Lake Pontchartrain
Lake Pontchartrain is an estuary located in southeastern Louisiana in the United States. It covers an area of with an average depth of. Some shipping channels are kept deeper through dredging. It is roughly oval in shape, about from west to east and from south to north. As an estuary, its “Lake†title is a misnomer, but only a slight one, as its passage to the open sea is narrow.
In descending order of area, the estuary is located in parts of six Louisiana parishes: St. Tammany, Orleans, Jefferson, St. John the Baptist, St. Charles, and Tangipahoa. The water boundaries were defined in 1979.
The estuary is crossed by the Lake Pontchartrain Causeway, the longest continuous bridge over water in the world. A power line also crosses the estuary. Its towers stand on caissons in Lake Pontchartrain, and its length can be used to visually demonstrate the curvature of the Earth.
Toponymy
Lake Pontchartrain was named for Louis Phélypeaux, comte de Pontchartrain. He was the French Minister of the Marine, Chancellor, and Controller-General of Finances during the reign of France's "Sun King", Louis XIV, for whom the colony of Louisiane was named.The name Pontchartrain itself comes from the place in France where Phélypeaux's château was situated. It is thought that this name originates from it being where a bridge crossed the river Mauldre on the ancient route from Lutèce to Chartres.
Lake Maurepas, directly west of Lake Pontchartrain, was named for Phélypeaux's son, the comte de Maurepas, who was also a French statesman.
Description
Lake Pontchartrain is an estuary connected to the Gulf of Mexico via the Rigolets strait and Chef Menteur Pass into Lake Borgne, another large lagoon, and therefore experiences small tidal changes. It receives fresh water from the Tangipahoa, Tchefuncte, Tickfaw, Amite, and Bogue Falaya rivers, and from Bayou Lacombe and Bayou Chinchuba. It is one of the largest wetlands along the Gulf Coast of North America. It comprises more than 125,000 acres of wetland, including bottomland hardwoods and cypress swamps, along with a complex mixture of herbaceous wetlands including fresh, intermediate, and brackish marsh. Lake Pontchartrain itself is part of the larger Pontchartrain Basin, a 10,000 square mile watershed that includes 16 Louisiana parishes and 4 Mississippi counties. The Basin is one of the largest estuarine systems of the Gulf of Mexico. The Pontchartrain Basin includes Lake Pontchartrain and the drainage area of its tributary streams, Lake Maurepas and the drainage area of its tributaries, The Rigolets, Lake Borgne, the Biloxi Marsh and Chandeleur Sound.Salinity in Lake Pontchartrain varies from negligible at the northern cusp west of Mandeville up to nearly half the salinity of seawater at its eastern bulge near Interstate 10. Lake Maurepas, a true freshwater lake, connects with Lake Pontchartrain on the west via Pass Manchac. The Industrial Canal connects the Mississippi River with the lake at New Orleans. Bonnet Carré Spillway diverts water from the Mississippi into the lake during times of river flooding.
History
The lake was formed 4,000 to 2,600 years ago as the evolving Mississippi River Delta formed its southern and eastern shorelines with alluvial deposits.Human habitation of the region began at least 3,500 years ago. One recorded Indigenous name for the lake is Okwata.
Habitation increased rapidly with the arrival of Europeans; in 1699, French explorer Pierre Le Moyne d'Iberville renamed the Lake Pontchartrain after Louis Phélypeaux, comte de Pontchartrain.
In 1777, the American naturalist William Bartram explored the north shore during a trip west.
In 1852, a railroad was constructed to link New Orleans to the north. Engines turned at Pass Manchac. However, the pilings were burned to the water line in the Civil War.
During the early 20th century, the great cypress swamps of the area were heavily logged and many have not regrown.
After over 30 years of oil drilling had yielded just 12 million barrels of oil and condensate and 119 billion cubic feet of natural gas, and caused major pollution of the lake, the State Mineral Board enacted a moratorium on oil drilling. As of 2009, there were 4 active wells continuing prior leases, and 25 derelict wells. According to the Louisiana Department of Environmental Quality, they and the US Coast Guard see at least one oil spill per day in Louisiana's wetlands. Estuarine wetlands are among the highest on the Environmental sensitivity Index.
