- Project plans
- Project activities
- Legislation and standards
- Industry context
Last edited 27 Aug 2018
The construction of roads affects the natural surface and subsurface drainage pattern of watersheds or hill-slopes. The provision of adequate drainage is important to prevent the accumulation of excess water or moisture on or within road constructions that can adversely affect their material properties, compromise overall stability and affect driver safety. Drainage must cope with water from the carriageways, hard shoulders, foot/cycle paths, verges, and adjacent catchment areas.
The design of highway drainage will depend on several factors, including:
- The intensity of rainfall expected.
- The size of catchment area.
- The permeability of the surfaces.
The road camber or cross-fall should be designed to cope with heavy water run-off. Insufficient cross-fall can increase the risk of vehicles skidding or aquaplaning on the surface water. The standard cross-fall for roads is usually taken as 1:40, although the camber will vary depending on the individual requirements of the road.
Surface water is generally collected in channels at the road-side and discharged through gullies (drainage gratings at the edges of the road) into storm water sewers. Gullies are typically positioned at intervals of 25-30 m, depending on the road width and nature of the cross-fall. Gully covers can be either top opening or side opening.
To reduce the number of required drainage points, pavings and verges should be graded towards the channel.
For more information, see Culvert.
Minor roads usually use simple openings or channels which feed into roadside ditches.
Most main roads use a system of gullies and piped sewers. However, soakaways may also be used to discharge water, these are large underground chambers into which water flows from a gully. Water collects and gradually soaks through holes into the surrounding ground or to streams and roadside ditches.
For more information, see Soakaway.
For roads with hard shoulders, it is usual for the kerb to be kept flush with the road surface, with a precast concrete channel placed at the outside edge to drain water. This channel discharges water into gullies.
 Find out more
 Related articles on Designing Buildings Wiki:
- Bituminous mixing and laying plant.
- Catchment flood management plans.
- Code of Practice for Ironwork Systems Installation and Refurbishment.
- Highway engineers and drainage.
- Overview of the road development process.
- Planning for floods.
- Pumps and dewatering equipment.
- Road construction.
- Road improvement scheme consultation.
- Road joints.
- Runway construction.
- Section 50 agreement.
- Sewer construction.
- Sustainable urban drainage systems SUDS.
- Types of road and street.
- Water engineering.
 External references
- ‘Introduction to civil engineering construction’ (3rd ed.), HOLMES, R., The College of Estate Management (1995)
- ‘Building Construction Handbook’ (6th ed.), CHUDLEY, R., GREENO, R., Butterworth-Heinemann (2007)
Featured articles and news
Have the pressures of the market shredded the core values of professionalism?
Lead times are a measure of the amount of time that elapses between initiating and completing a construction process.
Government releases first tranche of funding for removal of unsafe high-rise cladding.
How to ensure UK transport infrastructure copes with severe winter weather.
Location shortlist for controversial new footbridge revealed.
Under the Party Wall Act a property owner has the legal right to do works that might otherwise constitute trespass or nuisance.
BSRIA examine the 'unpredictable' 2018 global air conditioning market.
ICE publish new report calling for new sector-wide body to help avert structural failures.
The rainbow JCB will be making a welcome return to the London Build Expo on 23 and 24 October at Olympia.
An introductory article to external works - all activities carried out to the external environment of a building project.