Coastal Processes

Objectives

• Examine Physical Properties of Waves• Examine behavioral changes of waves

approaching coast• Explain the role of waves in sediment erosion,

transportation and deposition• Discuss tides and their role in coastal erosion

and deposition• Discuss effects of storms and crustal

movement on coastal landscapes.

Coastal Processes

• Shape the landscapes along the coast– Must understand processes shaping coast

• Impact humans– More and more people moving to coast– Coastal areas heavily developed

• Must learn to manage coastal areas• Knowledge of coastal processes is management key

Waves

• Most important agent in shaping coastal landforms

• Size of waves depends on:– Velocity– Wind persistance– Fetch

Garrison, Oceanography An invitation to marine science

Wave Properties• Height = vertical distance from crest to trough • Wavelength = horizontal distance between

successive crests or troughs• Wave period = time required for two successive

crests to pass a fixed point

Motion in Deep Water Waves• Motion is orbital• Waves with orbital particle motion termed waves

of oscillation• Particle motion ceases at ½ wavelength

Waves Against the Shore• Swells shoal as approach coastline

– Feel bottom at ½ wavelength– Wavelength decreases– Wave height increases– Wave particle motion becomes elliptical– Wave breaks– Swash and backwash move on beach

Wave Refraction• Bending of waves as

they approach coastline– Part of wave in

shallow area slows

– Part of wave in deeper area continues with higher speed

• Results in longshore current

Erosion of Coastal Headlands• Wave refraction

concentrates energy on headlands

• Sand accumulation occurs in lower energy bays

• Results in straightening of coastline

Shore Zone Currents—Rip Currents• Rip Currents

– Strong narrow currents moving from beach to ocean

– May be identifiable through interruption of breakers and muddier sediment moving seaward

Shore Zone Currents—Longshore Currents

• Currents moving along the coast set up by wave refraction

Longshore Drift• The movement of sediment

along the shoreline by longshore currents

• Beach drift is movement of sediment on the beach – Swash moves sand at an

angle up beach – Backwash swash moves

sand down the beach• Groins and other structures

used to interrupt drift and stabilize beaches

Tides• High and low tides tend to

widen beaches• Tidal range is greatest in

estuaries, bays, and lagoons

• Erode and deposit sediment– Erosion occurs in

narrow rocky bays with great tidal ranges

– Where currents slow down deposition takes place

Tides

Storms

• May modify coastal areas in short period• Storm surges plus low atmospheric pressure

result in increased sea level– Wave aggressively attack coastal features– High tides aggravate conditions

Crustal Movements

• Influence development of coastal features• Tectonic activity leads mostly to raising and

erosion of coast– California, Oregon, & Washington are examples

• Some coastal areas are sinking due to accumulation of sediment– Texas and Louisiana are examples