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
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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
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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
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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
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