Lake Pontchartrain

Lake Pontchartrain
Landsat image
Map
Location Louisiana
Lake type Estuary, saline
Basin countries United States
Max. length 40 mi (64 km)
Max. width 24 mi (39 km)
Surface area 630 sq mi (1630 km²)
Average depth 12-14 feet
Settlements New Orleans, Metairie, Kenner, Mandeville, Slidell, Madisonville.o
Lake Pontchartrain's north shore at Fontainebleau State Park near Mandeville, Louisiana in 2004

Lake Pontchartrain (pronounced /ˈpɒntʃətreɪn/; French: Lac Pontchartrain, French: [lak pɔ̃ʃaʁtʁɛ̃]  ( listen)) is a brackish estuary located in southeastern Louisiana. It is the second-largest saltwater lake in the United States, after the Great Salt Lake in Utah, and the largest lake in Louisiana. It covers an area of 630 square miles (1630 square km) with an average depth of 12 to 14 feet (about 4 meters). Some shipping channels are kept deeper through dredging. It is roughly oval in shape, about 40 miles (64 km) wide and 24 miles (39 km) from south to north. In descending order of area, the lake is located in parts of St. Tammany, Orleans, Jefferson, St. John the Baptist, St. Charles, and Tangipahoa parishes.

Contents

Namesake

Lake Pontchartrain is named for Louis Phélypeaux, comte de Pontchartrain, the French Minister of the Marine, Chancellor of France and Controller-General of Finances during the reign of France's "Sun King," Louis XIV, for whom Louisiana is named.[1]

Description

Lake Pontchartrain is not a true lake but an estuary connected to the Gulf of Mexico via the Rigolets strait (known locally as "the Rigolets") 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.

Salinity 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 fresh water 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 created 2,600 to 4,000 years ago as the evolving Mississippi River Delta formed its southern and eastern shorelines with alluvial deposits.[2] Its Native American name was Okwata ("Wide Water"). In 1699, French explorer Pierre Le Moyne d'Iberville renamed it Pontchartrain after Louis Phélypeaux, comte de Pontchartrain.

Human habitation of the region began at least 3,500 years ago, but increased rapidly with the arrival of Europeans about 300 years ago. The current population is over 1.5 million. The United States Geological Survey is 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.[3]

Northshore

North of Lake Pontchartrain is an area called the North Shore or Northshore or the Northlake area. It is composed of cities such as Mandeville, Covington, Abita Springs, Madisonville, Lacombe, Slidell in Saint Tammany Parish; Ponchatoula, Hammond, and Amite in Tangipahoa Parish; and Franklinton and Bogalusa in Washington Parish. These Northshore parishes form the eastern Florida Parishes. They constitute most of the primary service area for Southeastern Louisiana University in Hammond and are coterminous with ZIP codes beginning with "704" (Southeastern's five digit ZIP code, for example, is 70402).

The Southshore areas, instead of being designated by that name, are more likely to be referred to as either "Eastbank" or "Westbank" depending on their position with respect to the general direction of flow of the Mississippi River.[4] Lake Ponchartrain forms the northern boundary of the city of New Orleans, which is coterminous with Orleans Parish, and its two largest suburbs Metairie and Kenner as well as the northern boundary of Jefferson Parish and Saint Charles Parish and much of the northern and eastern boundaries of Saint John the Baptist Parish.

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 (by way of Metairie) with Mandeville and bisecting the lake in a north-northeast line. At 24 miles (39 km), the Causeway is the longest bridge over a body of water in the world.

Hurricanes

Lake Pontchartrain at New Orleans during Hurricane Georges in 1998; lakefront camps outside of the protection levee suffered severe damage.

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 September, 1947 flooded much of Metairie, Louisiana, 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 10 feet (3 m) from Hurricane Betsy overwhelmed some levees in Eastern New Orleans in 1965 (while 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 14 to 23 feet (4–7 m). 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 (August 2005), which only slowed to Category 3 winds within hours of landfall (due to a last-minute eyewall replacement cycle).

Experts using computer modeling at Louisiana State University subsequent to 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.[5]

Funding

Congress failed to fully fund an upgrade requested during the 1990s by the Army Corps of Engineers, and funding was cut in 2003-04 despite a 2001 study by the Federal Emergency Management Agency warning that a hurricane in New Orleans was one of the country’s three most likely disasters.[6] Raising and reinforcing the levees to resist a Category 5 hurricane might take 25 years to complete.[7] Some estimates place the cost at $25 billion.

Hurricane Katrina

Windspeed of Hurricane Katrina 7 a.m., showing hurricane-force winds (yellow/brown/red: 75-92 mph) hitting the northeast/south shores of Lake Pontchartrain (1 hour after landfall) on 29-Aug-2005.
Windspeed of Hurricane Katrina 10 a.m., showing hurricane-force winds (yellow/brown) still hitting the north/southeast shores of Lake Pontchartrain (4 hours after landfall)

When Hurricane Katrina reached Category 5 in 2005, some experts predicted that the levee system might fail completely if the storm passed close to the city. Although Katrina weakened to a Category 3 before making landfall on August 29 (with only Category 1-2 strength winds in New Orleans on the weaker side of the eye of the hurricane), the outlying New Orleans East along south Lake Pontchartrain was in the eyewall with winds, preceding the eye, nearly as strong as Bay St. Louis, MS. Canals near Chalmette began leaking at 8 am, and some levees/canals, designed to withstand Category 3 storms, suffered multiple breaks the following day (see Effect of Hurricane Katrina on New Orleans), flooding 80% of the city.

