Coastal Landforms

Beaches• Area of sediment accumulation (sand / gravel)

exposed to wave action along a coast.• Beach morphology controlled by wave action.

foreshorebackshore

duneberm breaker bar

beach face

surf zone

swash andbackwash

zone

berm

shore-parallelridge

(dune)

breakerzone

berm crest

breaker bar

runnel ridge

zone of occasional wavespillover

foreshorebackshore

berm scarpberm

berm crest

breaker bar

widened surfzone

ridge

Beach during moderate wave activity (summer beach)

Beach during storm wave activity (winter beach)

Summer Beach

Winter Beach

Summer Beach• Grows by accreting breaker bars.

Summer Beach• Grows by accreting breaker bars.

Summer Beach• Grows by accreting breaker bars.

Summer Beach• Grows by accreting breaker bars.

Summer Beach• Grows by accreting breaker bars.• Ridge and runnel repair

ridgerunnel

Waves

• Celerity (speed) = L (wavelength) / Time

wavelength

wave base = 1/2 L

Breaking Waves• Water depth < 1/2 L wave “feels bottom”• Wave drags and slows

wave base = 1/2 L

Breaking Waves• C = L / T• If C decreases, L must decrease• If L decreases, wave height must increase (to

conserve momentum).

Breaking Waves• Wave becomes unstable and falls over in

direction of travel - breaks.• Smaller waves may reform.• Water washes onshore as surf and swash.• Water runs back down beach face as backwash.

Wave Refraction

Slower

Faster

Wave bends (refracts) to become nearly beach parallel

Wave crest

swash

back

was

h swash

back

was

h swash

back

was

h

Wave crest

Longshore Current

Longshore Drift

Long Island Sound

Ronkonkoma MoraineHarbor Hills Moraine

Great South Bay

GreatPeconic

Bay

OrientPoint

MontaukPoint

The Necks

Long Beach Jones Beach

Fire IslandHempstead

Plains

N

0 10 20

10 20

KilometersMiles

RaritanBay

Sandy Hook

Limited fetch producingeastward drift

Unlimited fetch producingwestward drift

Bayhead, baymouth and double spit bars

Simple spit

Barrier islands

wave-smoothed shoreSea islands and

tombolos

Cape

Formation of a Spit and Baymouth Bar

Simple spit Complex spit

Double spit

Complex Spit

1 20

0 2 4 6Thousands of feet

Kilometers

GREAT SOUTH BAY

FIRE ISLAND INLETDemocrat

Point

Gilgo and Cedar Beach

Oak Beach

N

1825

1834

1867

1873

188719

11

1919

1928

193619

4019

4519

501959

1960-'75

1945

1914

1873

1887

Lighthouse

1980-'95

Causeway Bridge

Migration of western Fire Island from 1825 - 1995

Barrier Islands

Outer Banks, North Carolina

Barrier Island, Cape Hatteras

Headlands

Headlands erode faster

Formation of a Tombolo

Longshore drift Longshore drift

Tombolo

Bay

beach formationsan

d movementsand movement

Bayhead Beach, California Coast

Eroding coastline, California Coast