining, Mining Internal daming.... Land use gravel geodynamics activities extractions coastal sites were done processes ‐ 100m • Analysis of the coastline evolution during the 50 Rivers solid Sedimentary ‐ 80m Erosion, discharge at budget at the landslides years have been realized outlets coast Climate dependant • The evolutions of coastline are highly variable Cyclones / Rivers External tropical storms Rainfall discharge from high rate of erosion to high rate of accretion geodynamics intensity or frequence • Analysis of forcing factors and parameters ‐ 60m Biological Sea defense, Wind dykes... (marine, continental and human) were done Internal geodynamics Coastline mobility Coastal OffshoreWave Lagoonal Anthropogenic erosion climate wave climate processes + 78m + 57m + 230m SST, salinity, Barrier and Vertical acidity fringing reefs movements adaptation (tectonic, Coastal Changes thermal, + 300m + 120m isostatic...) Sea level + 318m Relative Topography Mangroves + 300m adaptation

production of nickel ore, Tontouta watershed Conclusion

Erosion of Bare soils and mining Trashs in the • Sea level is «only» one of the forcing factors of coastal evolution watersheds • Interactions (and feedbacks) between processes are numerous • Studies about impact of CC on coastal areas must take into account: • Results show that the coastal evolution the last 5 decades is – global, regional and local parameters, each one influencing the coastal highly related to the % of bare soils generated by open cast Transport behaviour => a multi‐scale approach is a necessity Ni mining on the watershed (Garcin et al. 2013) of thin lateritic – Multi temporal approach : the present and future evolution is linked • An idiindirect anthropogeni c action is the main conttibtiributing Sediment by rivers to the past history and the evolution trend (residual effect of some factor of coastline mobility, during the last 5 decades, while changes in the parameters and processes affecting the coast) the sea level rise and others parameters seem to be of a – Multi disciplinary works are necessary in order to take into account secondary importance the complexity of determining the impact of the CC on coastal systems Coef of determination, R‐ squared = 0.75 Modification – Understanding what could be the future of the coasts in a changing of Others factors Coastal climate imply to take into account all processes acting on their Sediment budget evolutions, a systemic analysis of the problem seems to be a possible approach.

Thanks

6