Interaction of Processes Affecting Shoreline Change

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Interaction of Processes Affecting Shoreline
Change
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Barrier Evolution Models

• Elie de Baumont (1945)
• Wave deposition on an EMERGENT BAR
• Gilbert (1885, 1890) Lake Bonneville, UT
• SPIT ELONGATION in breaker zone
• Merrill (1890)
• Sea-level changes
• Elevating sea floor above MWL to form Barriers
• Emergent Offshore Bar
• McGee (1890) Gulf of Mexico
• Coastal SUBSIDENCE OF SHORE RIDGES

Multiple Modes of Origin (Schwartz, 1971)
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Multiple Modes of Origin

• Primary Barriers
• Engulfed beach ridges
• Secondary Barriers
• Breached spits
• Emergent offshore bars
• Sea level rise
• Seal level fall
• Composite Barriers (combination of I II)

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Different Hypotheses for Barrier Island
Development
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Schematic Diagram of a Barrier Island System
Illustrating the Relationship Among the
Six Interactive Sedimentary Environments
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Barrier Island Beach Ridge Deposits

• U.S.

• East Gulf Coasts
• Arctic Coast of Alaska

• Gulf of Alaska
• Gulf of St. Lawrence

• West Coast Leading Edge Coastline
• East Coast Trailing Edge Coastline,
  i.e. topographic
  asymmetry.
• \Significant supply of sediment from continental
  interior to continental margin, i.e.
• formed low relief coastal plains wide
  continental shelves
• Many modern barriers originally formed as fluvial
  deltas during low-stands in sea-level.

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The Barrier Island System
MAINLAND

• Interacts with barrier by
• Lithology controls recession of lagoonal and
  barrier island shorelines
• Slope (submergence)
• Slope in erosion
• Slope in erosion
• Drainage
• Trellis (relict ridge swales) shore parallel
  trends
• Dendritic headlands, estuaries, shore normal
  trends

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BARRIER PLATFORM

• Stratigraphic substructure of a barrier island
• eg. Pre Holocene topographic high

SHOREFACE

• Upper shoaling breakers
• Lower inner shelf currents and orbital currents
• Important as a sediment source over geologic,
  historic and modern time frames

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BACKBARRIER LAGOON

• Expandable surface area of the H2O surface from
  high to low (vice-versa) tides (Georgia 50
  during springs).
• Mostly composted of fine grained material coarser
  sediment introduced via overwash and flood tides
  and wave energy.

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INLETS AND DELTAS

• Relation between backbarrier lagoons and inlet
  x-sectional area

A nPK
Where n and K are constants P
tidal prism of backbarrier lagoon
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• Bathymetric configurations controlled by
• Inlet currents
• Tidal circulation
• Gravity waves

BARRIER ISLAND

• Major sedimentary environments
• Beach
• Foredunes/secondary, etc.
• Beach ridges
• Barrier flats

• Salt Marshes
• Washover fans
• Subaerial spits
• Tidal flats

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Three-stage Model of Evolution of Barrier
Shorelines Along Abandoned Mississippi River
Deltas
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Sediment Sources

• Coarse Sediments (gravels, ec.) N.E. U.S.
• Spits evolved downdrift of glacial outwash
  deposits, e.g. Cape Cod
• Pre-Holocene deposits (Delaware)
• Inner continental shelf
• Sand
• Primarily from river deltas (Texas)
• Pre-Holocene headlands (new deltaic, N.W.
  Florida)
• Sand and Finer Material Delta switching
  abandonments (Mississippi delta barriers)

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Barrier Migration

• Downdrift
• Onshore
• Offshore

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Recent Mississippi Delta System
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Beach Ridge Development
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Changing Beach Patterns Due to Variations in Wave
Refraction and Sea-Level Fall
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Regressive Sedimentary Sequences Are Dominated by
Beach Ridge Staircases.
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