BIOPHYSICAL COHESION AND BEDFORM DYNAMICS

In coastal environments, wave-generated oscillatory flow in the bottom boundary layer mobilizes sediment resulting in bedform generation and evolution. The presence of bedforms on a sediment bed affects sediment transport, wave attenuation, and acoustic scattering. Many studies have examined the dynamics of sediment transport and the development of bedforms on the seafloor due to the interaction of waves and currents. However, these studies have relied heavily on laboratory experiments undertaken using sands with no biological influence. The objective of this research is to understand the effects of extracellular polymeric substances (EPS) on the spatial and temporal development of bedforms in oscillatory flow environments. We hypothesize that increasing EPS levels within a sand bed will allow for increased cohesion and therefore decreased sediment transport. We anticipate that the rate of evolution will decrease, which will increase the transition time necessary for bedforms to reach an equilibrium state. Experiments will be carried out using an oscillatory flow tunnel that is 2 m long and 25 cm wide. The flow tunnel generates oscillatory flow using a piston flywheel at varying speeds and frequencies to simulate varying bottom boundary layer flow conditions. We plan to evaluate and quantify the effects of EPS on bedform dynamics by running experiments with EPS percentages ranging from 0 to 1% per dry weight of quartz sand. A laser bed profiling system will measure the three-dimensional evolution of the bed surface. An Acoustic Doppler Velocimeter (ADV) will measure the water velocity profile at one location above the bed. The inclusion of the quantifiable effects of EPS on bedform evolution rate into hydrodynamic and geologic models will benefit predictions of sediment transport, seafloor roughness, sediment stability, and underwater acoustic response.