an incident that was potentially catastrophic for london occurred on 27 october 1997. the dredger, mv "sand kite", sailing in thick fog, collided with one of the thames barrier's piers. as the ship started to sink she dumped her 3,300 tonne load of aggregate, finally sinking by the bow on top of one of the barrier's gates where she lay for several days. initially the gate could not be closed as it was covered in a thick layer of gravel. a longer term problem was the premature loss of paint on the flat side of the gate caused by abrasion. one estimate of the cost of flooding damage, had it occurred, was around £13 billion. the vessel was refloated in mid-november 1997.