Dynamics of dense gravity currents and mixing in an up-sloping and converging vee-shaped channel

Detailed velocity and density measurements are used to investigate dense water dynamics in an inclined, silled channel of triangular cross-section with varying side slope alpha and adverse bed slope phi. For the steeper channel configuration considered (phi=3.6 degrees), the dense-water bottom current is shown to be frictionally-controlled, with an internal flow structure characterized by a sharp pycnocline and decreasing isopycnal separation in the along-channel direction. For the milder up-sloping channel (phi=1.7 degrees), the dense water outflow is shown to be hydraulically-controlled as the channel sill section is approached, with internal flow dynamics characterized by increasing isopycnal separation in the along-channel direction. Analysis of the gradient Richardson number Ri(g) of the flow confirms that hydraulically-controlled flows dilute the active bottom water due to interfacial mixing. A gradually-varying internal flow model and a two-layer hydraulic modelling approach are shown, respectively, to represent adequately the outflow behaviour for these two bed slope conditions.