Case in Point: Bayou LaBranche

To understand the role monitoring plays, consider the example of an early CWPPRA project by the U.S. Army Corps of Engineers: Bayou LaBranche Wetland Creation, constructed in 1994 in St. Charles Parish. This project succeeded at creating 380 acres of wetlands using approximately 2.7 million cubic yards of sediment dredged from Lake Pontchartrain.

The project’s monitoring plan called for tracking several key indicators, such as elevation and the ratio of land to water. Other variables included the percent of organic matter in the soil, vegetation composition and abundance, water level and salinity. This was to provide a more comprehensive understanding of the interactions and processes influencing marsh development in the project area.

Monitoring documented the dredge material’s average elevation as it settled and compacted, from 1.6 feet in 1994 to 0.7 feet NAVD 88 (North American Vertical Datum of 1988) by 2002. Coinciding with the drop in elevation was a shift in vegetation from woody species that thrive in uplands to herbaceous species better suited to wetlands. Also, there was a shift in the land-to-water ratio from 18:82 immediately prior to construction to a more desirable 87:13 ratio eight years later. Knowing the rate of settling and change in vegetation species helped set construction targets for future dredge material projects.

Allen Ensminger, a consultant for the LaBranche property owner, notes, “The Bayou LaBranche project is now in its 10th year, and the results are right on target with what we anticipated. In fact, we have another 2-3,000 acres of water adjacent to this site that we think would be suitable for another dredge and fill project.”

TOP IMAGE: Data from aerial photography are analyzed to assess progress toward specific project goals. This graphic, based on data collected seven years after marsh creation in Bayou LaBranche on the south shore of Lake Ponchartrain, quantifies the change in the ratio of land to water.

BOTTOM IMAGES: Aerial photography plays a critical role in the monitoring process. These before and after aerial photographs of Bayou LaBranche show the growth in marsh from Nov. 7, 1993 to Nov. 17, 1997.

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