Controlling the effects of water on public rights of way is one of the most important aspects of maintenance work.
Although the amount of annual rainfall is extremely variable across England and Wales, in all regions there is sufficient rainfall to ensure there will be problems unless the paths have good natural drainage or have drains constructed to carry water away. Drainage work on rights of way is undertaken by the highway authority as part of its statutory duty to maintain the PROW network, or by exercising its power to improve highways for the enjoyment of the public. Whether or not the highway authority has a statutory duty to carry out drainage works will depend on the circumstances of the case in question. The primary responsibility for drainage normally rests with the landowner, but the authority may have acquired that responsibility at any particular location by having carried out that work previously. Alternatively, the work may involve the repair of works already carried out by the authority itself rather than by the landowner. It should always be remembered that when the highway authority chooses to improve the drainage of a path by constructing new drains or culverts, it will acquire the future maintenance responsibility for those structures.
Preliminary Considerations for Drainage Work
The first consideration is whether drainage is actually the best option to deal with a water problem. A simpler solution for a muddy path may be to cut back shading vegetation to allow in light and wind, which may be sufficient to dry out the path. Establishing a grass surface can also help dry a surface by transpiration. Where water is pooling on a compacted path, it may be sufficient simply to raise the level by adding free-draining graded stone. On very wet sites, such as peat bogs and marshes, drainage may be impractical or undesirable for reasons of nature conservation and would be illegal on a SSSI site unless approved by English Nature (EN) or the Countryside Council for Wales (CCW).
In such cases boardwalks or large stone flags can be considered for short lengths. For longer lengths a ‘floating’ path on a raft of fine grade geotextile, also with geogrid if the path is to receive heavy traffic, is a good option. A further option is maybe to divert the path onto a drier route. In some cases intercepting water that is flowing onto the path at a point higher up (e.g. from a road) will be much simpler than draining a path.
The next consideration is ensuring that the watercourse that the new drain will feed into has sufficient capacity to cope with the extra water. The local drainage board or Environment Agency should be consulted, but no consents or fees are mandatory for work relating to ordinary watercourses (not main rivers) when Highway Authorities are carrying out work under their legal powers and duties.
A path’s construction has a bearing on whether drainage is needed, and if so the type of drain required. The most basic type of path, into which category the vast majority fall, has no construction as such but consists of earth flattened and compressed by use, often with a grass component. Paths of this type over relatively flat terrain on well-drained soil (mainly sand or chalk rather than clay) should need no drainage at all. However, even on well-drained soils, paths that slope or are adjacent to sloping terrain will usually require drainage to deal with a build-up of surface water. This is more pronounced on soils with a high clay content, as water does not easily penetrate these, and much tends to run straight off. It is the build-up of surface water that damages paths.
With constructed paths, if the surface is impermeable, such as concrete or tarmac, no water will be absorbed and all of it falling or flowing onto the path will have to be collected or allowed to run off onto the adjacent land. Stone-pitched paths will shed some water but much will percolate through the gaps - so the base needs to be free-draining. A path surface of rolled stone dust will absorb some water, but if it is well-compacted and subjected only to low flows it should retain most of its structure and allow water to flow away. Such a surface should cope quite well with the rain falling on it provided it is cambered or has a cross-fall, but it will not cope with any build-up of water that results in significant concentrated flow across the surface. Cross-drains consisting of stone-filled gullies, or gullies covered by grills can help take away surface water in high rainfall areas to help with this. With porous surfaces a base of graded stone (no fines) helps to allow water to permeate through the path into the subsoil. On clay or peat soils fines tend to rise to the surface and the path material effectively sinks. To avoid this the graded stone base should be laid on fine-grade geotextile to act as a filtration barrier and prevent fines rising. Surfaces of loose stones or chippings will obviously allow a lot of water through, but even these can be subject to erosion if surface flows build up beyond a certain level - usually on sloping paths or where water is allowed to flow from adjacent slopes.