The walls of the Industrial Canal were breached by storm surge via the Mississippi River Gulf Outlet, while the 17th Street Canal and London Avenue Canal experienced catastrophic breaches, even though water levels never topped their flood walls. Louisiana State University experts presented evidence that some of these structures might have had design flaws or faulty construction.[8]

There are indications that the soft earth and peat underlying canal walls may have given way. In the weeks before Katrina, tests of salinity in seepage pools near canals showed them to be lake water, not fresh water from broken mains. The 5.5 mile (9 km) long I-10 Twin Span Bridge heading northeast between New Orleans and Slidell was destroyed. The shorter Fort Pike Bridge crossing the outlet to Lake Borgne remained intact.

Much of the northern sector of the suburban areas of Metairie and Kenner was flooded with up to 2–3 feet of water. In this area, flooding was not the result of levee overtopping, but was due to a decision by the governmental administration of Jefferson Parish to abandon the levee-aligned drainage pumping stations.[9] This resulted in the reverse flow of lake water through the pumping stations into drainage canals which subsequently overflowed, causing extensive flooding of the area between I-10 and the lakefront. When the pump operators were returned to their stations, water was drained out of Metairie and Kenner in less than a day, in some cases, only a few hours.

On September 5, 2005, the Army Corps of Engineers started to fix levee breaches by dropping huge sandbags from Chinook helicopters. The London Avenue Canal and Industrial Canal were blocked at the lake as permanent repairs started. On September 6, the Corps began pumping flood water back into the lake after seven days in the streets of New Orleans. Because it was fouled with dead animals, sewage, heavy metals, petrochemicals, and other dangerous substances, the Army Corps worked with the U.S. Environmental Protection Agency‎ and Louisiana Department of Environmental Quality (LDEQ) to avoid major contamination and eutrophication of the lake.[10]

Aerial photography suggests that 25 billion gallons (95 bn liters) of water covered New Orleans as of September 2, which equals about 2% of Lake Pontchartrain's volume. Due to a lack of electricity, the city was unable to treat the water before pumping it into the lake. It is unclear how long the pollution will persist and what its environmental damage to the lake will be, or the hazards from the mold and contaminated mud remaining in the city.

On September 24, 2005, Hurricane Rita did not breach the temporary repairs in the main part of the city, but the repair on the Industrial Canal wall in the lower 9th ward was breached, allowing about 2 feet (0.61 m) of water back into that neighborhood.

Popular culture

Notable deaths

See also

References

  1. ↑ Louisiana Department of Culture, Recreation and Tourism. "Lake Pontchartrain Historical Marker". http://www.stoppingpoints.com/louisiana/Orleans/Lake+Pontchartrain.html. 
  2. ↑ "Environmental Atlas of the Lake Pontchartrain Basin". USGS Coastal and Marine Geology Program. May 14, 2002. http://pubs.usgs.gov/of/2002/of02-206/env-overview/geologic-history.html. Retrieved 2006-06-15. 
  3. ↑ "The Lake Pontchartrain Basin: Louisiana's Troubled Urban Estuary". U.S. Geological Survey. November 3, 1995. http://marine.usgs.gov/fact-sheets/Pontchartrain/. Retrieved 2006-06-15. 
  4. ↑ See, e.g., the article on the Westbank Expressway. In actuality in this realm of the Mississippi River's course, by compass directions the "Westbank" is really the north bank and the "Eastbank" the south bank. Cf. Uptown New Orleans and Downtown New Orleans.
  5. ↑ Grunwall, Michael; Glasser, Susan B. (September 21, 2005). "Experts Say Faulty Levees Caused Much of Flooding". washingtonpost.com. http://www.washingtonpost.com/wp-dyn/content/article/2005/09/20/AR2005092001894_pf.html. Retrieved 2006-06-15. 
  6. ↑ Blumenthal, Sidney (August 31, 2005). ""No one can say they didn't see it coming"". Salon.com. http://www.salon.com/opinion/blumenthal/2005/08/31/disaster_preparation/. Retrieved 2006-06-15. 
  7. ↑ Handwerk, Brian (September 2, 2005). "New Orleans Levees Not Built for Worst Case Events". National Geographic News. http://news.nationalgeographic.com/news/2005/09/0902_050902_katrina_levees.html. 
  8. ↑ Grunwald, Michael; Glasser, Susan B. (September 21, 2005). "Experts Say Faulty Levees Caused Much of Flooding". washintonpost.com. http://www.washingtonpost.com/wp-dyn/content/article/2005/09/20/AR2005092001894_pf.html. Retrieved 2006-06-15. 
  9. ↑ Broussard says he didn't send pump operators away - Kenner Bulletin - NOLA.com.
  10. ↑ USACE (September 2005). "Quick, coordinated efforts reduce environmental impact on Lake Pontchartrain". usace.army.mil. http://www.hq.usace.army.mil/cepa/katrina/environment.html. Retrieved 2007-07-03. (Dead link)
  11. ↑ "Body Discoverd--Two Decade Mystery Begins". Sex-offenders.info. http://www.sex-offenders.info/detail.php?id=30158. Retrieved 27 January 2010. 
  12. ↑ "Patriot Hill is found dead". boston.com. http://www.boston.com/sports/football/patriots/articles/2007/05/29/patriot_hill_is_found_dead/. Retrieved 27 January 2010. 
  13. ↑ "Navy pilot presumed dead after crash in Lake Pontchartrain". cnn.com. http://www.cnn.com/2010/US/01/25/louisiana.pilot.search/index.html?hpt=T2. Retrieved 25 January 2010. 

Further reading

External links