Simulating Turbidity Current Dynamics Using Natural Topographies With and Without Clear-Water Entrainment

This study uses a modified version of Parker et al. (1986)'s one-dimensional turbidity current model to simulate the dynamics of currents that traverse natural submarine topographies, in an effort to determine if such flows might plausibly traverse channel forms currently observed at the seafloor or in shallow seismic datasets. To accomplish this, we calculated flow dynamics based on 50000 sets of initial conditions that were drawn randomly between prescribed bounds, and identified those starting conditions that allowed flows to traverse the naturally observed systems. In addition to examining the along-channel runout lengths of these flows, we used flow height and maximum velocity to rule out initial conditions that created flows that would be broadly accepted as unphysical. We found that when the clear-water entrainment rules of Parker et al. (1987) were used, a small percentage of flows (2.3-9.7%) traversed the measured portion of these natural systems and maintained physically plausible peak depth-averaged velocities. However, flows meeting these criteria nonetheless reach peak heights that were many times that of the channel-bottom to levee-crest relief. Often the height of the simulated turbidity current exceeded this channel relief by as much as an order of magnitude. When clear-water entrainment was removed from the model, a larger percentage of flows traversed the measured channel geometries, and maintained more physically plausible ranges of peak depth-averaged velocities and heights. We speculate that the unphysical flows produced using clear-water entrainment may arise due to the model's neglect of flow loss through flow stripping and/or overbank collapse, or scaling problems associated with extrapolating laboratory-measured clear-water entrainment rules to the field. Future studies that aim to account for fluid mass loss by lateral collapse and extract the clear-water entrainment relationship independently of laboratory experiments may be necessary to accurately model turbidity current dynamics at the field-scale.