 As a result of the accumulation of mud and silt in the harbour, ships entering the narrow harbour were frequently being grounded.In 1832 Brunel was called upon to provide the solution to this problem and designed the sluice system, still in use today, to remove excesses of silt and mud.In place of the Overfall he constructed three shallow sluices and one deep scouring sluice, between the harbour and the New Cut, together with a dredging vessel, known as a drag boat, to scrape the silt away from the quay walls.