The road drainage system, as put on roads, covers removing water through the roadway, prevention of water from reaching the road and the controlled movement of water along and under the road.
The water involved may attain the roadway caused by:-
• Rain falling onto the roadway
• Surface run-off from adjacent catchment areas
• Underground water movement
• Moisture rising from your water table under the roadway.
The presence of water is undoubtedly the most common cause of road failures. Water saturating a sub grade or pavement may cause pavement failures; water running along the fringe of the pavement can cause scouring and water running down the batter of an embankment or cutting may cause serious erosion. Also the saturation of soil next to the batter is a type of cause of slips.
Consequently the soundness of a roadway depends largely upon an effective and adequate road drainage system . It is therefore necessary that a proper system be provided back then of construction and effective maintenance of the system be carried out during the life of the road. The significance of drainage cannot be over-emphasized.
The type of drains and drainage structures can be broadly listed under four classifications:-
(1) Culverts (pipes, box culverts, etc.)
(2) Surface drainage
(3) Flood ways
(4) Sub-surface drainage
The job plans, specifications and special provisions indicate the type and extent of road drainage system and stipulate the minimum standards of materials and construction.