Types of Drain
The most basic and common type of drain is an open ditch. These are perfectly adequate for most situations, and in some areas are a major wildlife habitat. However, they are potentially dangerous for children, need regular clearing and may take up too much width on narrow paths. For the latter, such as hollow-ways, or where open drains would be likely soon to fill in with leaves etc, French (stone-filled) drains are a good option. These historically consisted of ditches filled with graded stone, allowing water to flow between the stones to an outlet point. Nowadays it is normal practice to bury a plastic drainage pipe in the bottom of the trench, the pipe being porous on its upper side and allowing water to trickle in and flow quickly along the bottom of the pipe. Another option to French drains is to cover the ditch with concrete or stone slabs, but this would be tend to be used only on formal paths.
A distinction can be drawn between drains that take in water along their length, and those that simply transport away from a site to an outlet point. The latter tend to use covered pipes, historically ceramic, then steel, then concrete, and now almost always plastic.
A further type of ‘drain’ is the cut-off - a line of stone setts or an embedded piece of timber that deflects water off the path. This is a simple, rather crude method, but is appropriate where ‘proper’ drainage is not feasible for whatever reason. A more sophisticated version uses French drains across the path, or channels covered by grills.
Construction of New Drains
Basic considerations when constructing new drains:
- Wherever possible water should be intercepted before it gets onto a path, i.e. on the upper side. If drainage is deemed necessary it should be implemented before any path surfacing work is undertaken, as this could otherwise easily be undone by erosion. When excavating a new drain, or indeed clearing an existing one, unless the ground is very dry, work should start at the lowest point and move upslope. This allows water to flow away, since if work is started high up, water tends to pool in the excavation and hinder work.
- In sensitive locations such as National Parks, pipes of man-made materials can look intrusive, so stone slab culverts should be considered. If man-made pipes are used the ends should not visible but hidden from view with stone slabs. Stone infill for French drains should be locally sourced. In locations prone to vandalism the ends of small gauge plastic pipes are vulnerable and should be protected by concrete.
Maintenance of Drains
The frequency of the need for maintenance depends on a number of factors. With open drains, if they are accessible by stock, the side walls will be subject to damage by poaching. Open drains beside hedgerows or under trees will also tend to fill up with leaf-litter, unless they are fast flowing. Those with low water levels will tend to scrub up fairly quickly. Invasive introduced species can be a problem, including those growing on the banks such as Himalayan Balsam, Giant Hogweed and Japanese Knotweed which require careful treatment with glyphosate. Also emergents, such as Great Reedmace and aquatics such as Canadian Pondweed which require repeated pulling out, will also need attention.
Any drain taking water with a high silt content, such as washings from a quarry or run-off from an opencast site, will tend to silt up rapidly. When clearing open drains, nature conservation should be considered and times when aquatic life is active or vulnerable should be avoided. The stones in French drains become silted over time and need to be dug out, cleaned and replaced. The need for this should be greatly reduced by including a plastic drainage pipe. Buried pipes can be damaged by over-running of heavy traffic, necessitating replacement. This can generally be avoided by using a pipe of appropriate strength and placing sufficient fill above it to dissipate the load.
Developing a Drainage Works Programme
The Authority should develop a drainage works program to include:
- Construction of new drains in order to improve the condition of paths: the construction of new drains may be considered necessary by the highway authority for the following reasons.
- Paths which are included in an improvement programme which is aimed at providing a better surface or drainage in order to encourage more people to use them.
- Paths where the level and type of usage has changed leading to public requests for better surface or drainage. For example, paths on the edge of urban areas may become more used by elderly or disabled people and it is desirable to improve the path accordingly.
- Occasionally it may be necessary to construct new drains because the original drains can no longer cope with the flow. Such instances need to be investigated fully because it may be due to a land drainage problem which is the responsibility of the landowner rather than the highway authority. However, the problem may be due to higher surface water run off or higher water table primarily due to wetter milder winters of recent years.
Maintenance of existing drains which are the responsibility of the authority: as with other forms of maintenance work, drainage work tends to be cyclical in nature. Typically, there will be a proportion of the path network which requires regular ditch clearance etc., and a routine inspection regime should have been established. In practice, this may not be the case due to lack of staff resources, and if that is so, it should be rectified as soon as possible. In the absence of a regular maintenance schedule, it is worth checking any records which may exist relating to a particular path before carrying out any drainage work. This is necessary in order to ensure that the duty to maintain the drains has been acquired by the authority. As a general rule, any drains alongside a path and outside any boundary fence are likely to be the responsibility of the authority. Similarly, any drains which cross the path are also likely to be the responsibility of the highway authority. If in any doubt, the land drainage section should be consulted.
