Comparison of Floc Growth and Stability in Four Estuarine Clay Simulations

Wednesday, 17 December 2014
Allen H Reed1, Joseph P Smith2, William Gurzynski2 and Guoping Zhang3, (1)Naval Research Lab Stennis Space Center, Seafloor Sciences Branch, Stennis Space Center, MS, United States, (2)US Naval Academy, Oceanography Department, Annapolis, MD, United States, (3)University of Massachusetts Amherst, Department of Civil and Environmental Engineering, Amherst, MA, United States
Flocculated sediment transport is a primary determinant of hydrodynamics and geomorphology in many muddy nearshore environments which contain significant amounts of clay. In these nearshore and estuarine environments, as in most oceanic environments, the clay mineral occurrence is dominated by the following: montmorillonite (2:1 expandable), illite (2:1 non-expandable) and kaolinite (1:1 non-expandable). However, the percentages of clay minerals within these environments vary significantly. This work addresses the importance of clay mineral percentages on floc growth rates and stability. A series of analyses used four different ratios of montmorillonite, illite and kaolinite; these ratios serve to simulate the clay mineral assemblage in four different rivers. The clay minerals were mixed into saline water within which guar, a nonionic biopolymer, had previously been dissolved. Upon addition, the mixture was shaken vigorously for several minutes and then the system was allowed to settle into a quiescent environment. Flocs were maintained in a quiescent, no-flow environment until analyzed. The analyses consisted of subjecting the flocs to three flow rates within a flow through particle size analyzer, CILAS1190. For each flow rate, floc sizes were quantified and stability was inferred from changes in floc size. The flocs were analyzed during a two month period; assessments were made after 1d, 2d, 7d, 14d, 1m and 2m from the initial mixing. Results indicate that while floc size increased significantly over time, total floc stability changed less significantly. This work suggests that floc growth and stability may be achieved in a relatively short duration of time within quiescent environments. The importance of hydrodynamic stress on floc size and stability will be an important aspect for future research; subjecting flocs to hydrodynamic stress will address the importance of particle collisions and fluid-induced stress on floc size and stability.