Natural Processes in Delta Restoration: Application to the Mississippi Delta

Abstract

Restoration of river deltas involves diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. Except for local engineered structures at the points of diversion, restoration mainly relies on natural delta-building processes. Present understanding of such processes is sufficient to provide a basis for determining the feasibility of restoration projects through quantitative estimates of land-building rates and sustainable wetland area under different scenarios of sediment supply, subsidence, and sea-level rise. We are not yet to the point of being able to predict the evolution of a restored delta in detail. Predictions of delta evolution are based on field studies of active deltas, deltas in mine-tailings ponds, experimental deltas, and countless natural experiments contained in the stratigraphic record. These studies provide input for a variety of mechanistic delta models, ranging from radially averaged formulations to more detailed models that can resolve channels, topography, and ecosystem processes. Especially exciting areas for future research include understanding the mechanisms by which deltaic channel networks self-organize, grow, and distribute sediment and nutrients over the delta surface and coupling these to ecosystem processes, especially the interplay of topography, network geometry, and ecosystem dynamics.

Climate change: Protect the world's deltas

“…The proportion of sediment that ends up on and off shore is poorly quantified [4][5][6] . The majority is washed away because delta plains are inefficient sediment traps; even more so when they host engineered infrastructure.…”

“…Maintenance strategies can limit delta drowning 4,5 . These include boosting sediments in river waters, diverting them before they reach the coast, optimizing the trapping abilities of the delta plain and keeping wetlands healthy 2,4,5-9 .…”

“…Multiple channels can be dug to spread sediments across the delta plain 5 and build marshes, fill ponds and extend lobes 4 . Deliberately breaching levees during floods or redirecting a river to fill basins can enhance natural backwater effects and promote wetland formation.…”

The morphology and evolution of channels on the Wax Lake Delta, Louisiana, USA

“…Such deposits border lakes and oceans and support large human populations and productive ecosystems. River deltas react dynamically to both external and internal forcing [Heller et al, 2001;Sheets et al, 2002;Kim et al, 2006;Paola et al, 2011], strongly affecting human communities by their responses to contemporary and future environmental change [Syvitski and Saito, 2007;Syvitski et al, 2009]. Predictive understanding of delta evolution is therefore a valuable tool to forecast future deltaic change and for justifying delta stewardship strategies [Day et al, 2007;Kim et al, 2009;Paola et al, 2011].…”

“…The aim of this study is to characterize channel network evolution of the WLD, a rapidly prograding river delta that nevertheless exhibits systematic channel widening and erosion into bedrock composed of consolidated mud. The WLD's progradation is especially important because it has occurred with little human modification after the initial dredging of its feeder channel, and is frequently cited as an analog for new land-building diversions considered for restoration of the greater Mississippi Delta [Kim et al, 2009;Allison and Meselhe, 2010;Paola et al, 2011;Allison et al, 2012]. We investigate channel network evolution on the WLD by measuring (1) the topographic and planimetric evolution of the Wax Lake Delta and its feeder channel over decadal scales, (2) the character of the channel bed, and (3) (Figure 2).…”