The River Medlock makes an end-on connection with the Bridgewater Canal at Knott Mill Bridge. Originally surplus water was diverted, via a tippler weir, into an overflow tunnel passing under the basin and emerging just to the north of the overspill from the Giant's Basin. The tippler weir has been replaced with a conventional weir within the basin. The 1848 OS large scale map shows the original course as following the line of the canal as far as the coal wharf (site of the Giant's Basin). The River Irwell forms two gigantic meanders around Manchester and Salford; these too have had to be heavily controlled, for the Irwell was straightened and deepened from 1724, forming the Mersey and Irwell Navigation with quays built along Water Street in 1740. Most of the navigation was abandoned in the 1890s, with the construction of the Manchester Ship Canal but a deep water channel was maintained up to the Woden Street footbridge. Two canals define Castlefield: the Bridgewater built in 1761 and the Rochdale opened in 1804. There are however two more short canals within Castlefield that form links with the Irwell, these are the Manchester and Salford Junction Canal and the Hulme Locks Branch Canal, both being disused but both are still visible. The Bridgewater Hall basin on the former has been restored. Over the Irwell from Water Street is the entrance to the Manchester, Bolton & Bury Canal.