Gravity current propagation up a valley

12 Sep 2017

The advance of the front of a dense gravity current propagating in a rectangular channel and V-shaped valley both horizontally and up a low slope is examined through theory, full-depth lock-release laboratory experiments and hydrostatic numerical simulations. Consistent with theory, experiments and simulations show that the front speed is relatively faster in the valley than in the channel. The front speed measured shortly after release from the lock is 5% to 22% smaller than theory with greater discrepancy found in up-sloping V-shaped valleys. By contrast, the simulated speed is about 6% larger than theory showing no dependence on slope for rise-angles up to θ = 8◦. Unlike gravity currents in a channel, the current head is observed in experiments to be more turbulent when propagating in a V-shaped valley. The turbulence is presumably enhanced due to the lateral flows down the sloping sides of the valley. As a consequence, lateral momentum transport contributes to the observed lower initial speeds. A WKB-like theory predicting the deceleration of the current as it runs upslope agrees remarkably well with simulations and with most experiments, within errors.