Density surges: two-dimensional experiments

Some new aspects of the development of density surges in channels are developed from recent experimental results. A density surge is characterized by the flow of a finite amount of dense fluid. This dense fluid may be a saline-water solution, a saline-water solution with tracers (sand in suspension) or a pure suspension (sand in suspension in fresh water). The experimental results show in particular that: (1) the velocity of the surge is effectively proportional to the square root of the initial volume, (2) the velocity of the surge increases with the increase of the initial density of the heavy fluid, proportionally to the square root of the ratio of density difference to the ambient fluid density, (3) the speed of the surge increases again with an increase of the slope. For pure suspensions the experiments show that velocities slow down much more quickly than for saline solutions with the same initial density, due to loss of negative buoyancy. The effects of the initial density and of the size of the grains on the distribution of sediments are described.