State of the Beach/State Reports/LA/Beach Erosion
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The threat of coastal erosion in the LCZ is significant and remains a paramount issue for LDNR/OCRM. The Louisiana coast has approximately 350 miles of sandy shoreline along its barrier islands and gulf beaches and about 30,000 miles of land-water interface along the bays, lakes, canals, and streams (Louisiana Coastal Wetlands Conservation and Restoration Task Force and the Wetlands Conservation and Restoration Authority 1998). When erosion occurs there is a loss of coastal geomorphology. That is geomorphic features such as natural levees, lake rims, land bridges, cheniers, and barrier islands and shorelines are lost or degraded due to the effects of wind and/or wave erosion. Barrier islands play a critical role in protecting coastal wetlands, bays, and estuaries by reducing wave impacts at the margins of the coastal wetlands and serve as important natural buffers during storms (USACE 2004). Barrier islands are very dynamic and naturally degrade over time. Historic land loss rates of barrier islands can average as high as 50 acres per year over several decades. Hurricane events can cause as high as 300 acres of loss per year (USACE 2004).
Subsidence is a major contributor to coastal erosion and land loss in Louisiana. In 2005 NOAA National Geodetic Survey (NOAA/NGS) began a nationwide campaign to readjust the horizontal position and ellipsoidal heights in the National Spatial Reference System (NSRS) using high accuracy global positioning system data. The project is scheduled for completion in 2007. The last general readjustment occurred in 1986. As part of this initiative, NOAA/NGS and the Louisiana Spatial Reference Center at LSU have released updated elevation information for coastal Louisiana. This survey data will be incorporated into the readjustment of the NSRS. The NSRS data will play a crucial role in emergency planning and response during hurricanes and other natural disasters. It can also be used to inform the reconstruction and ongoing development in the LCZ.
The Chenier plain is positioned to the west of the deltaic plain and is characterized by marsh that is segmented by long, narrow coast-parallel sand and shell ridges. In the last several decades, humans have impacted the Chenier ecosystems with such activities as mining and exporting mined materials out of the Chenier Plains, livestock grazing, fence building, road building, and urbanization. Marine forces such as winds, tides, and currents, may be acting in concert with human activities that favor erosional processes, acting to exacerbate subsidence, and ultimately the loss of these higher elevation geomorphic features. Louisiana’s Chenier plains serve as habitat for neo-tropical, trans-gulf migratory birds, many species of fish and shellfish, and a host of other aquatic and terrestrial species. Resource planners and managers do not know the extent to which the coastal use activities detailed above affect the geomorphic integrity of these Chenier ridges and their ability to provide a natural buffer for storm surge, inland flooding, and saltwater intrusion.
Digital Mapping of Levees, Pumps, and Flood Control Features in Coastal Louisiana and Update of the Regulatory Hazards Protocol
Currently, almost all of the communities in the LCZ have some sort of flood protection system. Most of the cities are surrounded by levees and the water levels controlled by pumps. There is no current map, hardcopy or digital, collectively of these flood protection systems. There are major flood protection systems built and maintained by the USACE and under the control of various state levee boards, other large levee systems maintained by the parish (county) governments, smaller systems under control of public drainage agencies, and numerous privately managed large levee and pump systems protecting residences and agricultural operations. All of the information and maps reside with the respective agency or individuals responsible for the systems; there is no central repository.
The U.S. Geological Survey (USGS) has conducted research studies and monitoring in Louisiana for many years. Their website contains a wealth of coastal erosion data. The first of three major studies undertaken in recent years was the Louisiana Barrier Island Erosion Study, a cooperative effort with the Louisiana Geological Survey that spanned 1986 to 1990. A second study, the Louisiana Wetland Loss Study, was done cooperatively with the National Biological Survey (which became the USGS/ Lafayette Wetlands Research Center) and a team of scientists at Louisiana State University (LSU). The third and most recently completed study involved University of New Orleans (UNO) scientists and was on the geologic framework and processes of the Lake Pontchartrain basin. Smaller scale studies and data collection by the USGS and partners are continuing on mapping shoreline and wetland change and investigating subsidence processes responsible for the high rates of relative sea-level rise across the south Louisiana region, and on geologic surveys of offshore sand resources. More recently (June 2011), USGS announced the release of Land area change in coastal Louisiana from 1932 to 2010. Following is an abstract from that report:
- "Coastal Louisiana wetlands make up the seventh largest delta on Earth, contain about 37 percent of the estuarine herbaceous marshes in the conterminous United States, and support the largest commercial fishery in the lower 48 States. These wetlands are in peril because Louisiana currently undergoes about 90 percent of the total coastal wetland loss in the continental United States. Documenting and understanding the occurrence and rates of wetland loss are necessary for effective planning, protection, and restoration activities. The analyses of landscape change presented in this report use historical surveys, aerial data, and satellite data to track landscape changes. Summary data are presented for 1932-2010; trend data are presented for 1985-2010. These later data were calculated separately because of concerns over the comparability of the 1932 and 1956 datasets (which are based on survey and aerial data, respectively) with the later datasets (which are all based on satellite imagery). These analyses show that coastal Louisiana has undergone a net change in land area of about -1,883 square miles (mi2) from 1932 to 2010. This net change in land area amounts to a decrease of about 25 percent of the 1932 land area. Persistent losses account for 95 percent of this land area decrease; the remainder are areas that have converted to water but have not yet exhibited the persistence necessary to be classified as \"loss.\" Trend analyses from 1985 to 2010 show a wetland loss rate of 16.57 mi2 per year. If this loss were to occur at a constant rate, it would equate to Louisiana losing an area the size of one football field per hour. The use of 17 datasets plus the application of consistent change criteria in this study provide opportunities to better understand the timing and causal mechanisms of wetland loss that are critical for forecasting landscape changes in the future."
