The Thames Estuary is the estuary in which the River Thames meets the waters of the North Sea, in the south-east of Great Britain. It is not easy to define the limits of the estuary. Although physically the head of Sea Reach or the KentHam. The Nore is a sandbank at the mouth of the estuary, between Havengore Creek, Essex, and Warden Point, Kent. The eastern boundary of the estuary suggested in a Hydrological Survey of 1882-9 is a line drawn from North Foreland, Margate, Kent via the Kentish Knock lighthouse to Harwich in Essex. It is to this line that the typical estuarine sandbanks extend. The estuary downstream of the Tideway has a tidal movement of 4 metres, moving at a speed of 8 miles per hour.