Coastal Environmental Geology

Environmental Issues and Coastal Geology

• Excessive Sedimentation

• Shoreline Erosion

• Coastal Subsidence

• Sea Level Rise

• Storm Surges

• Tsunamis

Wave Motions

• Particles in a wave travel circular paths• The water in a deep-water wave does not

move forward• Below wave base, wave effects are negligible

The Highest Recorded Ocean Wave

When Waves Meet the Shore

When the bottom interferes with wave motion, the wave steepens and the top overtakes the bottom.

Wave Refraction

• Waves change path when they reach shallow water

• Wave energy is concentrated on headlands and spread out in bays

Rips

• When waves break parallel to a beach, rips occur

Rips, Lake Superior

Excessive SedimentationNatural Sedimentation

• Rarely an issue; Nobody complains about too much beach

• Siltation of harbors and channels

Artificial Sedimentation

• Smothering of Marine Communities and Wetlands

Shoreline Retreat

Shoreline Erosion

• Sediment Starvation

Coastal Subsidence

• Compaction

• Sediment Starvation

Sea Level Rise

• Thermal Expansion

• Glacial Melting

Shoreline Retreat, Wisconsin

Beach Erosion, Surfside, Texas

Beach Erosion, Surfside, Texas

Beach Erosion, Surfside, Texas

In the long run, nothing is as futile as trying to resist

shoreline change.

Change can be resisted for a while, but when the water wants

something badly enough, it will come in and take it.

Property Values and Shoreline Erosion

• If more than half the original lot is left, it’s Location, Location, Location

• After that, it becomes obvious there soon won’t be any location left

Longshore and Beach

Drift

• Most Beach Sand Is Created by Weathering and Carried to Coasts by Rivers

• Beach Sand Moves along the Coast by Longshore and Beach Drift

Beach Drift

Beach Drift, New Jersey

Catastrophic WavesStorm Surges

• Galveston 1900 (6000-8000 dead)

• Bangladesh 1970 (300,000 dead)

• Bangladesh 1991 (140,000 dead)– Operation Sea Angel

• Katrina 2005 (1300 dead)

Tsunamis

• Indian Ocean 2004 (250,000 dead)

Bangladesh Annual

Flooding

Bangladesh Cyclone Hazard

Hurricane Evacuation

Marker

Storm Waves: Galveston, Texas, September 8, 1900:

• 6000-8000 dead

• 3600 houses destroyed

Raising Galveston – 6 in. to 17 ft.

“A rickety maze such as Dr. Seuss might have drawn”

The Lift in Progress

Pumping in the Sand

The Galveston Seawall

Seawall, Galveston, Texas

Seawall, Galveston, Texas

Centennial Monument

Seawall Model, Galveston, Texas

Raised Hotel, Galveston, Texas

Seawall Buffer, Galveston, Texas

Seawall, Galveston, Texas

Beach Growth, Galveston, Texas

Any Port in a Storm?

The Decline of Galveston• In 1900, Houston and Galveston were

comparable in size

• It took years for Galveston to recover

• The East Texas oil boom happened during the recovery and bypassed Galveston

• Business and shipping relocated to Houston

• Galveston 60,000

• Houston 1.6 million

Katrina, 2005

Coastal Wetland, Louisiana

Mississippi River Levee

Mississippi River Levee

Levee and French Quarter

New Orleans

Katrina Flooding

Katrina Flooding

The Katrina Disaster• Could have been much worse

– Storm weakened before landfall (5 to 3+)– Eye passed east of New Orleans– Many levees failed after peak of storm

• Predictable Disaster• Poor Individual Preparedness• Unrealistic Expectations• Media Sensationalism• Insufficient FEMA Authority

Coastal Subsidence in Louisiana• Compaction of sediment

– Formerly offset by new sediment– Interception of sediment by dams– Delta buildup far offshore– Atchafalaya diversion?

• Sea Level Rise

• Oil drilling?

Neglected Factors in Louisiana• Atchafalaya sedimentation

– 6.5 km2 per year– Channel dredging needed– Concern over loss of wetlands

• Mississippi is long overdue to shift to the Atchafalaya– Before locks, 1/3 of Mississippi being diverted– Diversion will starve other areas of coast –

naturally• No amount of sediment will raise New Orleans

The Great Tsunami

December 26, 2004

Banda Aceh

Waves Approaching Sri Lanka

Waves Hitting Sri

Lanka

Wave Height and

Travel Time