Section 3.2: Ridge Restoration, Dredging, and Structural Breakwaters

    In addition to the sediment diversion projects, there are also some smaller-scale efforts to transport sediments into eroding coastal wetlands in order to augment eroding ridges, which were formed by distributaries of the Mississippi River in the past. Ridge restoration projects work by moving sediment onto deteriorating ridge surfaces. Restored ridges then attract the growth of wetland vegetation, which is capable of holding sediments in place and resisting erosion.
    Another variant of ridge restoration involves the dredging of locally deposited sediment to restore key ridge features on the landscape. This approach is not as effective in the long term as ridge creation involving the piping in of sediment from the Mississippi River channel. However, it is a relatively small-scale and cheap approach to disrupting the erosive forces acting on Gulf Coast wetlands.
    One ridge restoration strategy involves the pumping of sediment from the channel of the Mississippi River onto ridge surfaces via pipelines. An example of this strategy is the Long Distance Sediment Pipeline, which is already operating in Plaquemines Parish. This pipeline is designed to transport sediment that is dredged from the Mississippi River channel to support eroding wetland landscapes in the Barataria Basin. While relatively modest in its scope in comparison with the Barataria sediment diversions, the Long Distance Sediment Pipeline is innovative in making use of sediments from the Mississippi River to reinforce particularly at-risk wetland landscape features in the Barataria Basin. Still, it can be a relatively inexpensive measure that can stabilize wetland landscapes and make them more resistant to erosive forces as longer-term solutions are implemented.
    Another example of this kind of ridge restoration can be seen at Bayou Grand Liard in Plaquemines Parish. This project, which was completed in 2015, dredged sediment from borrow areas along a preexisting sediment ridge, which was the remnant of an eroded distributary of the Mississippi River. Then a sediment slurry was added behind the restored ridge to reinforce the land surface and encourage the growth of vegetation communities. In addition, this project involves the planting of trees along the ridge to further stabilize the land surface.
    The restoration of freshwater coastal wetlands can be an effective method of slowing coastal erosion. As I discussed in Part 1, coastal wetland vegetation communities are key features in resisting the forces of erosion and thus preventing land loss. There are innumerable coastal wetland restoration projects underway around Southeast Louisiana, some of which involve ridge restoration and many of which do not. Given the connection between wetland vegetation and land-scape stability, the restoration of freshwater wetlands along the coast is rightly a priority for Louisiana.
    Finally, there are a number of engineering strategies for slowing coastal erosion that involve the installation of human-made hardware. One version of this strategy is the installation of oyster reefs, which involves placing structures that encourage the growth of oyster beds along at-risk land surface features. Oyster beds are effective anchors for sediments and they resist erosion very effectively (otherwise the poor oysters would be washed out to sea). Thus, this strategy leverages the activities of naturally occurring coastal organisms and it has the added benefit of producing oysters.
    Other human-made structures include breakwaters placed near the shore, which disrupt waves and reduces the force of their impact on the shoreline. Similarly, there is the placement of riprap along eroding land surface features. Riprap refers to linings made from fragments of stone that are placed on top of at-risk sediments. Waves impact the stone riprap lining, which shields the sediment underneath from the force of the impact. Other forms of erosion prevention lining can be made from concrete, plastic, and even natural vegetation. Engineering solutions like breakwaters and riprapping are cheap and can be effective, at least in the short term.

    Ridge restoration, dredging, and riprapping are often favored by opponents of the large-scale sediment diversion projects. The logic behind this belief is that these smaller-scale projects do not have the same kinds of deleterious consequences for saltwater ecosystems, since they do not involve the introduction of freshwater. Instead, they involve the reinforcement of existing landscape structures, which is less expensive and more effective at near-term time scales.
    These kinds of opinions are valid and such approaches to coastal restoration have great value in many situations. Yet, it is worth remembering that they do not address the greater geological source of Southeast Louisiana’s land loss problems: without a sediment supply, coastlines will erode, especially given the current conditions of sea level rise and geological subsidence. In my opinion, at least, the long-term prospects for Louisiana’s coast depend on maintaining geologically dynamic and ecologically healthy estuarine landscapes. While they can be very useful in many situations, such smaller-scale engineering solutions do little to address our larger geological and ecological problems.