Movie S2.

The flow over an SHS with conditions almost identical to those in Movie S1 (see Movie S1 legend for details), except that the right-hand side grating here is flooded, to contrast the different behavior observed when stopping the background pressure gradient. Similar to the flow above a ridge, the flow in the wetted grating stops immediately at the end of the loading phase, showing no backflow (this corresponds to experiments 2-4 in Table S6).