Conservation and restoration
Oil drilling and other exploitation stresses the lake's ecosystems. Marshes, for example, are turning to open water, and cypress swamps are being killed by saltwater intrusion. However, brown pelicans and bald eagles, once scarce, were a common sight along the shores as of 2004. A team of experts assembled by The Nature Conservancy assessed the situation in 2004 and identified seven target habitat types in particular need of conservation management: bottomland hardwood forest, cypress swamp, relict ridge woodland, fresh/intermediate marsh, brackish/salt marsh, lake open water, and littoral submersed aquatic vegetation. The bottomland hardwood forest and cypress swamp are suffering from a lack of freshwater input and sediment deposition owing to the levees upstream from the lake. In addition, bottomland hardwoods are being invaded by exotic species such as Chinese tallow, while freshwater marshes are being invaded by exotic species such as elephant's-ear. The team identified four key animal species which could indicate the degree to which the system declines or improves. These were the rangia clam, gulf sturgeon and paddlefish, and the alligator snapping turtle.The future of the lake depends, in part, on restoring annual spring floods to the wetlands of the lake basin and controlling urban sprawl on the north shore. Selected species, like the paddlefish and alligator snapping turtle, would benefit from reduced harvesting. The lake could change considerably without such conservation planning. As of 2007, a few examples of future change included more cypress swamps converting to anthropogenic marsh or open water, Chinese tallow displacing native forests, and, with a warming climate, mangrove trees replacing brackish marsh. Hence, the ecosystems of the lake now, and in the future, depend very much upon some basic decisions about human activities in the vicinity of the lake, and, even more so, human activity upstream along the Mississippi River.
As of 2006, the population in the region was over 1.5 million. There have been many problems with the conservation management of forests and wetlands. As of 1995, the United States Geological Survey was monitoring the environmental effects of shoreline erosion, loss of wetlands, pollution from urban areas and agriculture, saltwater intrusion from artificial waterways, dredging, basin subsidence and faulting, storms and sea level rise, and freshwater diversion from the Mississippi and other rivers. With proper management of this lake and its wetlands, there is potential to increase the productivity of wetlands, and to maintain biological diversity to support an ecotourism industry that will diversify the economy.
Northshore
The area north of Lake Pontchartrain is known as the North Shore or the Northshore. It includes the cities of Mandeville, Covington, Abita Springs, Madisonville, Pearl River, Lacombe, and Slidell in St. Tammany Parish; Ponchatoula, Hammond, Amite, and Kentwood in Tangipahoa Parish; and Bogalusa and Franklinton in Washington Parish.These three Northshore parishes are the eastern Florida Parishes. The landscape here is mostly uplands that were once dominated by long leaf pine savannas and interrupted by occasional large rivers. The savannas were maintained by regular fires caused by lightning; they produced the distinctive fauna and flora of this region.
Lake Pontchartrain forms the northern boundary of the city of New Orleans, which is coterminous with Orleans Parish, and the northern boundary of its two largest suburbs, Metairie and Kenner; as well as forming the northern boundaries of Jefferson Parish and Saint Charles Parish, and much of the northern and eastern boundaries of Saint John the Baptist Parish. These regions are often referred to as the South Shore, or Southshore.
New Orleans
New Orleans was established at a Native American portage between the Mississippi River and Lake Pontchartrain. The lake provides numerous recreational activities for people in New Orleans and is also home to the Southern Yacht Club. In the 1920s, the Industrial Canal in the eastern part of the city opened, providing a direct navigable water connection, with locks, between the Mississippi River and the lake. In the same decade, a project dredging new land from the lake shore behind a new concrete floodwall began; this would result in an expansion of the city into the former swamp between Metairie/Gentilly Ridges and the lakefront. The Lake Pontchartrain Causeway was constructed in the 1950s and 1960s, connecting New Orleans with Mandeville, and bisecting the lake in a north-northeast line.Hurricanes
During hurricanes, a storm surge can build up in Lake Pontchartrain. Wind pushes water into the lake from the Gulf of Mexico as a hurricane approaches from the south, and from there it can spill into New Orleans.A hurricane in 1947 flooded much of Metairie, much of which is slightly below sea level due to land subsidence after marshland was drained. After the storm, hurricane-protection levees were built along Lake Pontchartrain's south shore to protect New Orleans and nearby communities. A storm surge of from Hurricane Betsy overwhelmed some levees in eastern New Orleans in 1965, while a storm surge funneled in by the Mississippi River–Gulf Outlet Canal and a levee failure flooded most of the Lower 9th Ward. After this the levees encircling the city and outlying parishes were raised to heights of. Due to cost concerns, the levees were built to protect against only a Category 3 hurricane; however, some of the levees initially withstood the Category 5 storm surge of Hurricane Katrina, which only slowed to Category 3 winds within hours of landfall.
Experts using computer modeling at Louisiana State University after Hurricane Katrina have concluded that the levees were never topped but rather faulty design, inadequate construction, or some combination of the two were responsible for the flooding of most of New Orleans. Some canal walls leaked underneath because the wall foundations were not deep enough in peat-subsoil to withstand the pressure of higher water.