• The Mississippi: A Visual Biography by Quinta Scott

    "Great book and great blog - thanks for the first book I have seen that addresses the contemporary river, headwaters to gulf." Dan McGuiness, Audubon, St. Paul, Minnesota

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“The weeds and grass in this portion of the bayou point to the fact that, if but let alone, its entire closure is but a matter of a short time. It was noted that during a falling tide the current was very slight, and this slight current flowed towards Bayou Barataria instead of, as would naturally be supposed, flowing toward Barataria Bay, the natural outlet of the bayou. This abnormal condition of affairs must be caused by the obstructed condition of the bayou below the point where the examination terminated.”–H.R. Douglas, Assistant Army Engineer, 1881

 

 

Bayou Dupont at Cheniere Traverse Bayou: A narrow bayou on the verge of silting in in Douglas's time is now wide and on the verge of becoming ever wider without restoration

Bayou Dupont at Cheniere Traverse Bayou: A narrow bayou on the verge of silting in in Douglas's time is now wide and on the verge of becoming ever wider without restoration

Historically, a quartet of narrow bayous–Perot, Barataria, Dupont, and Villars–meandered through a landmass, a landbridge that ranged southwest to northeast from the Bayou Lafourche ridge on the west to the Mississippi ridge on the east in the central Barataria basin between Lake Salvador and Little Lake. The landmass served as a barrier to saltwater intrusion from the lower basin–dominated by saline marshes, to the upper basin–dominated by fresh marshes and swamps. Little saltwater made its way into the narrow bayous. And, the landbridge thwarted tidal exchange.

 

 

Bayou Dupont

Bayou Dupont

Wave erosion, tidal energy, subsidence, and the rise in sea level eroded the bayous and their interior marshes. The elimination of overbank flooding from the Mississippi and the closure of Bayou Lafourche shifted the basin from a river-dominated system to a tidal-dominated system. The dredging of the various waterways: the Intracoastal, the Barataria, the Harvey Cutoff, and the oilfield access channels allowed in saltwater. Salty tides washed away the organic soils, peat and root mats, that composed the landbridge. Summer storms blowing in from the south could raise water levels several feet above the marshes. Winter winds from the north could push the water out and expose mudflats to erosion.

 

In 1880 H.R. Douglas found a narrow stream, filling with vegetation and flowing both north and south. At the beginning of the twentieth century it flowed along the southern rim of the impounded Pen, a large area of open water. By end of the twentieth century it headed at the southeast corner of the Pen and still flowed north and south, depending on the direction of the tide. The marshes it flowed through were breaking up. And, the State of Louisiana initiated two innovative programs to restore Bayou Dupont’s interior marshes.

In 1998 the Louisiana Department of Natural Resources received funding for its dedicated dredging program. The agency dispatched small hydraulic dredges to sites in Lake Salvador and along Bayou Dupont to test the possibility of moving sediment from the beds on inland waterways, depositing it at selected sites, and creating new marshes or restoring old ones. Five years later the EPA and the DNR received approval to design a pipeline to deliver sediment dredged from the Mississippi to 400 acres of deteriorating marshes between Cheniere Traverse Bayou on the north and Bayou Dupont on the south.

 

The Pen, Bayou Cheniere Traverse, and Bayou Dupont

The Pen, Bayou Cheniere Traverse, and Bayou Dupont

In May 2000 the dredge Crownpoint sucked up sediment from a borrow pits 200 feet wide, 1,900 feet long, and fifty feet from the shoreline at the head of Bayou Dupont at The Pen. It discharged its dredge into shallow open water behind containment dikes at site one to the south, building up marsh to a level six inches above the existing marsh elevation. Once deposited to the proper elevation, sheet flow carried a thin layer of sediment and nutrients through the existing marsh grass at the perimeter of the site. In June the Crownpoint moved on to site two and to site three in August. In all the Crownpoint moved 448,725 cubic yards of sediment to the three sites, creating 160 acres of new marsh and benefiting 24 acres of existing marsh at a cost of $1,080,016.50.

 

When the DNR completed the work at both Lake Salvador and Bayou Dupont, it came up with a series of recommendations for obtaining the most from dedicated dredging: Select project areas that require the least amount of containment dike. Choose areas of broken marsh and open water that are no more than two feet deep, are no more than thirty acres big, and are surrounded by stable existing marsh. Choose areas that are accessible by dredges with a five-foot draft. The pipeline need be no more than twelve inches in diameter. Each bid package should cover everything–permits, landrights, design, and engineering–for one year.

The Mississippi River Sediment Delivery System is the dedicated dredging project writ large. The process is the same, borrow sediment from a sediment trap in the streambed of the Mississippi and deliver it by pipeline to marshes at the western edge of the Mississipi ridge and between Cheniere Traverse Bayou and Bayou Dupont. As the sediment spreads over the project area, natural ridges would contain it. In a few places low containment levees may have to be built. By dredging the river instead of the two small bayous, the project would avoid disrupting the adjacent marsh. And, the source, the Mississippi, would be renewable. The Mississippi may have lost sediment in its water column in the last century, but there was plenty there for this project and others like it, and more coming, which will fill the trap.  The DNR and the EPA completed design of the project in March 2007, and was expected to start construction in November 2008.

 On April 16, 209, Louisiana’s Gov. Bobby Jindal announced the beginning of the project. It’s cost is $28.3 million to build 500 acres of new marsh. The pipeline will deliver 2.3 million cubic yards of sediment from the Mississippi to Bayou Dupont. That done, wetland managers, and possibly volunteers, will plant native vegetation to hold the mud in place. 

Once this project is completed, the pipeline will be left in place to be used for other similar projects. 

 

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