Understanding Riparian Ownership and Flood Risk

If your property has a watercourse running through or alongside your property grounds, you may have a legal obligation to maintain it.

This legal responsibility for managing a watercourse running through or alongside your property grounds is known as Riparian Ownership.

In this blog, we aim to inform you as to what Riparian Ownership means, what your responsibilities as a Riparian Owner may include, and how these responsibilities tie in with the Environment Agency (EA) and Lead Local Flood Authority (LLFA).

What is a Riparian Owner?

A Riparian Owner is someone who has a watercourse that runs through, next to or beneath their property grounds. This could include:

• A stream that flows directly through the property grounds.
• A stream that flows along a boundary section of the property.
• A ditch or drainage channel which runs directly through the property grounds or forms part of the property boundary.
• A culverted watercourse flowing beneath or on the surface (a watercourse enclosed within a pipe or tunnel).

When are Landowners Responsible for a Watercourse?

If you have a watercourse which flows directly through your property grounds, which has land under your ownership on both banks of the watercourse, then you are fully responsible for maintaining the whole section of the watercourse which flows through your property.

If you have a watercourse that forms part of a boundary to your property grounds, then you are responsible for maintaining up to the centre line of the watercourse. The centre line refers to the riverbed and banks up to the middle section of the watercourse. The adjacent land/property owner is equally responsible for maintaining their side of the watercourse up to the centre line. This is generally considered the case, unless another third party is known to hold ownership. This should be outlined within your property deeds if this is the case.

If you have a culverted watercourse that runs beneath your property, then again, you are responsible for maintaining the full section of the culverted watercourse running beneath your property. This responsibility falls under the Land Drainage Act of 1991, whereby landowners have a legal duty to ensure any culverted system beneath their land is well maintained to promote the free flow of water through the system. Many property owners are unaware if they have a culverted watercourse flowing beneath their property grounds, so it is worth checking your property deeds with the Land Registry.

Watercourses are not static in their nature; they can gradually shift overtime due to the effects of erosion and sediment deposition. Consequently, when a watercourse changes with time, the legal responsibility and Riparian Ownership will also change with it. This is a principle referred to as the ‘doctrine of accretion and diluvion’, which acknowledges that the land adjacent to a watercourse may expand or recede with time, brought on by the natural processes of rivers.

The HM Land Registry as of March 2020 states:

“The doctrine of accretion and diluvion recognises the fact that where land is bounded by water, the forces of nature are likely to cause changes in the boundary between the land and the water. We would expect these changes to be gradual and imperceptible. As the watercourse changes naturally and progressively with time, so the land boundary follows it. There may be some gain, there may be some loss. The law accepts this and considers it to be fair.

If a powerful flood wrenches the watercourse suddenly but permanently into a different direction so that a substantial and recognisable change in the boundary has taken place, then the doctrine of accretion does not apply. Neither does it apply if the changes are man-made”.

The illustrated diagram below is an example of typical circumstances where you are the riparian owner:

Property A is a Riparian Owner.

Property A is responsible for the culvert running beneath the southern property grounds and also up to the centre line of the watercourse situated to the west of the property boundary.

Property B is a Riparian Owner.

Property B is responsible for their section of the culvert running beneath the southern property grounds.

Property C is a Riparian Owner.

Property C is responsible for the watercourse to the North of the property boundary, extending to the central line.

Property D is a Riparian Owner.

Property D is responsible for the watercourse to the North of the property boundary, extending to the central line; And is also responsible for the whole section of watercourse which runs through the western section of the property grounds.

Property E is not a Riparian Owner.

As the property boundary does not extend to the watercourse.

Noticeable features such as hedges, fences and watercourses may not define the legal boundaries of a property. It is therefore very important to check property deeds and seek legal advice as necessary.

What are the Responsibilities of Riparian Owners?

If any of the above scenarios apply to your property, then you will likely have the following responsibilities as the Riparian Owner:

• You will need to maintain the bed and banks of the watercourse. This includes repairing any damage to the riverbanks caused by turbulent river flows and preventing erosion of the river banks.
• Ensure the free flow of water within the watercourse. It is your responsibility to remove any debris or vegetation which may impede the free flow of water.
• Pollution Management. Ensuring that no harmful pollutants enter the watercourse is a key environmental responsibility of any Riparian Owner. Environmental pollutants include grass cuttings, building/construction waste and chemicals.
• Water Displacement. As a Riparian Owner you are not allowed to dam, divert, or block the watercourse in anyway that affects areas downstream or upstream. The natural free flow of water should be allowed at all time.
• Allowing free passage for fish and other waterborne wildlife.
• Structural Maintenance. If a culvert runs beneath your property, you are responsible for keeping it free of debris and structurally sound.

What is the Role of the Environment Agency?

The Environment Agency has some responsibility to maintain or undertake works on Main Rivers.

However, the EA are not obligated to maintain or undertake work on Main Rivers by any legal law or legislation. The EA will only undertake their non mandatory responsibility for managing Main Rivers when it is deemed as a cost-effective way to reduce potential flood risk and protect the environment. This passive level of responsibility also applies to the LLFA’s and IDB’s (Internal Drainage Board’s who usually look after Ordinary Watercourses).

If a Main River or Ordinary Watercourse runs through your property grounds, it is your responsibility as the Riparian Owner to maintain your section.

When do you need a Permit?

In order to undertake certain maintenance procedures on a Main River, you may need to obtain a Flood Risk Activity Permit (FRAP) (also known as Environmental Permits) from the EA.

Any maintenance works that are planned to take place on a Main River that have the potential to disrupt the flow of the river or the surrounding environment will need a FRAP. Such works include:

• Preventing or repairing bank erosion.
• Constructing or altering structures, such as walls, culverts, or outfalls.
• Removing or depositing materials like silt, sand, or gravel from the riverbed.

You will also require a FRAP depending on the location of the maintenance works you plan to undertake, such as:

• If maintenance works are taking place within the river channel itself, or within 8 metres of the bank of a Main River.
• Within the river channel or within 16 metres of a tidal Main River.
• Within the floodplain of a Main River. The floodplain is categorised as Flood Zone 3 or Flood Zone 2.

What About Ordinary Watercourses?

You are exempt from requiring a FRAP if you are undertaking maintenance works in an Ordinary Watercourse. However, you may still require land drainage consent from either the LLFA or IDB if the works could affect water flow or flood risk.

Summary:

If a watercourse runs through or alongside your property, take the time to check your deeds and seek legal advice as necessary.

Understanding and fulfilling your legal responsibilities is vital to protecting your property and neighbours, as well as the wider environment from unnecessary flood risk.

If you have any queries regarding riparian ownership responsibilities for a watercourse at your property or in your local area, please get in touch with FPS Environmental who can readily assist with our surveyors and consultants, who have in depth legislation knowledge regarding watercourses and flood risk.

18th July 2025

Written by: Reece Hewitt MSc BSc (Hons) MCIWEM – Senior Flood Risk Consultant