Hydrology of Louisiana’s Wetlands Loss of Wetlands The coastal wetlands are eroding at exceedingly high rates. In the 1970s, when land loss rates were at their peak, 50 square miles of land disappeared each year 3. Since the recognition of the problem in the 1980s, several plans to reduce land loss have been implemented, but none have made a significant change. Currently, an area the size of a football field is lost every 35 minutes 4, amounting to nearly 24 square miles of wetlands each year. Scientists predict it will be only 10 years before the loss becomes irreversible 5. Important Waterways The Mississippi River winds around New Orleans, leading to the Gulf of Mexico. Due to seasonal flooding of the river, barriers called levees were built along the banks to protect homes, farms and businesses. The Mississippi River Gulf Outlet (MRGO) began in 1940 as a vision to expand navigational capabilities and provide a quicker route to the Gulf. The canal was built through the wetlands between 1958 and 1968 by the Army Corps of Engineers. It is 76 miles to the Gulf of Mexico via MRGO and 120 miles by river. Due to erosion, the width of the waterway has expanded from 600 feet to 2000 feet in some places. The original goal was to stimulate economic growth, but current usage of the canal is minimal and maintenance costs can exceed $20 million a year 6. Lake Pontchartrain sits directly north of the city. When development extended toward the lake in 1800s, the surrounding swampland was filled in and levees were built along its shores. Canals, such as the 17th Street and London Avenue Canals, were constructed as a means of draining rain water from the city into the lake 1. The Atchafalaya Delta lies at the end of the Atchafalaya River, which branches off the Mississippi. Deltas in this region experience land gain rather than loss due to successfully deposited sediment in the surrounding marshes 7. WETLAND LOSS: CAUSESEFFECTS Subsidence Constricting the Mississippi 8 : Levees built along the river to protect homes from floods Jetties erected at the mouth of the river to prevent sandbars from forming that interfere with shipping traffic Lack of firm land 9 : Louisiana is built on silt, instead of firm bedrock The Mississippi River carries sediment that can deposit in the wetlands at the delta. The sediment gets trapped in marshlands and provides a foundation upon which other plants can grow. Levees prevent the river from overflowing and depositing sediment into the interior wetlands. Jetties prevent build up of sand and soil at the mouth of the river, concentrating river flow and diverting sediment into the Gulf of Mexico. The decrease in soil deposition and the compaction of land have ensured that for every square mile of land created, the Gulf tides erode five more. Salt Water Intrusion Dredging canals across the wetlands: 20,000 miles of canals built to serve numerous industries 3 MRGO built to provide quicker, safer route to the Gulf of Mexico – 27,000 acres lost as a result of construction and maintenance 10 The network of waterways, including the MRGO, allows salt water to flow from the Gulf inward. Freshwater habitats cannot survive in the saline environment and vegetation dies off, leaving gaping holes in the marsh. These holes get larger as tides erode their banks and strong winds carry away plants. Holes turn into lagoons and lagoons become lakes. Storms Hurricane Katrina destroyed 118 square miles of marshland in one day 3 Integrity of wetlands further reduced. The greater New Orleans metropolitan area is composed of Orleans, Jefferson, Saint Charles, Saint Bernard and Saint Tammany parishes. It is bordered by Lake Pontchartrain to the north and the Mississippi River to the south. Lake Pontchartrain is a tidal basin about 640 square miles in area and is connected to the Gulf of Mexico 1. Due to its geographical location, New Orleans has been historically prone to flooding by the Mississippi River, but throughout the 20th century both natural and human activity rapidly accelerated the subsidence of the low-lying area. The negative elevation (8.0 feet below sea level in some areas 2 ) increases the city’s vulnerability to hurricane-induced storm surges, waves and rainfall. Fortunately, expansive wetlands stand between one of the nation’s most valuable port cities and the Gulf of Mexico. The wetlands, composed of dense cypress swamp, marshes, natural levee ridges, barrier islands and reefs, provide storm surge protection for New Orleans, with every 3.8 – 4.3 miles reducing storm surge by one foot 3. For 6,000 years the Mississippi River built up these wetlands by depositing nutrient-rich soil across the delta. The unique structure of land and water makes the wetlands an ideal location for countless bionetworks of plants and animals. Louisiana’s fisheries provide one-third of the fish harvested in the continental United States and rely heavily on the diverse collection of fish and shellfish species living in the wetlands. Furthermore, the country’s oil and gas industries are concentrated in the Gulf region. 14,000 miles of pipelines run through the marshlands and receive their added protection 3. In the past 75 years, one third of the wetlands have washed away. The steady disintegration of coastal land endangers its ecosystems, threatens energy facility infrastructure, and greatly reduces the integrity of the area to buffer approaching storms. Figure 3. Atchafalaya Delta Figure 2. Land changes around Mississippi River Delta Figure 4. Silt off the coastSOLUTIONS Learn from nature Within the Atchafalaya Basin, land around the deltas is growing because sediment reaches coastal wetlands 7 (Fig. 3). This directly contrasts with the Mississippi River Delta, around which land is being lost (Figs. 1 and 2). Redirecting fresh water from the Mississippi River, bayous and the Intracoastal Waterway will restore natural sediment delivery and reestablish fresh water habitats 8. Restore the wetlands The habitats created by the fresh water diversions allow sensitive vegetation to flourish and stimulate a cycle of growth. The vegetation traps sediment and provides a stable environment in which plants, animals and other freshwater organisms can thrive. Rebuilding barrier islands and beaches with wide dunes surrounded by shelves of sand and sediment can add storm surge protection and reduce the effects of forceful waves that cause erosion. Figure 1. Louisiana and the Mississippi River Delta References 1. Army Corps of Engineers: History of Lake Pontchartrain and Vicinity Hurricane Protection Project, United States Government Accountability Office, U.S. Geological Survey (USGS). (2008) Coastal Wetlands Planning, Protection and Restoration Act (CWPPRA): A Response to Louisiana’s Land Loss, Louisiana Coastal Wetlands Conservation and Restoration Task Force, Handwerk, B. (9 February 2005). News Archive: Louisiana Coast Threatened by Wetlands Loss. National Geographic. Retrieved April 29, 2008, from 5. Marshall B. (4 March 2007). Last Chance: The fight to save a disappearing coast. Times-Picayune. 6. Army Corps of Engineers: FAQs on MRGO. (16 March 2007). 7. Atchafalaya Basin. Retrieved from 8. Schleifstein, M. (6 March 2007). Laying the Groundwork. Times-Picayune. 9. Subsidence and Sea Level Rise in Louisiana: A Study in Disappearing Land. Retrieved from Brown, M. (5 March 2007). Industry keeps marching through state’s wetlands. Times-Picayune. 11. Images taken from USGS Floton, floating marsh