In addition to routine clearance work, maintenance will also involve the repair of existing drains where this has become necessary. The need to carry out repair work will become apparent through complaints received or because of routine inspections, and these need to be incorporated into the annual maintenance programme.
Local authorities have two general areas of responsibility; as drainage bodies and as highway authorities.
As drainage bodies, they have powers under the Land Drainage Act 1991 to carry out drainage schemes and to execute works for the prevention of flooding. Although some of the powers under this Act are relevant to PROW, they should not be exercised without the advice of the local authority land drainage officers. Highway Authorities have duties and powers to ensure that highways are properly drained, and are not adversely affected by drainage of adjacent land.
Broadly speaking therefore there are two categories of drain; land drains and highway drains:
- Land Drains — are primarily the responsibility of the landowner, but the highway authority has powers to ensure that the operation of such drains does not adversely affect any highway.
- Highway Drains — despite their name are not necessarily the responsibility of the Highway Authority. The High Court has considered whether or not a ditch lying between the highway and neighbouring land forms part of the highway. In Hardcombe v Bedfordshire County Council (1938) it was affirmed that the ditch does not form part of the highway itself because it is not used by the public in order to exercise the right of passage. It appears that the maintenance of drains alongside PROW is the responsibility of the landowner. However, where a Highway Authority, as a matter of expediency, has carried out maintenance work on such drains it will have acquired that responsibility. If the Highway Authority has created a new ditch alongside the highway, or a culvert underneath it the maintenance of these facilities would clearly be the responsibility of that authority.
Local authorities have the powers to drain highways under common law and the following Acts of Parliament.
Under Common Law it is the duty of the owner of land adjoining a highway to ‘cleanse and scour his own ditches to such an extent as to prevent nuisance and obstruction to passengers’ (A- G v Waring (1899) 63JP789). Any flooding of the highway caused by a failure on the part of the landowner to carry out such routine maintenance constitutes a public nuisance for which he may be prosecuted (on indictment) or an injunction sought to restrain him from further neglecting to cleanse the ditch.
Land Drainage Act 1991
Section 20 Power to carry out drainage works
Section 20(2) provides that a local authority other than the council of a non-metropolitan district may, by agreement with any person and at that person’s expense, carry out within the local authority’s area any drainage works which that person is entitled to carry out.
Section 23 Consent for erecting any culvert
Section 23(1)(b) provides that ‘No person shall erect any culvert that would be likely to affect the flow of any ordinary watercourse or alter any culvert in a manner that would be likely to affect such a flow, without the consent of the drainage board concerned’. Sub-section (2) enables the drainage board to charge a fee for applications for consent, but section 6(b) exempts Highway Authorities from this legislation when carrying out works under their statutory duties or powers.
‘Watercourse’ is defined as including ‘all rivers and streams and all ditches, drains, cuts, culverts, dykes, sluices, sewers [other than public sewers within the meaning of the Water Industry Act 1991] and passages through which water flows, and ‘ordinary watercourse’ means a watercourse that does not form part of a main river.
Section 25 Power to require landowner to carry out works
This section provides the Highway Authority, or the Environment Agency, with a power to require a landowner to carry out works to maintain the flow of water in 'ordinary' watercourses, i.e. those that do not form part of a 'main' river. The Environment Agency must be consulted before these powers are used, and the Agency is also the body to advise on whether or not a particular watercourse meets the description of 'ordinary'. PROW managers do not normally use these powers without involving the local authority land drainage officers.
Highways Act 1980
Section 100 Power for highway authorities to carry out works
This section of the Act provides the Highway Authority with the power to carry out works to drain the highway, or to prevent water from flowing onto it. Specifically, this section allows the Highway Authority to do the following:
- Construct or lay drains in the highway itself, on land adjacent to it, or on land near to the highway.
- Construct barriers on the highway or on adjacent land in order to divert water into existing drains.
The water diverted or directed by the above works can be discharged into any inland waters, either natural or artificial, or any tidal waters.
As a matter of good practice, the Highway Authority should serve a notice of intent on the relevant landowners if it intends to carry out works on any land adjacent to the highway. If the landowners concerned consider that the works have damaged that land, the Highway Authority is liable to pay compensation under the provisions of Section 100, subsection (3).
