You will need consent from the Middle Level Commissioners or the local IDB before any works in the channel, e.g. culverting or filling, are carried out, whether the watercourse is private or a District Drain.
If the watercourse is a District Drain, any work within the statutory byelaw distance requires the specific consent of the Commissioners or the IDB. The byelaw distances are 20 metres (66 feet) for a Middle Level watercourse and 9 metres (30 feet) for an IDB District Drain. You will also need consent to discharge an increased rate or volume of flow to a watercourse, for which a charge, based on the cost of dealing with such extra rate or volume, is levied. The monies so raised are used to help pay for the extra maintenance or capital works required as a result of such development.
Do not forget that other consents, such as planning permission, Environment Agency consent, e.g. for impounding structures, and water quality and local authority consent for culverting, may also be required.
The link below opens a pdf document, provided by the Environment Agency, outlining the rights and responsibilities of those who own land or property next to a watercourse.
Living on the Edge