Coastal Regions and Land Loss

Chapter 10

Morris Island Lighthouse, SC

Coastlines

Active vs. passive marginsPopulation concentration

• Seven of 20 largest US cities on or near coastline

• 53% US population lives in coastal counties

Deep-water wave form (water depth > 0.5L)

Factors controlling waves

1. Wind speed2. Duration3. Fetch

Plunging breakers

Spilling breakers

Coastal erosion along beach at Santa Barbara, CA

Longshore drift and transport

Sea level changes

Eustatic sea level rise caused by• Changes in amount of water in oceans

Short-term• Changes in shapes and volumes of oceans

Very long term Related to sea floor spreading

Climate is major control• Thermal expansion or contraction of water

Shoreline conditionsEmergent

• Earthquakes and uplift/downdrop• Glacial rebound• Area: New England

Submergent• Higher sea level• Irregular shorelines common• Area: Mid-Atlantic area – Chesapeake Bay

(VA)

Very short-term changes

Storm surgesChanging tides

• Extreme: Bay of Fundy, eastern Canada• 15 m tidal range twice daily

• Normal daily changes (2 high, 2 low)

Coastal erosion rates

Note changes based on shoreline typelow coastlines most affected

Minimizing coastal hazards

Hard stabilizationSeawalls: concrete, large blocks

Cause more problems than they solve; they enhance beach erosion

n Groins: built perpendicular to shoreline

n Problem is the area down drift from groin is not fully replenished

n Fix by beach nourishment

Chesil Beach on southern coast of England

Breakwaters

Built to protect shoreline by intercepting waves

Jetties

Usually pairs of protrusions

Note beach modifications

Soft (beach) Stabilization

Moving sand around, usually from offshoreTemporary solution due to dynamicsMust be repeated

Managed “retreat” solution

Prevent buildingRelocate threatened buildings

Miami Beach, FL24 million cubic yards over 10 years

Before beach nourishment After beach nourishment

Cape Hatteras lighthouse

Built 500 m from water Later moved 850 m inland