Function of Surface drainage:

The function of Surface drainage is to drain the water from the pavement surface and the shoulders during the rains and to divert it to the road-side drains such that the entry of water into the pavement layers and the subgrade soil is minimized.

Function of Sub-surface drainage:

The function of sub-surface drainage is to intercept the ‘seepage flow’ of water and divert the same away from the roadway to the nearest water course. The sub-surface drainage system also helps in lowering the ground water level well below the subgrade and in controlling the capillary rise of water.