Assessing Changes in River Stage Of Specific Discharge Along the Lowermost Mississippi River

Sanjeev Joshi, Louisiana State University, Baton Rouge, LA 70803: sjoshi2@tigers.lsu.edu; Y. Jun Xu, Louisiana State University, Baton Rouge, LA 70803: yjxu@lsu.edu

Comprehensive analysis of long-term river stage (RS) changes can improve our understanding of sediment deposition and erosion in river channels. In this study, we investigated 28-year long (1987-2015) changes in the river stages of specific discharge along the 320-km LmMR reach from the Old River Control Structure to New Orleans. River stage records were gathered from eight locations: Tarbert Landing (TBL), Red River Landing (RRL), Bayou Sara (BS), Baton Rouge (BTR), College Point (CP), Reserve (RES), Bonnet Carre (BC), and Carrolton (CAR). Mean annual RS at all locations were analyzed based on four specific daily discharge types at TBL (since RS for a given day at the locations indicated discharge at TBL for that day): 10000 cms (9000 ≤ Q ≤ 11000 cms); 15000 cms (14000 ≤ Q ≤ 16000 cms); 20000 cms (19000 ≤ Q ≤ 21000 cms); and 25000 cms (24000 ≤ Q ≤ 26000 cms). An increasing trend of RSs reflects sediment accumulation at a location, while a decreasing trend of RSs indicates riverbed erosion. We found that RS of all specific discharge increased at RRL and BTR, but decreased for two flow types at BS (15000 and 20000 cms). RS trends were mostly either inconclusive or constant for all other locations further downstream. Hence, based on these trends we conclude that LmMR has most probably accumulated sediments in ~ 2 km reach from TBL to RRL and further down at BTR, while eroded them at BS over the past two decades. Also, at sites downstream from BTR, sediment deposition over time seems either inconclusive or negligible.

Key words: lowermost Mississippi River, specific discharge, river stage, sediment accumulation and erosion

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