Necessity of good drainage:-

1) Road drainage is necessary to collect surface water in side drains and to keep road surface in dry condition.

2) It is also required to carry sub surface water away from sub layers in heavy rainfall regions

3) It helps to reduce occurrence of road defects due to rainwater and rise of groundwater

4) It is beneficial to minimize landslides and related undesirable effects.

5) It increases load carrying capacity due to dry condition and maintained density of sub layers

6) It also results a good durable road with lesser maintenance as well.