Showing papers by "Denise J. Reed published in 2019"

Mitigating the Effects of Sea-Level Rise on Estuaries of the Mississippi Delta Plain Using River Diversions

Abstract: Using the Mississippi River as a tool for restoration has been a key element of restoration planning in Louisiana for decades. The results of allowing river water and sediment back into the coastal system are manifested in a number of places in present day Louisiana, with additional plans for large scale sediment and water diversions from the Mississippi River. Many previous numerical modeling studies have focused on sediment delivery to Louisiana estuaries. This study examines the effects of river diversions on salinity gradients in receiving estuarine basins. The Integrated Compartment Model, a planning-level model that simulates multi-decadal change in estuarine hydrodynamics and wetland systems under assumed sea-level rise scenarios, was used to assess the estuarine salinity gradient under potential management regimes. The simulations for current conditions are compared to a future 50-year simulation with additional diversions, as well as cases with a variety of diversion options. This modeling analysis shows that without additional action, 50-years of sea-level rise could result in substantial increases in salinity throughout the Mississippi Delta Plain estuaries. This can be largely offset with additional large river diversions which can maintain variable salinity gradients throughout the estuary basins.

Modeled Sediment Availability, Deposition, and Decadal Land Change in Coastal Louisiana Marshes under Future Relative Sea Level Rise Scenarios

Abstract: The ability, or lack thereof, for wetlands in coastal Louisiana to maintain elevation capital has been well documented in the literature to be a function of local and regional factors as well as environmental conditions. The Integrated Compartment Model (ICM) framework developed for the state of Louisiana’s Coastal Master Plan models hydrologic, vegetation, and wetland elevation dynamics and captures regional and local dynamics of wetland elevation, inundation and sedimentation processes. It provides insights into the relative sensitivities of wetland evolution to environmental drivers under uncertain future environmental conditions. A systematic, and computationally efficient modeling exercise was conducted to test coastal marsh survival across a wide range of possible future relative sea level rise rate scenarios. Model results indicate a diverse response with respect to sediment deposition and marsh survival driven by regional subsidence rates and proximity to suspended sediment sources. Sediment poor regions of coastal Louisiana are particularly sensitive to relative sea level rise under all but the most optimistic of future sea level rise rates simulated. Coastal marshes with high sediment availability fare much better under most scenarios tested, despite high rates of relative sea level rise.

Linking management planning for coastal wetlands to potential future wave attenuation under a range of relative sea-level rise scenarios.

Abstract: Understanding changes in wave attenuation by emergent vegetation as wetlands degrade or accrete over time is crucial for incorporation of wetlands into holistic coastal risk management. Linked SLAMM and XBeach models were used to investigate potential future changes in wave attenuation over a 50-year period in a degrading, subtropical wetland and a prograding, temperate wetland. These contrasting systems also have differing management contexts and were contrasted to demonstrate how the linked models can provide management-relevant insights. Morphological development of wetlands for different scenarios of sea-level rise and accretion was simulated with SLAMM and then coupled with different vegetation characteristics to predict the influence on future wave attenuation using XBeach. The geomorphological context, subsidence, and accretion resulted in large predicted reductions in the extent of vegetated land (e.g., wetland) and changes in wave height reduction potential across the wetland. These were exacerbated by increases in sea-level from +0.217 m to +0.386 m over a 50-year period, especially at the lowest accretion rates in the degrading wetland. Mangrove vegetation increased wave attenuation within the degrading, subtropical, saline wetland, while grazing reduced wave attenuation in the temperate, prograding wetland. Coastal management decisions and actions, related to coastal vegetation type and structure, have the potential to change future wave attenuation at a spatial scale relevant to coastal protection planning. Therefore, a coastal management approach that includes disaster risk reduction, biodiversity, and climate change, can be informed by coastal modeling tools, such as those demonstrated here for two contrasting case studies.

Wetland transitions and loss in coastal Louisiana under scenarios of future relative sea-level rise

Abstract: Coastal Louisiana encompasses a vast expanse of wetland ecosystems that are subject to a number of historic, ongoing and future stressors including natural and human indices subsidence, hydrologic alteration and eustatic sea level rise. Predictions of future eustatic sea level rise indicate an uncertain future for coastal marsh survival. Model simulations conducted for the 2017 Louisiana Coastal Master Plan enabled assessment of land loss drivers under assumed future conditions reflected in three scenarios: low, medium and high. Output data generated by the Integrated Compartment Model, consisting of several integrated models reflecting hydrologic, vegetative and morphological change, were post-processed to diagnose the causes of conversion of wetland to open water for 50-year future simulations. Wetland conversion to open water was determined by wetland type (e.g., fresh, brackish salt) according to threshold conditions for marsh collapse associated with excess salinity (fresh wetlands) or inundation (non-fresh wetlands). Historic marsh edge erosion rates were projected into the future which also resulted in conversion of wetland to open water.