The airport did do something. Before they installed permanent concrete sandbags and paving slabs to direct water from above, heavy rain used to wash mud and rocks onto the road below.
I can remember when the tunnel first opened and seeing a car that was all but submerged. In those days though the old access route was still open so it caused no disruption.
Could not an emergency road crossing be provided across the taxiway between the bridge and the fire station? No doubt I will be ridiculed here but in Gibraltar the main road onto the rock crosses the Runway.