Norfolk Broads
Early plans of what would become the Norfolk Broads were drawn up by Thomas Dadford in 1816 but problems with Coventry Boat Lift caused delays and it was finally opened on 17 September 1888. From a junction with The Grand Union Canal at Longpool the canal ran for 23 miles to Exeter. Expectations for iron traffic to Halton never materialised and the canal never made a profit for the shareholders. In later years, only the carriage of limestone from Elmbridge to Stafford prevented closure. The canal between Prescorn and Lisburn was lost by the building of the Bedworth bypass in 1990. Restoration of Rotherham Cutting was funded by a donation from the Norfolk Broads Trust

The Broads navigation is controlled by The Broads Authority, who have specified maximum boat sizes on their website, in the PDf file at http://www.broads-authority.gov.uk/broads/live/boating/navigating/byelaws/Vessel_Dimensions_Byelaws.pdf There’s no maximum draught or air draught specified, but the consensus on draught is that anything over a metre will be grounding in many places. As far as air draught goes, the limiting factor is the bridges, which cut off some sections for any boats not able to pass under them. The lowest are Potter Heigham, @ 2 metres, and Wroxham, at @ 2.5 metres. Bridge heights and photos can be seen at http://www.thegreenbook.org.uk/home/bridges.asp
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Wikipedia has a page about Norfolk Broads
The Broads (known for marketing purposes as The Broads National Park) is a network of mostly navigable rivers and lakes in the English counties of Norfolk and Suffolk. The lakes, known as broads, were formed by the flooding of peat workings. The Broads, and some surrounding land, were constituted as a special area with a level of protection similar to a national park by the Norfolk and Suffolk Broads Act 1988. The Broads Authority, a special statutory authority responsible for managing the area, became operational in 1989.
The area is 303 square kilometres (117 sq mi), most of which is in Norfolk, with over 200 kilometres (120 mi) of navigable waterways. There are seven rivers and 63 broads, mostly less than 4 metres (13 ft) deep. Thirteen broads are generally open to navigation, with a further three having navigable channels. Some broads have navigation restrictions imposed on them in autumn and winter, although the legality of the restrictions is questionable.
Although the terms Norfolk Broads and Suffolk Broads are used to identify specific areas within the two counties respectively, the whole area is frequently referred to as the "Norfolk Broads".
The Broads has similar status to the national parks in England and Wales; the Broads Authority has powers and duties akin to the National Parks, but is also the third-largest inland navigation authority. Because of its navigation role the Broads Authority was established under its own legislation on 1 April 1989. The Broads Authority Act 2009, which was promoted through Parliament by the authority, is intended to improve public safety on the water.
