Coastal Geology
Headlands, Beaches, and Sea Stacks
Topics
• Wave refraction
• Sand
• Beaches
• Longshore Drift
• Seawalls and Beach Loss
• Shoreline Features
Topics
• Wave refraction
• Sand
• Beaches
• Longshore Drift
• Seawalls and Beach Loss
• Shoreline Features
Longshore Drift
Longshore Drift
Beaches move
Longshore Drift
Longshore Drift
Many waves do not refract completely
Longshore Drift
Many waves do not refract completely
Approach beach at small angle
Longshore Drift
Longshore Drift
Once a wave breaks, water is moving
toward beach
Longshore Drift
Once a wave breaks, water is moving
toward beach
Water runs up beach face
Longshore Drift
Once a wave breaks, water is moving
toward beach
Water runs up beach face
Carries sand up beach face at an angle
Longshore Drift
Longshore Drift
Gravity pulls water and sand straight
back down beach face
Sand moves in a zig-zag pattern
Kailua
Wai’anae Harbor
Jetties
Shoreline structures
interfere with
longshore drift
Groins
Groins
Groins
Groins trap sand on one side
Groins cause sand starvation on the
opposite side
Waikiki
Waikiki
Sand trapped
Waikiki
Waikiki
Sand starvation
Waikiki
Waikiki
Longshore drift in Waikiki is Ewa
Longshore drift in Waikiki is Ewa
Waikiki
Waikiki
Waikiki
Waikiki
Ma’ili
Pokai Bay
Next
Seawalls and Beach Loss