place to enable dredging to keep the advertised minimum channel depth. Ownership and operation In 1908 an Act transferred responsibility for all points of the river downstream of a point below Teddington Lock to the Port of London Authority thereby including this structure. Reasons for construction When the London Bridge of 1209 to 1831 was demolished the removal of its bulky and elaborate piers resulted in the tides upstream returning to the rapid flows as they were downstream and before its forming of a near-barrier. That bridge was particularly dam-like when it housed 200 buildings in the Tudor period and in depictions at the time of the Great Fire of London which spared the bridge. This change, together with dredging of the lower river (lowest reaches) and construction of Teddington Lock and weir, meant that for hours of each day the Thames at Richmond, Twickenham, Ham, Petersham and northern Teddington, was a shallow watercourse running past great mud and shingle banks. The exception was after weeks of above-average rainfall when the river is known as in spate however such outflow hinders navigation upstream. By the late 19th century water extraction above Teddington had increased to four of five of the city's main waterworks and after light or normal rainfall more barges found it impossible to navigate the reach during and for hours around the two low tides each day. In 1890, after many years of petitioning, an Act of Parliament was enacted to build the half-lock and weir, the Richmond Footbridge, Sluice, Lock and Slipway Act 1890. This is among a small minority of Thames locks not to have been built around an island or islands (aits). Details of design A barge lock was constructed against the north-east ("Surrey") side. This is followed by four immense brick piers protected by large ashlar stone cutwaters (starlings). These in turn support relatively thin stone dressings reaching to the metal parapet level, carved in a classical style with reredos and cornices, supporting painted metal arches. A matching-colour balustrade is above the arches finished with black lanterns, metal pillars and simple finials. The piers house the barriers and the arches support a pair of horizontal decks (walkways). Against the opposite bank is a gently elevated slipway accessed from upstream and downstream parts of the river. As a superstructure was required to hold the suspended barriers, authorities agreed to build this in the form of