THE IMPACT OF POLYMERS ON SEDIMENT ERODIBILITY AND ITS IMPLICATION TO SEDIMENT DIVERSION

In recent years, several studies (Hoyal and Sheets, 2009, Edmonds and Slingerland, 2010, Caldwell and Edmonds, 2014, Straub et al., 2015) have emerged which attempt to characterize the role and effects of sediment cohesion on the morphology of river channels and their respective deltas. Physical experiments have incorporated the use of an artificial partially-hydrolyzed polyacrylamide polymer, New-Drill® Plus, to enhance the cohesiveness of the sediment mixtures used. To better understand the effects of the polymer on a larger scale, the goal of our research was to characterize how erodibility of sediment was affected by the addition of polymer. Using the same sediment mixtures as those used by Straub et al., 2015, experiments were conducted with a dual-core Gust Erodibility Microcosm System (GEMS), which applies seven increasing levels of shear stress (0.01-0.6 Pa) to the cores. Three polymer concentrations were used: a sediment mixture containing no polymer, a medium polymer mixture (0.73g polymer/kg of sediment), and a high polymer mixture (1.47g polymer/kg of sediment). Cores for the GEMS experiments were mixed by hand in the laboratory, and also taken from actual physical delta experimental deposits prepared in Sediment Dynamics Laboratory of Tulane University. Preliminary results show that increased concentrations of polymer in sediment contribute to decreased erodibility, higher critical shear stress, and less eroded mass. Additionally, consolidation was also shown to have a role in sediment erodibility. Mixtures allowed to consolidate for 48 hours resulted in less eroded mass and lower erodibility, while newly mixed sediment had higher eroded mass and higher erodiblity. The results of this study have implications on how cohesive sediment plays a role in delta formation, sediment diversions and land building in areas such as coastal Louisiana, and shed light on the methods used to enhance the retention of cohesive sediment.