Degree

Doctor of Philosophy (PhD)

Department

Department of Geography and Anthropology

Document Type

Dissertation

Abstract

The Lower Mississippi River is one of the most highly engineered rivers in the world. The river is now completely regulated by a combination of levees, artificial cutoffs, bank revetments, and dike fields; however, the river engineering has also complicated the geomorphological response to the sediment brought in the river. This dissertation research examined morphodynamics of the middle portion of the Lower Mississippi River from Vicksburg, Mississippi (river kilometer: 737) to Red River Landing, Louisiana (river kilometer: 486) to elucidate river engineering effects on sediment transport, storage, and distribution. The Old River Control Structure (ORCS) diverts approximately 25% of the Mississippi River into the Atchafalaya River. Hence, the research also assessed the river diversion on downstream channel morphology and sediment deposition. Results showed that the highly regulated river favored the development of mid-channel and attached bars. The average volume of a single mid-channel bar is over twice that of an attached bar and over four times that of a point bar. Overall, in the past three decades, the total volume of the 30 bars between Vicksburg and ORCS has increased by 110,118,000 m3 or 41%. Increased dike length contributed significantly to the bar volume increase. Downstream of the ORCS, three bars had a net volume gain of 30,271,000 m3 (206%). Sediment trapping on the bars was prevalent during the period 1990-1995 and 2007-2011 when large floods occurred. In particular, a single flood in the spring of 2011 increased the volume of these three bars by 1.22 × 106 m3 (4.4%). In the past 30 years, the 33 emerged channel bars along the 258-km reach trapped 168 MT sediment and currently, the total mass of their emerged portions accounts to 584 MT. These findings show that river engineering in the Lower Mississippi River has greatly affected sediment transport and deposition patterns. As a potentially useful resource for coastal protection and restoration of the sediment-starving Mississippi River Delta, future river management should develop engineering strategies to mobilize the tremendous sediment store downstream of the river.

Date

11-1-2017

Committee Chair

Wang, Lei

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