Tidal Inlets and Tidal Deltas

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Tidal Inlets and Tidal Deltas
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Barrier Coastlines - Galveston, Island
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Barrier Coastlines
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Tidal Inlets a channel of water between
adjacent barriers Inlet formation
formed when the water breaches the island during
a a large storm, such as a hurricane or
northeaster characterized by high a storm surge
and high waves often carved from a surge of
water flowing from behind the barrier towards the
ocean occurs because during a storm surge large
volumes of water are forced into the back barrier
region by overtopping waves, overwash, and inlet
flow. As the storm recedes only the inlet
provides access for the escaping flow. If the
level of water in behind the barrier is high
relative to the ocean side the inlet may be
insufficient to provide drainage and the water
will flow seaward through a weak point in the
island creating a new inlet.
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Tidal Inlets characterized by strong currents,
gt1 m/s capable of scouring deep channels and
efficiently transporting sand offshore of the
inlet, waves continuously lift particles which
then become susceptible to tidal current
transport on the lagoon/estuary side of the
inlet, tidal currents quickly lose velocity as
flow diverges What happens to the sediment?
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Flood and Ebb Tidal Deltas
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Types of tidal deltas Ebb tidal
deltas accumulation of sand on the seaward side
of an inlet formed by the ebb tidal current
mesotidal barrier islands tend to be
drumstick-shaped and have a down drift offset as
a result of refraction around the ebb tidal delta
and local reversals of longshore transport
Flood tidal delta accumulation of sand on the
shoreward sided of an inlet formed by the flood
currents and storm surges flood tidal deltas
become stabilized when salt marshes establish on
them in mesotidal systems, flood tidal deltas
transform into marshland causing the inlet to
migrate to a new position new tidal deltas are
created along the entire area of inlet migration
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Significance of Tidal Deltas tidal deltas are
major sediment sinks, capturing a large amount of
sediment in the littoral system ebb tidal
deltas refract ocean waves, thereby altering the
local littoral dynamics flood tidal deltas aid
in widening the back barrier region allowing the
barrier system to migrate landward
Mesotidal System
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Tidal Deposits Inlets inlet deposits among
coarsest in beach system, including shell
hash trough cross stratification and large
foresets bidirectional transport very mature
sands
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Tidal Deposits Deltas smaller channels in the
tidal deltas top of sequence includes planar
laminated sands, from shoaling-upward swash and
channel margin deposits can include intertidal
marsh, lagoon, and estuarine sediments may
resemble deposits of distributary mouth bar
sequence How do you tell them apart?
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Growth and Migration of Tidal Deltas
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Bolivar Roads Tidal Delta, a Tide Dominated Delta
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