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Dynamics of a Large Shelf Discharging River: Implications for Coastal Sedimentology and Restoration

Alexander Kolker, Alex Ameen, Georgia Boxer, Chunyan Li, Chet Pilley, Cyndhia Ramatchandirane, and Nan Walker
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Rivers are the primary means by which water, sediments, and land-derived dissolved material are transported from the continents to the ocean. However, relatively little is known about the dynamics of large shelf discharging rivers, and the differences between shelf discharging river and deep water discharging rivers, particularly with respect to the distribution of sediments in the coastal zone. The great Mississippi/Atchafalaya River Flood of 2011 provided an excellent opportunity to examine the impacts of a large, shelf-discharging river on the coastal ocean, and the role that such rivers play in the development of marine stratigraphic sequences. Vessel-based surveys were conducted along the Atchafalaya and Mississippi River Shelves, which collected data that included in situ measurements of salinity, temperature, dissolved oxygen, turbidity, particle size, and horizontal current velocity profiles along the vertical, as well as remotely sensed images of the river plumes. The Atchafalaya River plume produced intense gradients in temperature, salinity, oxygen and turbidity, including periods of meta-stable temperature inversions that were not observed along the Mississippi River Shelf. This event also produced massive sedimentation on the inner continental shelf fronting the Atchafalaya River, which likely reflects changes of patterns of sediment distribution, rather than major changes to the annual sediment budget during the flood. These results suggest that future coastal restoration efforts should focus on constraining sediments to the near-shore zone, and that extreme events may not be the ideal analogue for coastal restoration. Understanding patterns of organic rich, fine grained sediment distribution may also be useful for understanding reservoir formation

AAPG Search and Discovery Article #90167©2013 GCAGS and GCSSEPM 63rd Annual Convention, New Orleans, Louisiana, October 6-8, 2013