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THE MIQUELON-LANGLADE BARRIER (NW ATLANTIC) Photo : N. Robin

Barrier shoreline evolution constrained by shoreface sediment reservoir & substrate control BILLY Julie PhD Student, CEFREM Laboratory, University of Perpignan, France (*)

ROBIN N.*, CERTAIN R.*, HEIN C.**, BERNE S.* ** WHOI, Fye Laboratory, MA, USA


Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Interest of this study… Literature

This study

Offshore sediment reservoir Formation & evolution coastal system at long time scales

» Comparision at multi-decadal scale (50 yrs): Shoreface sand reservoir (Upper Sand Unit: USU)

Focus: Shoreface volume OR Shoreline

vs Shoreline migration

Interactions are rare but important to quantify

» Weak sediment supply

Sediment-starved systems » Influence of geology (?) Shoreface reservoirs Potential new sediment drivers shoreline evolution ?

Relation(s) or Not ??

12th ICS, Plymouth University, 9th April 2013

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Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Miquelon-Langlade Barrier

Âť 12 km long, Y-shaped mixed sand-and-gravel barrier Âť West coast : Sand dune system Fordunes Beaches Energetic coast; microtidal Photo : N. Robin

12th ICS, Plymouth University, 9th April 2013

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Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Source of sediment Âť Distal to any fluvial source of sediment Âť Local postglacial deposits (retreat Laurentide Ice Sheet) Outwash sand cone Moraines

nowaday

Weak Sand supply

Clay to pebble Sand-poor deposits Evidences at ~ + 45 m high Photo : R. Certain & N. Robin

12th ICS, Plymouth University, 9th April 2013

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Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Shoreface sand reservoir (USU) USU : 0-3 m thick Seismic profile example Up to 13 m depth 1% slope

Up to 17 m depth 0,6% slope

Sand size coarsening landward (0.125 mm mode; 0.1-0.6 mm interval) 12th ICS, Plymouth University, 9th April 2013

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Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Sector A

USU

Shoreline migration (last 50 yrs)

Sector A

Retrogradation Road Progradation

» 1-1.5 km offshore USUA (600 ± 100) m3/lm » Rocky outcrops (2 m high)

lm

linear meter alongshore

» Retrograding system • • • •

Greater exposure to high wave energies Longshore transport southward (Robin 2007) Cross-shore transport limited Sand-poor moraines in amount 12th ICS, Plymouth University, 9th April 2013

Depletion in sediment 6


USU

Shoreline migration last 50 yrs

Road Progradation Stable

Sector B

(< ± 7 m migration)

Progradation

Sector C

Rocky outcrops (2 m high)

» 2-2.5 km offshore

USUB : (1500 ± 200) m3/lm USUC : (1300 ± 200) m3/lm lm

linear meter alongshore

2x USUA

Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Sector B & C

» Not significant migration or slow progradation areas 12th ICS, Plymouth University, 9th April 2013

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Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Sector B & C

USU

Shoreline migration last 50 yrs

Road Progradation Stable

Sector B

(< Âą 7 m migration)

Progradation

Sector C

Longshore transport Southward BUT decreasing

Protected to high wave energies (Cap & Rocky outcrops)

Despite sand availability NOT migration at decadal scale Equilibrium, stability

Longshore transport Northward Slow foredune progradation

12th ICS, Plymouth University, 9th April 2013

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Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Conclusion … » Comparision, the last 50 yrs Shoreface sand reservoir (Upper Sand Unit: USU)

vs Shoreline migration

shoreline closely related to USU retrogradation area

» Weak sediment supply

Barrier : its own source

» Influence of geology (?)

controlled by shallow till bedrock outcrops Affect transport pattern

Relation(s) or Not ??

Good alternative proxy Shoreline monitoring Knowledge of transport patterns strong potential of applicability shoreface sediment availability Needed similar studies comparison 12th ICS, Plymouth University, 9th April 2013

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Julie BILLY, PhD student

12th ICS, Plymouth University, 9th April 2013

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Conclusion + USU Vs Shoreline migration Shoreface reservoir Study area Interest

Sector A

Retrogradation

Progradation Road

Sector B

Stable

Progradation Sector C

12th ICS, Plymouth University, 9th April 2013

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J. Billy SPM Talk ICS 2013