The Dynamic Shoreline. Breaking waves provide the energy that changes the shape and texture of the beach deposits. As waves shoal (touch bottom) in shallow water celerity decreases, wavelength decreases, wave height increases, waves become less stable and refraction occurs.
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Coastal Water MovementWaves generate longshore currents that flow parallel to the beach and rip currents that flow perpendicularly to the beach.
BeachesBeach sediments are moved by currents and waves, especially breakers.
Coastal DunesSand dunes are formed by winds blowing sand landward from the dry part of the beach.
Barrier islands are islands composed of sediment that parallel the coast and form where sand supply is abundant and a broad sea floor slopes gently seaward.
Storm surge is the high water created by the accumulation of wind-blown water against the shore and the mound of water generated by the low atmospheric pressure of the storm.
Impact of People on the CoastlineCoastlines are desirable areas for human habitation, but human activity conflicts with the dynamic state of coastal systems.
Cliffed CoastsA sea cliff is an abrupt rise of the land from sea level.
DeltasA delta is an emergent accumulation of sediment deposited at the mouth of a river as it flows into a standing body of water.
Floods of 1849 and 1850, which caused widespread damage in the Mississippi River Valley, revealed the national interest in controlling the mighty river. Major floods again occurred in 1912, 1913, and 1927. The flood of 1927 was the most disastrous in the history of the Lower Mississippi Valley. An area of about 26,000 square miles was inundated. Levees were breached, and cities, towns, and farms were laid waste. Crops were destroyed, and industries and transportation paralyzed.
Nobody knows exactly how many died in the great disaster. Historians once estimated the death toll at 250 victims, but deaths due to disease and exposure after the immediate flood are hard to tally. John Barry's Rising Tide (1997) estimates that up to 1,000 people, mostly black, died in the Yazoo basin alone. At Mounds Landing near Greenville, for example, a flood surge blew out a dike where thousands of terrified workers were building a bunker of sandbags. Swirling west, the flood ravaged 2.7 acres of farmland before rejoining the mainstem of the Mississippi en route to Natchez and New Orleans.
The Flood Control Act of 1928 authorized work that would give the various basins protection against Mississippi River floods only, although the tributary streams within the basins caused frequent flood damage that could not be prevented by the main stem Mississippi River protective works. Later amendments to this act have authorized work that provides alleviation of the tributary flood problems.
One of the most important modifications to the project was made in 1954 when Congress authorized the feature for the control of flow at Old River to prevent the capture of the Mississippi by the Atchafalaya River.
The U. S. Army Corps of Engineers estimates that the present rate of coastal land loss is 25 square miles a year. The U. S. Fish and Wildlife Service places that figure even higher at about 34 square miles a year. The latter number is based on measuring the loss in coastal land are between 1978 and 1990.
Many areas of the Gulf of Mexico coastline are retreating. If allowed to continue, this retreat can cause irreversible damage to the coastal environment, economy, and quality of life. All Gulf states have serious coastal erosion problems. Parts of Louisiana retreat 65 feet or more per year, while erosion rates of 15 feet year can be found in many other areas of the Gulf.
(1) Sediment Deficit(2) Canals(3) Reclamation (4) Wave Erosion (5) Subsidence (6) Sea Level Rise (7) Saltwater Intrusion
Barrier Island RestorationWetland RestorationMarsh ManagementCanals and Land UseDiversion
The Caernarvon Project diverts fresh water and its accompanying nutrients and sediments from the Mississippi River to coastal bays and marshes in Breton Sound for fish and wildlife enhancement. Benefits include restoration of former ecological conditions by controlling salinity and supplementing nutrients and sediments. The bays are important to oyster production and as breeding areas for shrimp and food fishes, while the marsh areas produce food for fur-bearing animals, alligators, and migratory waterfowl. A total of 16,000 acres of marshland will be preserved and 77,000 acres of marshes and bays will be benefited by the project.
In one way or another, everyone in the nation will feel the enormous loss of land along Louisiana’s coast, and current restoration efforts will only prevent 22 percent of the land loss projected to occur within the next 50 years. However, we know that a comprehensive restoration program, using the Coast 2050 Plan as a guide, could restore and maintain more than 90 percent of the coastal land existing today.
The price tag is $14 billion to construct more than 500 projects that would be needed, but the price of infrastructure alone that would be lost is more than $150 billion.