The Highway Authority can take action against any person who interferes with any drain or barrier constructed under the above powers. Under these circumstances, the Authority can carry out restoration works and recover the cost of doing so from these persons responsible. Those persons are also guilty of an offence and are liable for a fine not exceeding three times the cost of the works.
When the Highway Authority intends to lay drains in the highway itself, there is no requirement to consult the landowners because the surface of the highway is vested in the authority by virtue of Section 263 of the Highways Act 1980. If the new drains connect to an existing drainage system and do not alter the drainage pattern on adjacent land, then as a general rule consultation is unnecessary. However, if the new drains alter the drainage pattern on adjacent land, then clearly it would be necessary to consult the relevant landowners in advance.
Where a highway is privately maintainable, the persons responsible for its maintenance have similar powers to the Highway Authority under this section of the Act.
Section 101 Power for highway authorities to deal with ditches which may be a danger to the public
This section of the Highways Act 1980 provides the Highway Authority with additional powers to deal with ditches on land near to the highway which are regarded as a danger to the public. Under this section, the Highway Authority may do the following:
- Fill in any such ditch which is considered unnecessary for drainage purposes, provided that the landowners agree, in writing that the ditch is unnecessary.</li
- Alternatively, lay pipes in the ditch before filling it in and, if necessary this can be done without the consent of the landowner, although the consent of the Environment Agency may be required.
If the landowner considers the land has been damaged by any of these operations, the Highway Authority is liable to pay compensation.
If the landowner reopens any of the ditches treated under the above powers, the Highway Authority may close them again and recover the cost from the landowner. The landowner is also guilty of an offence in these circumstances and is liable for a fine of up to three times the cost of the works.
The Highway Authority cannot exercise its powers under this section in respect of land used for operating railways or canals unless:
- 14 days notice of the works to be carried out is given to the rail or canal undertakers.
- Any reasonable requirements of those undertakers are taken into account. If there is any disagreement as to whether the requirements are reasonable, the matter has to be referred to the Minister in England or the National Assembly in Wales.
Section 102 Power to provide barriers to protect against natural hazards
Under this section, the Highway Authority may provide barriers or other works to protect the highway from snow, flood, landslide or other hazards of nature. Compensation is payable to any landowner who considers that the land has suffered as a consequence of the work being undertaken.
There are also specific powers under the following sections of the Act which allow the Highway Authority to divert or carry out works on watercourses which are not necessarily adjacent to the Highway. As a matter of good practice, these should not be used before seeking the advice of the local authority drainage engineers, who will seek the consent of the Environment Agency in appropriate cases.
Sections 108 and 109 Power to divert navigable watercourses
These sections provide the Highway Authority with a power to divert navigable watercourses for purposes of highway maintenance or improvement. They would require the consent of the Environment Agency and are not likely to be used by PROW managers.
Section 110 Power to divert non-navigable watercourses
This section allows the Highway Authority to divert any non-navigable watercourse or carry out works to any watercourse, if these measures are necessary for the construction, improvement or alteration of a highway. The section contains provisions which deal with serving notices on landowners, dealing with objections and compensation. These powers require the consent of the Environment Agency and are not normally required to be used in connection with PROW maintenance.
Section 151 Prevention of soil being washed onto street
Under this section, the Highway Authority can serve a notice on a landowner requiring works to be carried out in order to prevent soil or refuse being washed onto the highway, or into any sewer or gully.The landowner can appeal against the notice in the Magistrates Court.
This section provides an alternative to Section 102 which provides the Highway Authority with the power to carry out such works itself, and which power to use will depend on the circumstances of each case. The factors which have to be evaluated are:
- The scale and likely cost of the works if the Highway Authority decides to do the work itself.
- The possible cost of compensation payable to the landowner if that person considers that the land has been damaged.
- If the notice is served under Section 151, the legal costs of contesting an appeal by the landowner in the Magistrates Court.
The advice of the Highway Authority Legal Officers should be sought before any decision is taken.
Section 163 Prevention of water falling on or flowing on to highways
This section provides the Highway authority with the power to require a landowner to construct or maintain any channel, gutter or downpipe in order to:
- a) prevent water from falling onto persons using the highway.
