Coastal Erosion

Characteristics Of U.S. Coasts

• The Pacific Coast - An actively rising margin where indications of recent tectonic activity can be observed.
• The Atlantic Coast - A passive margin on the trailing position of the North American plate.
• The Gulf Coast - Smaller wave size and a smaller tidal range characterize the Gulf Coast.

The Pacific Coast is an active coastline, characterized by relatively narrow beaches backed by steep cliffs and mountain ranges. The major problem is the narrowing of the beaches. Sediment for beaches is interrupted by dams and reservoirs. The coast is actively eroding, and natural sand supply to beaches has decreased. Added to this is storm activity, which further alters the coast.

Atlantic and Gulf Coasts are similar. Development occurs mainly on barrier islands. These islands face the open ocean and receive full force of storms. Development has taken place more rapidly than our understanding of barrier island dynamics

Active Coastlines - Pacific Coast Erosion

Natural processes and human activities do not respect political boundaries. During the 1940s – 1970s, the weather was mild and California saw intensive coastal development. Then, from the mid 1970s – 1990s, the climate shifted to increased storm activity. The El Niño winters of 1977-78, 1982-83 and 1997-98 hit California hard, and the region saw a large amount of coastal erosion. The 1982-83 El Niño episode was the strongest recorded in California. An estimated $116+ million in coastal losses occurred, and 33 homes were destroyed, 3000 homes and 900 businesses were damaged, and $35 million in damages to public recreational facilities. A similar pattern of damages occurred with the 1997 El Niño.

California Coastal Erosion Planning And Response

Coastal Protection Strategies

There are basically two types of strategies: Soft and Hard solutions. "Soft" solutions include beach nourishment while "Hard" solutions include seawalls, joins, etc. In California there are three primary management strategies:

1. Hazard avoidance
• Designing public infrastructure to discourage development in high geologic hazard areas along the coast.
• Creating construction setbacks to reduce the risk to structures in the vicinity of high geologic hazard areas that may be vulnerable to damage.
• Requiring full disclosure rules on real estate transactions in high geologic hazard areas.
• Acquiring and conserving undeveloped coastal property in high geologic hazard areas.
2. Relocation
• Construction setbacks
• Rolling easements - allows structures to be developed but condition their removal to allow for natural coastal processes.
• Creating tax and other incentives when viable & encourage property owners in high-risk areas to relocate out of harm's way.
• Full hazard disclosure rules on real estate transactions in high geologic hazard areas
• Prohibitions against rebuilding damaged structures in high geologic hazard areas.


3. Coastal protection
• Acquiring and conserving endangered or undeveloped property for conversion to public parkland.

Passive Coastlines (Atlantic and Gulf Coasts)

Development in these coastal areas occurs mainly on barrier islands has taken place more rapidly than our understanding of barrier island dynamics. Barrier islands are built of sand dunes that grow in summer and erodes in winter. Vegetation on the island stabilizes dunes and prevents erosion.

Erosion along passive coastlines are caused by human development and storms. One solution the state of Florida has implemented is beach nourishment. Sediment is added to the beaches and natural processes are allowed to move the sand to where it is needed. The image below shows Belleair Beach, Florida, both before and after beach nourishment.


Beach nourishment. can only do so much. Barrier islands are like speed bumps on a road - they are designed to slow down storms. Unfortunately, millions of people have put themselves in harm's way by building on them. The pictures below illustrate why this is not a good idea. First is the waves and/or storm surge. Even if a house is built on stilts, the water will hit the house at the foundation level. Lateral and buoyancy forces push and lift on the home, undermining it's stability. The wind can pry off the rood and then tear the house into pieces.
The next set of images show the erosion and shoreward migration of a beach in North Topsail Island in North Carolina. The first is after Hurricane Bertha on July 16, 1996, the next after Hurricane Fran on September 7, 1996, and the last after Hurricane Bonnie on August 28, 1998.

Coastal Zone Management

Federal Efforts
The Coastal Zone management Act of 1973 was passed to support state efforts to reasonably manage coastal development. This was followed by the Flood Insurance Act of 1973, which requires mapping and avoidance of coastal hazards. The program has not worked well and owners are rebuilding in sites of homes destroyed by storms.

California State Efforts The Coastal Initiative was passed in 1972. Later, the state passed the California Coastal Act and established the Coastal Commission in 1976. Both acts limit new coastal construction and development.

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