I have seen an Ec 135 come in and do a downwind quickstop, as he rolled on the bank and pulled round to come into wind he shed a vortex from the blades. This vortex touched down on the disused runway and started to pick up debris. It sustained itself for 10 to 15 seconds drifting downwind with this debris. The taxiing aircraft had almost made it to the dispersal before the vortex disappeared. I dare say a Sea King could do similar, but on a larger scale! It may be time for air traffic to bring in approach separation for Rotary too.