The USGS site contains an Atlas of Shoreline Changes in Louisiana from 1853 to 1989. There are also Shoreline Change Posters of the Louisiana Barrier Islands: 1885-1996. Here is a link to 100+ USGS-produced land change maps for coastal Louisiana.
The USGS report National Assessment Of Shoreline Change: Part 1, Historical Shoreline Changes And Associated Coastal Land Loss Along The U.S. Gulf Of Mexico (2004) states:
- "The highest rates of laterally continuous shoreline retreat and land loss in the Gulf of Mexico are found in coastal Louisiana. While land loss associated with shoreline change along the Gulf shore and around the margins of large coastal bays is severe, loss of the interior wetlands is also extensive due to submergence and destruction of the Mississippi River delta plain (Penland and others, 1990). Subsidence and coastal erosion are functions of both natural and human induced processes. The natural delta cycle begins with construction of a delta lobe. Eventually that lobe is abandoned as the river system relocates to another area. Following abandonment, the delta lobe subsides as sediments compact and the area becomes submerged because no additional sediment is available to offset the subsidence. Sediment supply to the delta also has been artificially reduced by controlling the Mississippi River and preventing it from flowing into the Atchafalya Basin. Recent studies have also suggested that hydrocarbon production has been partly responsible for accelerated subsidence and wetland loss (Morton and others, 2002).
- About 90% of the Louisiana Gulf shoreline is experiencing erosion, which increased from an average of -8.2 ± 4.4 m/yr in the long-term to an average of -12.0 m/yr in the short term. Short sections of the shoreline are accreting as a result of lateral island migration. The highest rates of Gulf shoreline erosion in Louisiana coincide with subsiding marshes and migrating barrier islands such as the Chandeleur Islands, Caminada-Moreau headland, and the Isles Dernieres. The frequent breaching of the Chandeleur Islands makes shoreline delineation difficult at many locations and prevents calculation of accurate rates of change along some barrier segments. The change from long-term erosion to short-term accretion on the west end of Grand Isle is related to frequent beach nourishment efforts. Elsewhere, beach nourishment along the Caminada headland and the Isles Dernieres, and a rock revetment along East Timbalier Island have not substantially reduced the rates of erosion at those locations."
The U.S. Geological Survey National Wetlands Research Center is developing updated wetland maps with the U.S. Fish and Wildlife Service’s National Wetlands Inventory, a program that maps wetland and aquatic habitats. The information is provided to governments, universities and private companies for coastal restoration research and planning. The National Wetland Inventory mapped wetlands across the country, including Louisiana, in 1978 and again in 1988. The data hasn’t been updated for 21 years until the latest mapping project began in March 2009.
An article published in the The Times-Picayune in November 2010 was Flooding predictions have dramatic implications for Grand Isle. This article referenced a NOAA study. The effects of relative sea level rise, the combination of subsidence and rising water, will be significant by 2050, according to the study, with as many as 79 flooding events lasting a total of 20 days. The article states: "The study found that relative sea level rise, the combination of rising water levels and sinking land beneath the island, equaled 9.24 millimeters a year -- about a third of an inch -- between 2005 and 2009."
While there were four high-water events lasting 53 hours that inundated the benchmark between 2005 and 2009, the study found that between 2046 and 2050, sea level would have risen by 1.2 feet at the marker, resulting in 79 flood events lasting 478 hours, or 20 days. By the five-year period between 2096 and 2100, sea level will rise by 2.7 feet, which would cause the number of events to skyrocket to 1,241 and to last as long as 22,229 hours, or over half of the 5-year period. A GIS database with the location of levees and pump stations including basic and pertinent information about each of those features does not exist and is needed by many agencies of the State of Louisiana to more efficiently and effectively perform their mandates in the LCZ. Additionally, for those critical applications of protection of life and property, specialized user interfaces, queries, and displays are needed that provide for use of the application without a great deal of training or knowledge of the GIS software. The goal of this project is to complete a GIS dataset of all levees and pump stations in the LCZ, and to develop tools that fulfill aspects of emergency response and planning as described in this proposal, as well as to design the project so that it is flexible enough to be used as a basis for future projects that refine and/or add to the data and utility of the data and tools associated with this project. These data and tools will be used for emergency response and planning; flood protection and drainage projects planning; coastal restoration project analysis and design; and for coastal use regulatory permit application review and determinations.
