Highway Drainage: Effects & types of highway drainage

Highway Drainage is the process of interception and removal of water from over, under and the vicinity of the road surface. After the precipitation, apart of water is lost by evaporation and transportation. A part is percolated and the remaining water is called surface water. The process of removal or diversion of this water is called surface drainage.

There is a water table below the subgrade of the road. The measures adopted to lower the water table is known as sub-surface drainage.

Types of Highway Drainage

1. Drainage in rural highway

The surface water is drained from the pavement surface through side drain which may be unlined and open. This side drain is trapezoidal in shape and provided at the suitable cross and longitudinal slope.

In the case of the embankment, the longitudinal drains are provided either on one side or both sides. In the case of cutting drainage is provided on both sides.

2. Drainage in urban streets

In urban areas, there is space restriction due to foot-path, dividing islands, etc. So, underground longitudinal drains are provided at the sides of the road.

Water drained from the pavement surface is carried forward in a longitudinal direction between the curve and the pavement for a short distance. This water is collected in catch pits at suitable intervals and led through an underground drainage pipe.

3. Drainage in hill road

Road drainage along with the water flowing down the hill should be efficiently disposal off down the hill constructing suitable cross drainage structures like drainage bridge, culvert, etc.

There should also be the provision of a catch drain at the upper hillside and side drains at the side of the road.

Effects and Importance of Highway Drainage system

1. It decreases the bearing capacity of the subgrade of the road.
2. Standing water on the highway reduces the coefficient of friction which is a danger for the high-speed traffic.
3. Formation of put holes, waves, and corrugation in the flexible pavement.
4. Water causes mud pumping in the rigid pavement.
5. It causes the erosion of the side slope.
6. It may cause the failure of a side formation slope.
7. Frost action at the cold region or during the winter season may cause the failure of the subgrade of the road.
8. We need huge amounts of money yearly in high maintenance.

Causes of moisture variation in sub-grade soil

The main causes of moisture variation can be grouped as:

A) By free water

• Seepage of water from higher ground level.
• Penetration of water through pavement.
• Transfer of moisture from shoulder and edge of the pavement.

B) By ground water

• Rise and fall of the water table.
• Capillary rise from lower soil level.
• Transfer of water vapor through the soil.

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