Influence of the Coriolis force on the velocity structure of gravity currents in straight submarine channel systems

Abstract

Large‐scale turbidity currents in submarine channels often show a significant asymmetry in the heights of their levee banks. In the Northern Hemisphere, there are many observations of the right‐hand channel levee being noticeably higher than the left‐hand levee, a phenomenon that is usually attributed to the effect of Coriolis forces upon turbidity currents. This article presents results from an analog model that documents the influence of Coriolis forces on the dynamics of gravity currents flowing in straight submarine channels. The observations of the transverse velocity structure, downstream velocity, and interface slope show good agreement with a theory that incorporates Ekman boundary layer dynamics. Coriolis forces will be important for most large‐scale turbidity currents and need to be explicitly modeled when the Rossby number of these flows (defined as Ro = ∣U/Wf∣, where U is the mean downstream velocity, W is the channel width, and f is the Coriolis parameter defined as f = 2Ω sin(θ), with Ω being the Earth's rotation rate and θ being the latitude) is less than order 1. When Ro ≪ 1, the flow is substantially slower than a nonrotating flow with the same density contrast. The secondary flow field consists of frictionally induced Ekman transports across the channel in the benthic and interfacial boundary layers and a return flow in the interior. The cross‐channel velocities are of the order of 10% of the along‐channel velocities. The sediment transport associated with such transverse flow patterns should influence the evolution of submarine channel levee systems.