Watercourses

Any existing drainage features like open watercourses and pipes (culverts) should be identified, investigated and considered early in the design process as these often have legal easements which cannot be built within.

Consent may be required in order to make any alterations to them, or to carry out works that may impact flows or easements.

A watercourse is defined in the Land Drainage Act 1991 as 'all rivers and streams, all ditches, drains, cuts, culverts, dikes, sluices, sewers (other than public sewers within the meaning of the Water Industry Act 1991) and passages, through which water flows'.

You will need to establish if a watercourse is defined as a 'main river', or as an 'ordinary watercourse'. If it is an ordinary watercourse, you will also need to check if it falls within an area managed by an 'Internal Drainage Board'. This will impact what consents will be required and easement widths.

'Main Rivers' are shown on a statutory plan, a copy of which is held at the local Environment Agency office at Guildbourne House, Chatsworth Road, Worthing, West Sussex BN11 1LD.

'Ordinary watercourses' are defined but not specifically identified on a statutory plan. In practice, they may range from a reasonable sized ditch with a constant flow to nothing more than a depression which carries water infrequently. Whilst these watercourses may now take surface water runoff from highways, roofs and hardstanding, the original base flow will be from a land drainage source (for example groundwater and runoff from undeveloped land).

Easements

Easements to watercourses, whether they are open or culverted, are often required by authorities. These easements are necessary to ensure that future access for maintenance is not restricted.

In practice this means that if you wish to carry out works within an easement you will need consent from the relevant authority.

Typical minimum easements for different watercourses include:

  • 8 metres from a main river,  
  • 16 metres from a tidal main river,
  • 8 metres from an Internal Drainage Board watercourse,
  • 3m from an ordinary watercourse in the Arun district.

Where a watercourse is open the easement applies from the top of the nearest bank.

Where a watercourse is culverted, the same easement applies to the nearest edge of the culvert.

Works to watercourses

Culverting (piping) a watercourse is not advised unless there is no alternative. The resulting reduction in storage volume, flow capacity and habitat potential would be unacceptable. Culverted watercourses are also more difficult and costly to maintain due to the limited accessibility.

Consents

For works on or near a Main River, an Internal Drainage District watercourse or flood defence, you will need consent (in the form of a Flood Risk Activity Permit) from the Environment Agency.

Land Drainage Consent must be sought from the Lead Local Flood Authority (West Sussex County Council) prior to starting any temporary or permanent works that affect the flow of water in an ordinary watercourse. Such works may include culverting, channel diversion, bank reinforcement, connections, headwalls and the installation of trash screens.

Please also refer to the 'culvert policy' and consent application form available on the West Sussex County Council (WSCC) website.

Please note that we no longer undertake Land Drainage consenting on behalf of WSCC.

Any works which do not need Land Drainage Consent may require our consent as stipulated by our Land Drainage Byelaws. Applicants are invited to contact us at land.drainage@arun.gov.uk to find out if Land Drainage Byelaw Consent is required.

Page last updated

26 November 2025