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Coastal & Marine Geology Program > St. Petersburg Coastal and Marine Science Center > Lake Pontchartrain Basin

Geologic Framework and Processes of the Lake Pontchartrain Basin

Lake Pontchartrain Basin Home
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Geologic Framework
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Wetland Change
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Bonnet-Carré Spillway Event
Water Turbidity
Sea-Surface Temperature
1997 Algal Bloom
Project Contact:
Jack Kindinger

Bonnet Carré Spillway Event

Flood Plan
Floodplan: adapted from USACE. Flow rates shown are measured in cubic feet per second.
During the course of the project, El Niño related flooding in the central United States led to an event that allowed researchers to observe the impact of catastrophic change to the estuarine system of the Pontchartrain Basin, as major flooding of the Mississipi River was diverted through the lake. In response, additional surveys were added to the project to ensure that such a significant event did not go unnoticed.

Lake Pontchartrain is connected to the Mississippi River by the Bonnet-Carré Spillway. The spillway and its flood control structure were designed to divert flood waters from the Mississippi River through the lake, to avoid potential flooding of the New Orleans area.

Under normal conditions, Mississippi River water is vastly different of that from the lake. Additionally, the river water contains abundant contaminants as well as nutrients drained from the continent's interior. The estuarine environment of Lake Pontchartain remains relatively constant, thus changes in water quality have tremendous impact on conditions within the lake. During flood events, lowered salinity and oxygen in the water column and increased turbidity take their toll on the biology of the lake. Subsequent algal bloom events associated with dissolved nutrients in the flood waters further affect the aquatic organisms.

  opening of the spillway
Above: Opening of the spillway March 17, 1997
 
spillway after closure
Above: Spillway lakeside after closure
In March 1997, the Bonnet Carré flood control structure was opened to relieve the worst flooding of the Mississippi River since 1937. Flow gauge measurements upriver in Natchez, Mississippi measured a river crest over 10 feet above flood stage. Flow rates at the time exceeded two million cubic feet a second, enough water to fill the Superdome in New Orleans every second.

stream gauge graph
Natchez, Mississippi Flow Gauge Measurements: click to view a larger version
 
During the diversion, turbidity within Lake Pontchartrain from the flood waters were imaged using the Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA polar-orbiting weather satellites (see below). Water reflectance measured in the visible and near-IR wavelengths are determined with corrections for atmospheric effects, and converted to provisional estimates of suspended sediment concentration (seston) and diffuse attenution coefficient (K). These values have not been validated and are provided for context only. Clouds are masked in gray; land in brown.

The Bonnet Carré Spillway connects the Mississippi River to Lake Pontchartrain and enters the lake in the southwest corner, half-way between Lake Maurepas and New Orleans. The following images illustrate the increase in suspended material in the lake as a result of the diversion of flood waters.

Bonnet-Carré Spillway Event Satellite Images

March 3, 1997

March 6, 1997

March 7, 1997

March 8, 1997

March 9, 1997

March 10, 1997

March 11, 1997

March 18, 1997

March 23, 1997

March 24, 1997

March 26, 1997

March 27, 1997

March 29, 1997

April 2, 1997

April 6, 1997

April 7, 1997

April 9, 1997

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Coastal & Marine Geology Program > St. Petersburg Coastal and Marine Science Center > Lake Pontchartrain Basin


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