Last edited 10 Feb 2022

Main river

A main river is: ‘A watercourse in England or Wales shown as a main river on a map prepared by the Environment Agency or Natural Resources Wales under the Water Resources Act 1991. The main river designation includes the watercourse, its banks and any connected drainage works. In England the Environment Agency has permissive powers to carry out flood defence works on main rivers but responsibility for maintenance remains with the riparian owner. Natural Resources Wales has the same permissive powers in Wales. Watercourses not designated as main river are known as ordinary watercourses.’ Ref Culvert, screen and outfall manual, (CIRIA C786) published by CIRIA in 2019.

NB Water Bill, Glossary: water terms, published by the Department for Environment, Food and Rural Affairs in November 2013, defines a main river as: ‘A watercourse shown as such on a main river map. All other watercourses are defined as “ordinary watercourses”. The Environment Agency has flood risk management responsibility for main rivers in England and Natural Resources Wales has flood risk management responsibility for main rivers in Wales. Ordinary watercourses are the responsibility of Internal Drainage Boards where they are located within internal drainage districts and the responsibility of the Lead Local Flood Authority where they are outside of a drainage district.’

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