acase@tulane.edu / Land-surface subsidence can be a major contributor to the relative sea-level rise that is threatening many coastal communities. Loosely constrained subsidence rate estimates across the Mississippi Delta make it difficult to differentiate between subsidence mechanisms and complicate modeling efforts. New data from a nearly 40 m long, 12 cm diameter core taken during the installation of a subsidence monitoring superstation near the Mississippi River, southeast of New Orleans, provides insight into the stratigraphic and geotechnical properties of the Holocene succession at that site. Stratigraphically, the core can be grouped into four units. The top 12 m is dominated by clastic overbank sediment with interspersed organic-rich layers. The middle section, 12-35 m, consists predominately of mud, and the bottom section, 35-38.7 m, is marked by a transition into a Holocene-aged basal peat (~11.3 ka) which overlies densely packed Pleistocene sediment. Radiocarbon and OSL ages are used to calculate vertical displacement and averages subsidence rates as far back as ~3.5 ka, yielding values as high as 8.0 m of vertical displacement (up to 2.34 mm/yr) as obtained from a transition from mouth bar to overbank deposits. We infer that most of this was due to compaction of the thick, underlying mud package. The top ~80 cm of the core is a peat that represents the modern marsh surface and is inducing minimal surface loading. This is consistent with the negligible shallow subsidence rate as seen at a nearby rod-surface elevation table – marker horizon station. Future compaction scenarios for the superstation can be modeled from the stratigraphic and geotechnical properties of the core, including the loading from the planned Mid-Barataria sediment diversion which is expected to dramatically change the coastal landscape in this region. / 1 / Jonathan G Bridgeman

This study investigates the Louisiana 2012 Coastal Master Plan’s ability to reconcile conflicting economic and ecological demands on coastal resources. The Louisiana Coastal Master Plan was unique in combining flood control and coastal restoration under one authority. However, the objectives of flood control and coastal restoration can be in conflict. The plan was also unique in its approach of restoration from a working coast perspective. However, the objectives of ecological restoration and economic productivity do not always agree. By conducting semi-structured interviews with major coastal stakeholders, this research will explore how the planning process has accommodated the views and values of key stakeholder parties. This research aims to make more transparent the inherent environmental tradeoffs of restoration from a working coast perspective. A working coast is a compromise between economic and environmental stakeholder needs. The approach requires a balance of power to ensure that the projects selected best serve the needs of all parties. The study found that while there is industry buy in, mechanisms for mitigating economic externalities is lacking in the plan, corporate infrastructure benefits while wildlife resources are in decline.