Doctor of Philosophy (PhD)
Civil and Environmental Engineering
This dissertation tests the hypothesis that the early phases of deltaic bar and distributary channel formation and sediment transport on an adverse slope could be simulated with a 2D finite element sediment transport model. The models used were RMA2 and SED2D modules of the TABS-MD model suite. A finite element mesh of the lower Atchafalaya River and the delta was developed, using the Surface Water Modeling System (SMS) software package. Calibration and validation of the model were performed, using data collected during field surveys and from available Atchafalaya River archived flow, suspended sediment, and dredging records. In a test simulation in which adequate flow and sediment supply were provided in large quantity, sub-aqueous distributary mouth bar formed at the end of the feeder channel. As simulation continued, a more prominent distributary channel and sub-aerial levees were developed. When the model was changed to impose a no flood conditions on high points, formation of new distributary channels was observed. The same model was used to determine a self-sustainable adverse slope or sediment ramp that could be used to divert sediments efficiently in a deltaic setting similar to the Atchafalaya Bay. A test slope of 1V to 51H was used in the model. After several simulations, the model tends to produce a much milder slope close to 1V to 412H. Five adverse natural slopes observed in the Wax Lake Outlet delta were compared with the model-suggested slopes. Adverse slopes at the Wax Lake Outlet delta varied from 1V to 340H – 850H, with 1V to 543H as the average. Finally, a calibrated model of the Atchafalaya River and the delta was applied to develop a set of sedimentation/erosion curves that could be used by the engineers to estimate scour and deposition for proposed artificial feeder channels. These curves suggest that a discharge of at least 11,325 cms (400,000 cfs) at Morgan City is necessary to transport sand into the delta. It was observed that even for a very high flood, sand deposition should be limited to within 1000 m (3281 ft) of distributary channel mouths.
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Mashriqui, Hassan Shahid, "Hydrodynamic and sediment transport modeling of deltaic sediment processes" (2003). LSU Doctoral Dissertations. 1483.
Joseph N. Suhayda