Identifier

etd-07072017-004529

Degree

Doctor of Philosophy (PhD)

Department

Renewable Natural Resources

Document Type

Dissertation

Abstract

The Mississippi River delta is facing severe land loss. An urgent need exists to examine sediment transport and channel morphology dynamics along this highly engineered alluvial river that has shaped and will continue to shape its delta. This dissertation research focuses on investigating channel morphology dynamics and sediment transport in the recent three decades along a 327-km reach (from about 492 to 167 km upstream from the river’s outlet in the Gulf of Mexico) of the Lowermost Mississippi River (LmMR). The specific objectives of this research were to: 1) analyze riverbed adjustment, i.e., channel-bed aggradation or channel erosion at seven locations along the 327-km LmMR reach over the last three/four decades; 2) determine suspended sand availability under various discharge regimes at Tarbert Landing (the uppermost location of LmMR) during the period between 1973 and 2013; and 3) quantify bedload at Tarbert Landing, St Francisville and Baton Rouge (three uppermost locations of LmMR) and suspended load at St Francisville and Baton Rouge over the last one to four decades. This research found that the first 20–25 km LmMR reach below its diversion to the Atchafalaya River and the reach from ~ 80 to 140 km experienced significant riverbed aggradation, while the reach in between (i.e. from ~ 25 to 80 km) experienced riverbed degradation over the last three/four decades. The lower 187-km reach (i.e. from 140 to 327 km) showed higher sediment outflow and negligible sediment trapping. Furthermore, the LmMR discharged an average annual sand load (SLs) of 27 million tons (MT) during 1973 and 2013, at Tarbert Landing, varying largely from 3.4 to 52.3 MT. Also, during the four decades, the LmMR at Tarbert Landing carried about 71% of the total annual sand load in about 120 days each year, when the discharge was ≥ 18000 cubic meters per second (cms). The bedload transport rates along the LmMR gradually increased from Tarbert Landing [83 million tons (MT) during 2004-2015 for grain size of 0.125 mm] to Baton Rouge (at 367.5 rk) (96 MT during 2004-2014 for the same grain size). However, the total sediment supply (bedload + suspended sediment load) was substantially higher at Tarbert Landing (931 MT) and lower and nearly equal at the other downstream locations (550 MT at St Francisville and 544 MT at Baton Rouge) during 2004-2010 (the matching period of availability for both bedload and suspended load). These findings have relevant implications for the management of river-sediment diversions along the LmMR and other large alluvial rivers in the world. They could help determine specific sediment trapping sites and the development of land building schemes.

Date

2017

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Xu, Y. Jun

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