Coastal ProcessCoastal Process

Chapter 9:

Wave DynamicsWave DynamicsWave DynamicsWave Dynamics

• Wave length (L)= Distance between crests, • Wave height (H) = Vertical distance between the crest and the

trough • Wave base = depth below which waves have no effect = ½ *

wave length

Period (T)= Time taken for two successive waves to pass a pointVelocity (V) = L/T

• Breakers form when the sea-bottom is at a depth less than the wave base

• Surf Zone = Zone along which breaking waves collapse

• Swash and backwash = up and down movement of water along the shore line

Sydney, Australia

Notice the surf zone and also the rip currents

Sea-stacks

BeachBeach

Offshore = Farthest out, beyond surf zone

Foreshore = surf zone, tidal flat and swash zone

Backshore = Inwards from Foreshore upto the coastal dunes

Berm

Virginia Keys

What is the direction of the Longshore Current?

• Commenced 1970 s• $62 million over 10 years, 160 K m3 of sand• 18 million m3 of sand dredged and pumped• 200 m wide beach by 1980s

Berm

Swash Zone

Miami Beach

Nature of Coast LineNature of Coast Line

• Active Margin– Western Coast of USA– Steep Continental Shelf– Narrow beach– Rocky cliffs

• Passive Margin– East Coast– Wide, gentle beach, sandy offshore islands– Broad Continental Shelf

Coastal Hazards

• Sea Level Rise

• Hurricanes, Storm surge

• Recognition of coastal hazards

Coastal Erosion

• Human modification has accelarated erosion

• Coastal Engineering structures e.g., sea walls

• Damming of rivers

• Subsidence due to withdrawal of groundwater, oil etc

Spit

Depositional Landforms:•Spits = narrow extension of beach formed by longshore current•Barrier Island = sandy offshore islands parallel to the shoreline

Do you know this place?

Safety concerns

• High elevation (>5 m) above normal high tide• Well developed beach dunes between the site

and the water-line• Overall water level – maximum storm-surge

limit• Emergent or Submergent coast?• Rate of coastal erosion (from USGS and county

maps)