In central Bristol, where the river is tidal, it is diverted from its original course into the New Cut, a channel dug between 1804 and 1809 at a cost of £600,000.[31] The original course is held at a constant level by lock gates (designed by Jessop) and is known as the Floating Harbour. The Floating Harbour is protected by an 1870s replacement for Jessop's locks. This unusual dock has a tentacled plan resulting from its origins as the natural river course of the Avon and its tributaries, the River Frome and Siston Brook, and is intimately entwined with Bristol's city centre as few docks are.