Degree

Doctor of Oceanography and Coastal Sciences (POCS)

Department

Department of Oceanography and Coastal Sciences

Document Type

Dissertation

Abstract

Deltas worldwide share the same sinking problem in face of pressure from natural and anthropogenic activities. Many restoration strategies are being planned or have been implemented in the coasts around the world. However, many conventional hard structure constructions are energy-intensive. There are also associated uncertainties and limitations on the effectiveness and sustainability of these restoration plans. Soft or ecological engineering strategies normally take advantage of or mimic the coastal system self-response and feedbacks to natural and anthropogenic activities. The successful implementation of soft strategies relies on process-based studies on the change of complex coastal system. In addition, post-implementation monitoring work is also highly needed to evaluate the effectiveness of restoration strategies.

Taking the Mississippi deltaic coast as an example, this dissertation aims to provide information for restoration strategy planning and implementation, as well as to help improve coastal resource management. A total of three contrasting deltaic plain, estuarine and inner continental shelf sedimentary environments are investigated, with a time scale ranging from days to hundreds of years. The mainly findings are: (1) four lithofacies of Plaquemines sub-delta lobe are identified in Lower Breton Sound. A ~60 cm relative sea level rise is recorded in the cores during 950-1250 A.D., after which the rate of relative sea level change kept increasing at eastern Mississippi deltaic coast. (2) Bay hydrodynamics and its impacts on micro-tidal wetland are monitored at Fourleague Bay, near Atchafalaya River mouth. Wind-driven waves mainly cause benthic sediment resuspension in the bay, whose available flux for surrounding marsh varies from 0 to 500 g·m-1·s-1. Seasonal variations of river discharge and wind direction greatly impact potential sediment contribution from bay to adjacent wetlands. (3) Post-dredge monitoring and modeling work have been done at a mud-capped dredge pit, Sandy Point, western Mississippi bird foot delta. Limited resuspension exists on the adjacent seabed around the pit under fair weather condition, and wave induced wall collapse is restricted to a few meters per year. Current adjustment over the pit is not obvious under fair weather, and the related pit margin erosion or migration is limited.

Date

2-8-2018

Committee Chair

Xu, Kehui

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