Gravity currents flowing over a rough bed

Lock-exchange gravity currents experiments are performed to characterize the influence of bottom roughness on the dense flow through Particle Image Velocimetry, PIV. The surface properties over which gravity currents propagate in natural environments play a key role in the dynamics and structure of dense current. Roughness was introduced by an array of obstacles that may slow down the gravity current and significantly modify its capacity to entrain sediments compared to a current propagating over a flat bottom. The instantaneous maps of the flow velocity show how the bottom roughness impacts the flow dynamics; as an example recirculation zones develop among the elements. These structures, are constant over time with a longitudinal development and height depending on the height of the elements; the greater the height of the elements and the greater the size of the recirculation areas.