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Coastal and Marine Geology Program > The Lake Pontchartrain Basin: Louisiana's Troubled Urban Estuary

The Lake Pontchartrain Basin: Louisiana's Troubled Urban Estuary

USGS Fact Sheet

S. Jeffress Williams
S. Jeffress Williams
"Scientific studies recently begun by the U.S. Geological Survey suggest that several key natural processes and human-induced environmental factors are directly affecting the health of the Lake Pontchartrain Basin, one of America's largest estuaries. An increased knowledge of the critical geologic and estuarine processes affecting the Basin is essential for its management, improving environmental conditions, and mitigating future problems in the region. Such baseline information is of immediate value to planners and decision makers involved in the task of reversing the Basin's environmental degradation and restoring its water and habitat qualities."

- S. Jeffress Williams, U.S. Geological Survey

Development and urbanization in the New Orleans region over the past 300 years is projected to continue and places stress on the Lake Pontchartrain Basin environment.

Earliest human habitation began at least 3,500 years ago, but concentrated rapid growth in the area between Lake Pontchartrain and the Mississippi River began nearly 300 years ago with influx of European settlers, resulting in a population of over 1.5 million people. Today, the Basin faces many challenges, all of which are affected by the geologic character of this dynamic coastal region. The more significant of the environmental issues include erosion of Lake Pontchartrain shores, wetland losses, water and sediment pollution from urban outfalls and agricultural runoff, saltwater intrusion from navigation waterways, possible effects of past commercial shell dredging, impacts of basin subsidence and faulting, effects of storms and sea-level rise, and potential impacts on circulation patterns of future freshwater diversions from the Mississippi River. Continued losses of wetland and estuarine habitats, water and sediment pollution, and diminished fish and wildlife resources are some of the results if historical trends continue.

Map showing the Lake Pontchartrain Basin area.
Map showing the Lake Pontchartrain Basin area. The combination of natural processes and mankind's impacts are threatening the Basin. [larger version]

The U.S. Geological Survey (USGS) is uniquely qualified to conduct research needed to increase scientific knowledge of the Lake Pontchartrain Basin's character.

The long-term investigation extends previously completed and ongoing USGS geologic studies in the Mississippi River deltaic plain of southern Louisiana on topics such as barrier island erosion, regional-scale wetlands losses and deterioration, the long-term effects of marsh management, and water quality. Investigations of the Lake Pontchartrain Basin complement studies by several Federal and State agencies with which USGS scientists collaborate. An evaluation conducted in preparation for this study determined necessary baseline data, information, and geo-science studies required to better understand the character of the Basin and the geologic processes affecting the region. The evaluation suggested a well-defined set of geologic issues that could be addressed jointly with other organizations having expertise that complements geoscience expertise available in the USGS.

USGS scientists are increasing their knowledge of the geologic sedimentary framework within which processes are taking place.

Map showing shorelines types (swamp, marsh, beach, and armored) in the Pontchartrain basin.
Shorelines in the Pontchartrain basin exhibit wide variability. [larger version]
A mix of regional and site-specific studies provide data not presently available on shallow sedimentary structures and the composition and variability of lakebed sediments. These studies are combined with a detailed analysis of lakebed bathymetric changes. Results will yield a regional sediment budget with sediment sinks and sources identified which are critical for deciphering recent geological and historical development of the Basin and the important natural and human-induced processes involved in the Basin's evolution. With this information, USGS scientists can quantify the natural variability of geologic processes and differentiate natural processes from effects of human activity. Such information is critical for restoring and protecting the Pontchartrain estuary.

Shorelines, wetlands, and the lakebed in the Lake Pontchartrain Basin have been in a state of dynamic flux since the Basin formed several thousand years ago.

