Transcript Barrier Beaches

Landforms and terminology in
coastal regions
• the foreshore - the area most
influenced by the high and low
water marks and breaking waves.
• the backshore - submerged only
during the highest tides and
severest storms.
• the berm – the high point on the
beach; the backshore-foreshore
boundary. It changes seasonally.
Landforms and terminology in
coastal regions
Notch
Longshore
bar
Wave-cut
bench
Beach face
Berm
Light versus heavy wave activity
Berm/longshore bar
Light wave activity
Berm grows and
longshore bars shrink
Heavy wave activity
Longshore bars grow
and berm shrinks
Wave energy
Low
High
Time span
Long
Short
Characteristics Summertime beach:
sandy, wide berm,
steep beach face
Wintertime beach:
rocky, thin berm,
flattened beach face
Summertime and wintertime
beach conditions
Summertime beach
Wintertime beach
Movement of sand on the
beach
• Movement parallel (↔) to shoreline
– Caused by wave refraction (bending)
– Each wave transports sand either upcoast
or downcoast
– Huge volumes of sand are moved within
the surf zone
– The beach resembles a “river of sand”
• Erosion
• Deposition
• Human Development
Longshore current and
longshore drift
• Longshore current
= zigzag movement
of water in the surf
zone
• Longshore drift =
movement of
sediment caused by
longshore current
Features of erosional shores
• Headland
• Wave-cut
cliff
• Sea cave
• Sea arch
• Sea stack
• Marine
terrace
Headland
Eastern tip of Oahu
Wave-cut Cliff
Ka‘ula
Sea Cave w/collapsed roof
Na Pali Coast, Kauai
Sea arch
Sea stack
(collapse of
sea arch)
Puu Pehe (Sweetheart Rock)
on the island of Lanai.
Chain of Craters Rd., HI
Sea Arch and Sea Stack
Marine Terrace
Haunama Bay
Features of depositional
shores
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Spit
Bay barrier
Tombolo
Barrier island
Delta
Spit
Barrier Bay
Tombolo
Poipu Beach Park
Kauai
Formation of barrier islands
• Sea level rose
after the last
Ice Age
• Caused
barrier islands
to roll toward
shore like a
tractor’s tread
Barrier Islands
Features:
1. Ocean beach
2. Dunes
3. Barrier flat
4. High salt marsh
5. Low salt marsh
6. Lagoon
Barrier Beaches
Red Sands Beach, Maui
Barrier Islands
Deltas
Feature:
• Triangle deposit of sediment
Mississippi Delta
Nile River Delta
Features of Submerging Shorelines
Changes in Sea Level:
• Tectonic movement
• Isostatic adjustment
• Worldwide (eustatic) changes in sea level
• Ice ages
• Global warming
Composition of Beach sand in
Hawaii:
• Coral
• Shells
• Sponge spicules
• Calcareous algae
• Volcanic particles
White Sand Beach
Black Sand Beach
Big Island
Green Sand Beach
Big Island
Mahana Bay, HI
Red Sand Beach
Maui
1. An abundant supply of
loose sand in a region
devoid of vegetation
2. A wind energy source
sufficient to move sand
grains
3. A topography whereby
sand particles lose their
momentum and settle out
Vegetated dune, Kanaha, Maui. Naupaka shrub and 'aki'aki
and pohuehue (with purple flowers) ground cover at center,
'aki'aki (sparse ground cover) in background.
Close up of 'aki'aki. Photo from
JOHNSTONE, 1997.
Close up of 'akulikuli. Photo
from JOHNSTONE, 1997.
Close up of pohuehue, Honokahua, Maui
Common name: beach morning glory
Sea-Level Rise
Wave/Current Action
Coastal Erosion
Sediment Deficiencies
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Sand mining
Dune grading
Sand impounding (behind shoreline structures)
Water quality degradation
Harbor/navigational channel construction
Types of hard stabilization
• Hard stabilization perpendicular to the
coast within the surf zone:
– Jetties—protect harbor entrances
– Groins—designed to trap sand
• Hard stabilization parallel to the coast:
– Breakwaters—built beyond the surf zone
– Seawalls—built to armor the coast
Shoreline Hardening: Groin
Shoreline Hardening: Groin
Shoreline Hardening: Jetty
Shoreline Hardening: Breakwater
Magic Island is a peninsula shooting off from Ala Moana Park.
The beach is protected by a man-made breakwater that cuts
off the action of the surf while allowing enough water
circulation to keep the salt water fresh and clean.
Shoreline Hardening: Seawall
Waikiki Beach from the Halekulani Hotel.
Lanikai
Lanikai
Beach Replenishment
Kohio Beach
10,000 cubic yards of sand pumped from off shore
Beach Replenishment
Kohio Beach
Beach Replenishment
Kohio Beach
Beach Replenishment
Kohio Beach
Before
After
Beach
Replenishment
Kohio Beach
2006-2007
Before
After
Reasons to Protect Hawaii's Beaches
• Multi-billion dollar visitor economy
• They are critical in flood and erosion
prevention
• They are a part of Hawaii's culture and
heritage.
• Beaches and dunes are important elements
of our shoreline environment and are critical
to the health of the coastal marine
ecosystem.
Inquiry
1. Types of hard stabilization include:_____.
2. Is there a way to slow down erosion without
using hard stabilization?
3. Beach sand from Hawaii is composed of
_____.
4. How is a sea stack formed?
5. What are some key characteristics of plants
living on dunes?