River Thames Thames Estuary), the river is subject to tidal activity from the North Sea. Before the lock was installed, the river was tidal as far as Staines, about upstream. London, capital of Roman Britain, was established on two hills, now known as Cornhill and Ludgate Hill. These provided a firm base for a trading centre at the lowest possible point on the Thames. A river crossing was built at the site of London Bridge. London Bridge is now used as the basis for published tide tables giving the times of high tide. High tide reaches Putney about 30 minutes later than
Mardyke (river) Mardyke (river) The Mardyke (sometimes, but less frequently, Mar Dyke, occasionally Mardike) is a small river, mainly in Thurrock, that flows into the River Thames at Purfleet, close to the Queen Elizabeth II Bridge. In part, it forms the boundary between the Essex hundreds of Barstable and Chafford. The river gives its name to the Mardyke Valley—a project aimed at increasing appreciation and usage of recreational land around the Mardyke. The main source of the Mardyke is in Holden's Wood between Great Warley and Little Warley. It flows roughly from the source to the Tideway of the Thames at Purfleet,