Optimizing Sediment Diversion Operations: Working Group Recommendations for Integrating Complex Ecological and Social Landscape Interactions

Abstract

Future conditions of coastal Louisiana are highly uncertain due to the dynamic nature of deltas, climate change, tropical storms, and human reliance on natural resources and ecosystem services. Managing a system in which natural and socio-economic components are highly integrated is inherently difficult. Sediment diversions are a unique restoration tool that would reconnect the Mississippi River to its deltaic plain to build and sustain land. Diversions are innately adaptable as operations can be modified over time. An expert working group was formed to explore how various operational strategies may affect the complex interactions of coastal Louisiana's ecological and social landscape and provide preliminary recommendations for further consideration and research. For example, initial operations should be gradually increased over 5 to 10 years to facilitate the development of a distributary channel network, reduce flood risk potential to communities, limit erosion of adjacent marshes and reduce stress to vegetation and fish and wildlife species. Diversions should operate over winter peaks to capture the highest sediment concentration, reduce vegetation loss while dormant, and reduce detrimental effects to fish and wildlife. Operations during the spring/summer should occur over shorter periods to capture the highest sediment load during the rising limb of the flood peak and minimize impacts to the ecosystem. Operational strategies should strive to build and sustain as much of the coastal landscape as possible while also balancing the ecosystem and community needs.

Quantifying the Relative Importance of Riverine and Open‐Ocean Nitrogen Sources for Hypoxia Formation in the Northern Gulf of Mexico

“…In relation to our discharge diversion scenario, it is important to note that the diversion from the Mississippi River toward the Atchafalaya River applied here may not be practical and differs from potential diversions investigated in other studies (e.g., Allison & Meselhe, 2010;Peyronnin et al, 2017) and considered by Louisiana's Coastal Protection and Restoration Authority (CPRA, 2017). The latter consider diversions of water from both Mississippi and Atchafalaya Rivers toward wetlands, such as Barataria Bay or Terrebonne Bay.…”

A faithful record of channel mouth bifurcation angles in river delta stratigraphy on Earth and Mars

“…This highlights the remarkable stability of channel mouth bifurcation angles after they are initiated, through network evolution, abandonment and stratigraphic preservation. These findings can be applied to modern deltas as evidence that distributary channel networks building from channel mouth bifurcations are unlikely to significantly rearrange their networks over centennial timescales associated with engineered diversions (Kim et al, 2009, Peyronnin et al, 2017.…”

Patterning emergent marsh vegetation assemblages in coastal Louisiana, USA, with unsupervised artificial neural networks

“…Incumbent upon nearly all ecosystem restoration and management programs is the need for predicting and monitoring ecosystem responses to natural variability, disturbance, and anthropogenic impacts, often as they relate to changes in species composition. In coastal wetlands of Louisiana, increased inundation is expected to accompany increased freshwater inflows (Snedden, Cable, & Wiseman, ) brought about by Mississippi River diversions designed to reintroduce sediments to the rapidly subsiding delta plain (Peyronnin et al., ). Excessive inundation has been shown to impede belowground marsh production of community dominants in regions where river diversions are being planned (Snedden et al., ), which can diminish organic soil accumulation, the primary contributor to marsh vertical accretion in the inactive regions of the Mississippi River delta plain (Cahoon, White, & Lynch, ; DeLaune, Kongchum, White, & Jugsujinda, ; DeLaune, Whitcomb, Patrick, Pardue, & Pezeski, ; Nyman, DeLaune, Roberts, & Patrick, ; Turner, Swenson, & Milan, ).…”

“…Excessive inundation has been shown to impede belowground marsh production of community dominants in regions where river diversions are being planned (Snedden et al., ), which can diminish organic soil accumulation, the primary contributor to marsh vertical accretion in the inactive regions of the Mississippi River delta plain (Cahoon, White, & Lynch, ; DeLaune, Kongchum, White, & Jugsujinda, ; DeLaune, Whitcomb, Patrick, Pardue, & Pezeski, ; Nyman, DeLaune, Roberts, & Patrick, ; Turner, Swenson, & Milan, ). As such, the success of these projects may largely hinge upon the ability of existing marsh vegetation communities to self‐organize around conditions of increased inundation (Peyronnin et al., ) and thus there exists a need to continuously classify new samples of species composition data into these community types as new data become available. Traditional unsupervised clustering techniques are unstable to the addition of new data, as shifts in cluster membership of previously classified sites may occur when new samples are added to previously classified datasets.…”

“…The wetlands in coastal Louisiana along the northern Gulf of Mexico account for roughly 40% of all the wetlands in the continental United States and have exhibited high rates of land loss over the last century, during which roughly 5,000 km 2 of land has transitioned to open water (Couvillion, Beck, Schoolmaster, & Fischer, ) largely due to a combination of submergence and diminished sediment supply (Penland et al., ). The region is now the subject of a globally unprecedented ecosystem restoration program estimated to cost $50–100 billion over the next 50 years (Peyronnin et al., ). Plant communities often reflect ecosystem processes and conditions at local and landscape scales more effectively than any other set of factors (Albert & Minc, ), and different communities can influence processes such as hydrodynamics (Leonard & Luther, ), vertical accretion (Pasternack & Brush, ), and carbon burial (Wang, Xu, & Rongrong, ) in distinct ways.…”