mississippi river delta
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The State of Louisiana is leading an integrated wetland restoration and flood risk reduction program in the Mississippi River Delta. East of New Orleans, Biloxi Marsh, a ~1700 km2 peninsula jutting 60 km north toward the State of Mississippi is one of few Delta wetland tracts well positioned to dissipate hurricane surge and waves threatening the city’s newly rebuilt hurricane flood defenses. Both its location on the eastern margin of the Delta, and its genesis as the geologic core of the shallow water St. Bernard/Terre aux Boeuf sub-delta, which was the primary Mississippi outlet for almost 2000 years, make Biloxi Marsh attractive for restoration, now that the Mississippi River Gulf Outlet deep-draft ship channel has been dammed, and 50 years of impacts from construction and operation have abated. Now, the cascade of ecosystem damage it caused can be reversed or offset by restoration projects that leverage natural recovery and increased access to suspended sediment from the Mississippi River. Biloxi Marsh is (1) geologically stable, (2) benefiting from increased input of river sediment, and (3) could be restored to sustainability earlier and for a longer period than most of the rest of the submerging Mississippi Delta. The focus of this review is on the Biloxi Marsh, but it also provides a template for regional studies, including analysis of 2D and 3D seismic and other energy industry data to explore why existing marshes that look similar on the ground or from the air may respond to restoration measures with different levels of success. Properties of inherent durability and resilience can be exploited in restoration project selection, sequencing and expenditure. Issues encountered and investigative methods applied in the Biloxi Marsh are likely to resonate across initiatives now contemplated to sustain valuable river deltas worldwide.

Humans design infrastructure for human needs, with limited regard for the needs of nonhumans such as animals and plants. Humans also often fail to recognise nonhuman lifeforms such as trees as fellow engineers designers, or architects, even though the contribution of trees to ecosystem services is well established and their right to justice ought to be recognised. Studies have shown that flood-control infrastructure near the Mississippi River inadvertently left Southern Louisiana more vulnerable to coastal threats. We examine this characteristic outcome and identify infrastructural injustices in multispecies communities. Based on theories in philosophy and design supported by historical analyses, we defend the proposals to extend 1) the understanding of resilience to include more-than-human communities; and 2) the notion of justice to include non-human stakeholders. The reframing in more-than-human terms is already under way in a variety of disciplines. However, these efforts rarely extend into considerations of practical design and have attracted criticism for insufficient engagement with historical processes and the accumulations of power and responsibility. To illustrate these injustices, we trace the history of bald cypress trees (Taxodium distichum) in the Mississippi River Delta and show how infrastructure impacted the trees. This analysis demonstrates that designs that do not consider the needs of vulnerable stakeholders can cause harm in multispecies communities. In response, we propose that humans can work to improve infrastructural resilience by including humans and nonhumans as collaborators.

Phragmites australis is a globally distributed wetland plant. At the mouth of the Mississippi River, P. australis on natural levees of the network of distributary channels appears to increase the flow in the deep draft navigation channel, which, in turn, may reduce the sedimentation and benefit the navigation dredging. For several years, P. australis has been dying in the Mississippi River’s Bird’s Foot Delta, which appears to be shortening the distributary channels and increasing the lateral flow from the remaining portions. A conceptual model based on D-FLOW FM was applied to calculate channel sedimentation in a series of idealized deltaic systems to predict the consequences of P. australis dieback and other factors that diminish the delta complexity, such as sea-level rise and subsidence, on sedimentation in the distributary channels. Channel complexity in each system, which was quantified with an index ranging from 0 to 10 that we developed. Model results indicate that sedimentation was insensitive to the channel complexity in simple deltas but was sensitive to the channel complexity in complex deltas, such as the current Mississippi River Delta with extensive P. australis. Channel sedimentation remains stable from 0 until the channel complexity index reaches 6. In more complex deltas, the sedimentation decreases rapidly as the channel complexity increases. The sedimentation is also affected by waves, river discharge, sediment concentration, grain sizes, and bed level. River managers in Louisiana may benefit from new models based on bathymetric data throughout the Bird’s Foot Delta; data on the effects of the P. australis belowground biomass on bank erodibility across a range of current velocities; and data on the effects of P. australis stem density, diameter, and height on the lateral flow across a range of river stages and tidal stages to help them decide how much to respond to Phragmites dieback. Options include increased navigation dredging, increased restoration of the channel complexity via a thin layer of sediment deposition on natural levees and the planting of more salt-tolerant vegetation on natural levees.