On gravity currents over changing topography

We present experimental results on continuously supplied and well developed gravity currents moving from horizontal to concave or constant-slope boundaries. Results show that the gravity current velocity is in continuous spatial development and approaches an equilibrium state velocity only when the slope change is small. Following closely the theory of Turner (1973) we derive a general equation for the depth-integrated velocity including a variable slope angle and all forcing and dissipation sources. The comparison of this equation with the experimental data reveals that bottom friction can be very large in the region of appearance of the KH billows and of the same order of magnitude as entrainment. The comparison with currents on straight slopes reveals that the results are independent of bottom curvature and demonstrates that the current continuously adjusts to the gradual slope changes.