Shoreline erosion and loss of wetlands are critical issues.
Shoreline erosion and loss of wetlands are critical issues. [larger version]
Shorelines have shifted position and many wetland areas have suffered loss and deterioration in response to processes such as storms, regional subsidence, rise in sea level, varying sediment input from the Mississippi River and smaller rivers, and more recently, the effects of human activity and development. USGS scientists are preparing a suite of maps at useful scales to accurately and quantitatively delineate environmental changes that have occurred. These maps are based on information from the earliest data available up to the latest high-resolution satellite images. In addition, thematic map sets will depict the general Basin geology, sediment types, directions and volumes of water circulation and sediment transport, wetland distribution, and Basin resources. Information in map form and computer databases will provide the basic framework to planners and environmental engineers.

Perceptions are widespread and common among the general public that Lake Pontchartrain Basin is both a source and a sink for contaminated sediments.

Scientific baseline data are being systematically collected to document Basin-wide sources and conditions of contamination. These data allow USGS scientists to differentiate natural background chemicals in the sediments from chemicals derived from human activity. Many known contaminants are associated with fine-grained sediments, such as mud and silt, particularly the organic-rich sediments comprising much of the lakebed. Muddy sediments are stabilized by sea grasses growing on parts of the lake floor, but muddy sediments in bare areas of the shallow Basin are frequently resuspended by waves, currents, and flooding. Resuspension may lead to redistribution of contaminants and generally increases turbidity. Recent flooding during May 1995 in the New Orleans area illustrates how contaminants can potentially enter the basin and be redistributed. This study provides systematic collection of lakebed sediment samples, analyses for sediment composition and geochemical characteristics, and inclusion in a computer database. In addition, instruments are deployed to monitor waves, currents, and turbidity. This information is extrapolated across the Basin using state-of-the-art high-resolution satellite imagery and 3-dimensional computer models of Basin circulation.

USGS researchers are determining wave energy distribution and circulation patterns at varying time scales.

Studies of these kinds are necessary to understand the transport and dispersal of turbid waters and sediments in the Lake Pontchartrain Basin. Circulation, controlled largely by inflow and outflow of fresh and tidal water and by atmospheric conditions, is the primary process for moving, dispersing, and concentrating fine-grained sediments and associated contaminants. Currently, little information is available on wave energy and movement of sediments and water masses in the Basin. Early physical and computer models have given preliminary results, but predictions of future conditions influenced by a variety of new engineered structures still have a high degree of uncertainty. Circulation models will be used to predict changes in distribution of turbid waters, rates of flushing in the Basin, and changes in salinity gradients resulting from engineering projects like the Bonnet Carre diversion.

USGS will distribute results of investigations and scientific analyses to a wide variety of user groups.

Interim and final results of field investigations and scientific analyses will be distributed to engineers, coastal zone managers and planners in Federal, State, and local government and universities, and to scientific colleagues and to the general public. A variety of information transfer methods, used successfully in other coastal studies, will be employed in this study. Communicating information and results to the citizens of Louisiana through educational materials is an important objective. Partnerships with local and environmental-interest groups will foster the kind of public education needed to insure the long-term sustainable use of Pontchartrain's resources.

Contact Information
S. Jeffress Williams
U.S. Geological Survey
384 Woods Hole Road
Woods Hole, MA 02543
Phone: (508) 457-2383
Fax: (508) 457-2310

Related Research Projects:

Geologic Framework and Processes of the Lake Pontchartrain Basin
USGS Coastal & Marine Geology Program

Subsidence and Sea-Level Rise in Southeastern Louisiana: Implications for Coastal Management and Restoration
USGS Coastal & Marine Geology Program

Subsidence and Fault Activation Related to Fluid Energy Production, Gulf Coast Basin Project
USGS Coastal & Marine Geology Program

Related Publications:

Environmental Atlas of the Lake Pontchartrain Basins - USGS Open File Report 02-206
USGS Coastal & Marine Geology Program

Related Links:

Lake Pontchartrain Basin Foundation
non-profit organization

University of New Orleans
University of New Orleans

Coastal and Marine Geology Program > The Lake Pontchartrain Basin: Louisiana's Troubled Urban Estuary

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