ABSTRACT
One of the most important aspects of the design of a road is the provision made for protecting the road from surface water and groundwater. Water on the pavement slows traffic and contributes to accidents from hydroplaning and loss of visibility from splash and spray. If water is allowed to enter the structure of the road, the strength and deformation resistance of the pavement and subgrade wil l be weakened, and it wil l be much more susceptible to damage by the traffic. Water can enter the road as a result of rain penetrating the surface, or as a result of the infiltration of groundwater. When roads fail, it is often due to inadequate drainage. Water can also have a harmful effect on shoulders, slopes, ditches, and other features. Failures can arise spectacularly as, for example, when cuttings collapse or when embankments and bridges are carried away by flood-water. High water velocities can cause severe erosion, possibly leading to the road being cut. On the other hand, low velocities at drainage structures can lead to silt being deposited which, in turn, can lead to a blockage. Blockage often results in further erosion or overtopping and possibly wash-out.
