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Last edited 07 Nov 2019
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 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.
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 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.
- 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)
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