Assessment of Long-Term Changes in River Stage of the Lowermost Mississippi River

Long-term changes in river stage can reflect dynamics of river beds. Such changes in the lower reach of a river entering the sea can also indicate sea level rise and land subsidence. The lowermost Mississippi River has experienced changes in its stages over the past several decades which, however, have not been studied yet. Comprehensive analysis of long-term changes in stages of this river can aid in understanding its route downstream and differentiate between sediment erosion and deposition mechanics at several of its sites. In this study, we utilize long-term records on river stages along a 320-km reach of the lowermost Mississippi River from the Old River Control Structure to New Orleans in order to assess the channel dynamics of the highly engineered river. Eight locations along the reach are selected, including Red River Landing, Bayou Sara, St. Francisville, Baton Rouge, Dolandsonville, College Point, Bonnet Carre, and Carrolton. River stages at the locations are analyzed under the low-, medium-, and high-flow conditions over the past three decades. Changes in slope of the river stages between these locations are determined based on difference in their river stages and length of their reach. Preliminary results from this study show that the river stages drop systematically as the river moves downstream. The drop is very low from Red River Landing to Baton Rouge; it suddenly increases from Baton Rouge to the next site at Bonnet Carre, then decreases for the next few sites up to Carrolton. We also found that some river reaches experienced deposition while other river reaches had erosion during the past decades. This paper will present major findings in long term changes in lowermost Mississippi river stages and their slopes. It will also discuss implications of these findings for sediment accumulation and possible river diversion locations.