The DNR website has links to some coastal erosion reports including The Economic Impact of Coastal Erosion in Louisiana on State, Regional, and National Economies.
Two publications (fact sheets) available from the US Geological Survey are Louisiana's Barrier Islands: A Vanishing Resource and Louisiana Coastal Wetlands: A Resource At Risk.
From Hurricanes Katrina and Rita alone, the United States Geological Survey (USGS) reported in a release from July 2007 that the coastal water areas increased by 217 square miles. The USGS also reported that this increase in coastal water areas and associated loss of coastal lands is directly caused by the removal of wetlands. At the time of the report, the USGS could not verify if the land losses would be permanent, but as time progressed, these land losses increased into what they are today.
LSU Professor Robert Twilley estimates that approximately 24 square miles of wetlands are lost per year. This figure does not include the loss rates associated with Katrina and Rita. This land loss has led to a resolution that was recently passed by the Louisiana legislature to redefine the state's coastline. This comes 30 years after the legislature passed a law that first defined the location and mapping of Louisiana's coastline throughout the southern part of the state. The new resolution under the preceding coastal zone law will set the Coastal Protection and Restoration Authority to conduct a "science-based study of the adequacy of the current inland boundary of the coastal zone of Louisiana to meet the state's current and future needs to manage, protect, and restore its coastal resources." This study will define the Louisiana coastline and evaluate the exact land loss among southern parishes. Moreover, this new coastline has the potential to change the map of Louisiana and bring more parishes into the coastal zone. Once a parish is legally located within the coastal zone, it will be able to protect its land and have more power over what happens to the land as a result of government actions. However, a parish will also face the downside of losing commercial and residential interests in the area due to the environmental factors and fears of residing in the zone.
An article published in The Advocate in February 2013 stated:
"Stunning new data not yet publicly released shows Louisiana losing its battle with rising seas much more quickly than even the most pessimistic studies have predicted to date. While state officials continue to argue over restoration projects to save the state’s sinking, crumbling coast, top researchers at the National Oceanic and Atmospheric Administration have concluded that Louisiana is in line for the highest rate of sea-level rise “on the planet.” Indeed, the water is rising so fast that some coastal restoration projects could be obsolete before they are completed, the officials said. NOAA’s Tim Osborne, an 18-year veteran of Louisiana coastal surveys, and Steve Gill, senior scientist at the agency’s Center for Operational Oceanographic Products and Services, spelled out the grim reality. When new data on the rate of coastal subsidence is married with updated projections of sea-level rise, the southeast corner of Louisiana looks likely to be under at least 4.3 feet of Gulf water by the end of the century."
The Heinz Center's Evaluation of Erosion Hazards, conducted for the Federal Emergency Management Agency (FEMA), studied the causes of coastal erosion hazards and proposed a variety of national and regional responses. The study, published in April 2000, concentrates on the economic impacts of erosion response policies as well as the cost of erosion itself to homeowners, businesses, and governmental entities.
A NOAA website that has graphs of sea level data for many coastal locations around the country over the last 40 to 50 years and projections into the future is Sea Levels Online.
NOAA Shoreline Website is a comprehensive guide to national shoreline data and terms and is the first site to allow vector shoreline data from NOAA and other federal agencies to be conveniently accessed and compared in one place. Supporting context is also included via frequently asked questions, common uses of shoreline data, shoreline terms, and references. Many NOAA branches and offices have a stake in developing shoreline data, but this is the first-ever NOAA Website to provide access to all NOAA shorelines, plus data from other federal agencies. The site is a culmination of efforts of NOAA and several offices within NOS (including NOAA’s Coastal Services Center, National Geodetic Survey, Office of Coast Survey, Special Projects Office, and Office of Ocean and Coastal Resource Management) and other federal agencies to provide coastal resource managers with accurate and useful shoreline data.
A related site launched in 2008 is NOAA Coastal Services Center's Digital Coast, which can be used to address timely coastal issues, including land use, coastal conservation, hazards, marine spatial planning, and climate change. One of the goals behind the creation of the Digital Coast was to unify groups that might not otherwise work together. This partnership network is building not only a website, but also a strong collaboration of coastal professionals intent on addressing coastal resource management needs. Website content is provided by numerous organizations, but all must meet the site’s quality and applicability standards. More recently, NOAA Coastal Services Center has developed a Sea Level Rise and Coastal Flooding Impacts Viewer as part of its Digital Coast website. Being able to visualize potential impacts from sea level rise is a powerful teaching and planning tool, and the Sea Level Rise Viewer brings this capability to coastal communities. A slider bar is used to show how various levels of sea level rise will impact coastal communities. Completed areas include Mississippi, Alabama, Texas, Florida, and Georgia, with additional coastal counties to be added in the near future. Visuals and the accompanying data and information cover sea level rise inundation, uncertainty, flood frequency, marsh impacts, and socioeconomics.
Erosion Contact Info
Geologist - DCL
Hazard Avoidance Policies/Erosion Response
See the Erosion Response section.
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