- b) prevent water from flowing across a footway from adjoining premises.
These powers are primarily used in urban areas, and clearly those in (b) apply only to footways rather than PROW. Since some routes recorded on Definitive Maps are located within urban or semi-urban areas, it is possible the powers in (a) may occasionally be used by PROW managers.
Public Health Act 1936
The Highway Authority may also exercise any powers exercisable by a water authority under the Public Health Act for the purpose of draining a highway in its area. Before exercising those powers, the Highway Authority has to consult the Environment Agency and any district council that may exist.
These powers are not normally required to be used in connection with PROW maintenance, and are the responsibility of the local authority's Environment Health Department.
Glossary of Terms
Cut-off drains are used to intercept water and direct it into adjacent drains. Typically on PROW they are used to direct water off the surface of the path into drains alongside it. They often take the form of a line of stones set at an angle across the path standing slightly proud of the surface, and this directs the water into the drain. They may also be constructed out of timber.
The most common and simplest means of carrying water is a ditch alongside the path or adjacent land. Ditches require regular maintenance which includes the removal of vegetation or other material impeding flow, and removal of accumulated silt which can eventually block the drain.
A term used to describe a very small ditch required to carry small quantities of water across the path or alongside it.
Constructed out of concrete, steel or wood, these provide a stronger and more durable means of carrying water than an unlined ditch. They are commonly constructed out of concrete sections sometimes in the form of a half diameter pipe. In upland areas, small channels which cross a path linking drainage ditches on either side of the path are often lined with stone and sometimes wood. In urban areas drainage channels are often constructed out of steel with perforated covers flush with the surface of the path. Drainage channels carry water more quickly and more effectively than an unlined ditch, but they are more expensive to construct and repair.
French drains are drainage ditches filled with clean aggregate which allow water to pass below the surface of the ground. They have a much lower carrying capacity than an open ditch, and cannot be used where vigorous flows are anticipated. They are very useful when space alongside the path is limited and an open ditch is not necessary to accommodate the flow. Flow capacity is sometimes increased by laying steel reinforced plastic perforated pipe in the base of the french drain.
Culverts provide a means of carrying water beneath the surface of the path and are constructed by means of pipes or box sections. The size of the culvert is crucial in ensuring that peak flows can be accommodated, and a knowledge of local conditions is essential at the outset. Drainage pipes are the commonest form of culvert and may be constructed out of concrete, clay, steel or plastic. The type of traffic using the path has to be taken into account when deciding which type of pipe to use at any particular location. Where vehicular traffic is involved, the use of concrete, clay or steel pipes will be necessary. Plastic pipes are easy to transport to site and can also be very durable when strengthened by metal loops. Pipes are laid on an aggregate base, and where flows are expected to be vigorous, a headwall is constructed at the inlet and outlet of the culvert. Headwalls are constructed out of concrete block, brick and sometimes stone, and they prevent the ends of the culvert from being eroded by directing the flow of water. Box culverts can be made out of stone, concrete or, less commonly, wood.
In many upland areas stone box culverts are common since local stone can be used in situations where access is difficult. Wooden culverts can also be used in remote areas where they can be assembled on site, but they are usually used only for small flows and where traffic is expected to be light.
Crossfall and Camber
Whilst these terms are applied to the profile of a path surface, their purpose is to ensure that the path is properly drained. The term 'crossfall' is used when the surface of the path slopes to one side thus directing the flow of water in that direction. The tem 'camber' is used when the surface of the path is higher in the centre than on the sides, thus directing water to both sides of the path.
The term gulley can be used to describe a ditch or drainage channel. 'Gulleying', however is a term used to describe damage to the surface of the ground caused by uncontrolled water run-off. If not rectified, gulleying can destroy the surface of a path and quickly cause it to become 'out of repair'.
This is a pit filled with clean aggregate which stores water which eventually seeps away into the ground. Soakaways are used when it is not possible for drains to connect with the surrounding drainage system, and when there is sufficient land available to dig a large enough soakaway.
'Land Drainage and Flood Defence Responsibilities - A Practical Guide' by The Institute of Civil Engineers Published by Thomas Telford.
'Footpaths - A Practical Handbook' British Trust for Conservation Volunteers (BTCV).
'Making the Best of Byways' DEFRA