2. HIGHWAY DRAINAGE
During rains, part of the rain water flows on surface and
part of it percolates through the soil mass as gravitational
water until it reaches the ground water below the water
Removal or diversion of surface water from the roadway
and adjoining land is termed as surface drainage.
3. REQUIREMENTS OF DRAINAGE
Adjoining land : The surface water from the adjoining
land should be prevented from entering the roadway.
Camber : The road surface should be provided with
sufficient camber to drain off the rain water quickly.
Gradient : In the areas of heavy rainfall minimum
gradient should be provided.
Cross drainage works : Cross drainage works should be
designed in such a way that the road surface is not
overtopped even at the time of highest flood.
Highest Flood Level (HFL) : The level of carriage way
should be kept at least 60 cm above the H.F.L.
4. REQUIREMENTS OF DRAINAGE
Side drains : The side drain should have sufficient
capacity and longitudinal slope to carry away all the surface
Intercepting drains : In hilly areas, intercepting drains
should be provided parallel to the road.
Water table : Highest level of ground water table should
be kept well below the level of subgrade, preferably by at
least 1.2 m.
5. SURFACE DRAINAGE SYSTEM
Side drains for road in embankment :
When road is constructed in embankment, it is necessary to
provide side drain on one side or both sides, Such side
drains should be constructed at least 2.0 m away from the
bottom edge of an embankment.
The depth of side drain is kept 1.0 to 1.5 m to prevent the
entry of drain water into the embankment.
6. SURFACE DRAINAGE SYSTEM
Side drains for road in cutting :
When road is constructed in cutting side drains are
provided on either side of road.
The drain should not overflow in any circumstances.
7. SURFACE DRAINAGE SYSTEM
Covered drainage trenches:
Closed side drains are preferred as open and deep side
drains are dangerous where space is limited. In such cases
covered drains of drainage trenches properly filled with
layers of coarse sand and gravel may be used. Coarser
gravel layers are provided at the bottom of the drain.
8. SURFACE DRAINAGE SYSTEM
Catch basin is a structure like chamber constructed on a
sewer line. Water from pavement surface is collected in
catch basin and discharged to the sewer line.
9. SURFACE DRAINAGE SYSTEM
Inlets is a structure constructed along the edge of the urban
road to discharge rain water into the storm water sewer.
Inlets is a concrete box with grating either at the top or on
the side. If grating is horizontal, it is called horizontal inlet.
If grading is vertical, it is called vertical inlet or curb inlet.
10. SUB-SURFACE DRAINAGE
Removal or diversion of excess soil-water from the
subgrade is termed as sub-surface drainage.
Sub-surface drainage is necessary in the following
When road is in cutting and water seeping from sides.
When road is near the foot of hill and is likely to be
damaged by water flowing down the hill.
When road is passing through plain area and water is likely
to be accumulated on sides.
Where water rises up to subgrade by capillary action.
11. SUB-SURFACE DRAINAGE
Lowering of water table :
The highest level of water table should be fairly below the
level of subgrade, in order that the subgrade and pavement
layers are not subjected to excessive moisture.
The water table should be kept at least 1.0 to 1.2 m below
the subgrade. In places where water table is high best
remedy is to take the road formulation on embankment of
height not less than 1.0 to 1.2 m.
12. SUB-SURFACE DRAINAGE
Controlling seepage flow :
when the general ground as well as the impervious strata
below are sloping, seepage flow is likely to exist. the
seepage zone is at depth less than 0.6 to 0.9 m from the
subgrade level, longitudinal pipe drain in trenched filled
with filter material and clay seal may be constructed to
intercept the seepage flow.
13. SUB-SURFACE DRAINAGE
Controlling capillary water :
A layer of granular material of suitable thickness is
provided during the construction of embankment, between
the subgrade and the highest level of subsurface water
table. The thickness of the granular capillary cut off layer
should be sufficiently higher than the anticipated capillary
rise within the granular layer so that the capillary water can
not rise above the cut off layer.
14. ROAD ARBORICULTURE
A The word 'arbori' is originated from the Latin world
'arbor' meaning a tree.
Thus, arboriculture means the tree culture or care and
planting of trees.
It is the usual practice to grow trees on both the sides of a
road especially in case of roads passing through country or
non-built up area.
15. ROAD ARBORICULTURE
To provide attractive landscape of road sides.
To provide shade to the road users.
To provide fruit bearing trees and timber.
To protect against moving sand in desert areas.
To intercept the annoying sound waves and fumes from
To help in the stabilization of the formation.
To prevent the bituminous road. surface from becoming too