Chapter 4: Highway Drainage (Universiti Tun Hussein Onn Malaysia)

Highway Drainage is a process which
• diverts and removes water from the pavement surface
• controls and directs sub-surface water into proper channels
in order to protect the road from damage.
A well maintained drainage system
• enhances safety to motorists by removing water away from the road and pavement
surface
• prevents highway surface water from flooding neighbouring properties
• reduces the risk of water damage to the highway
Poor drainage can cause water spraying on the windshield, thus reducing visibility, and
reduces the grip between the tyre and the road which can lead to skidding.

1. 1
1
Chapter 6
Highway Drainage
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
2
HIGHWAY DRAINAGE HIGHWAY DRAINAGE HIGHWAY DRAINAGE HIGHWAY DRAINAGE
Highway Drainage is a process which
• diverts and removes water from the pavement surface
• controls and directs sub-surface water into proper channel s
in order to protect the road from damage.
A well maintained drainage system
• enhances safety to motorists by removing water away from th e road and pavement
surface
• prevents highway surface water from flooding neighbouri ng properties
• reduces the risk of water damage to the highway
Poor drainage can cause water spraying on the windshield, thus reducing visibility, and
reduces the grip between the tyre and the road which can lead to skidding.
Sources of water on highways:
(1) Surface Run-off – eg. from rain, snow and sleet
(2) Subsurface Run-off – eg. from streams and ground water
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
3
HIGHWAY DRAINAGE HIGHWAY DRAINAGE HIGHWAY DRAINAGE HIGHWAY DRAINAGE
EFFECTS OF MOISTURE ON: HIGHWAY SURFACE Stagnant pools of water on the road can:
- slow down traffic
- cause accidents due to skidding and low visibility
HIGHWAY STRUCTURE Surface run-offs and subsoil moisture can reduce the stren gth of the construction
materials:
- High moisture content in the subgrade will reduce the stability of the soil, leading to
pavement failure.
- Prolonged contact with water can cause stripping of aggr egates from the bituminous
pavement, leading to the formation of potholes which sl ows down traffic and causea
damages to vehicles.
SOIL Excess moisture content in the underlying soil can increase the weight of the soil and
increase stress conditions. These are the two main reasons fo r failure of slopes and
embankment foundations.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
4
HIGHWAY DRAINAGE HIGHWAY DRAINAGE HIGHWAY DRAINAGE HIGHWAY DRAINAGE
Flexible Pavements are prone
to waves and corrugations due
to poor drainage:
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
Rigid Pavements are prone
to failures caused by mud-pumping:

2. 2
5
CATEGORIES OF HIGHWAY DRAINAGE CATEGORIES OF HIGHWAY DRAINAGE CATEGORIES OF HIGHWAY DRAINAGE CATEGORIES OF HIGHWAY DRAINAGE
Highway drainage can be categorized as
1) Surface Drainage– removes surface water
2) Subsurface Drainage– removes subsurface water
3) Cross Drainage– allows flow of water from a stream crossing the path of a road
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
Surface Drainage
Cross Drainage
Subsurface Drainage
6
SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM
Surface drainage for rural highways should include adequ ate transverseand
longitudinal slopeson both pavement and shoulder to ensure positive runoff .
Besides this, it should also include longitudinal channels(ditches), culvertsand
bridgesto provide for the discharge of surface water.
Storm drainsand inletsare also provided on the median.
For urban highways, adequate transverse and longitudinal slopes are needed.
Longitudinal drains are usually underground pipe drains.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
Curbs and
Gutters
Longitudinal
Channels
Longitudinal Slope
Transverse Slope Surface Drainage
7
SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM
TRANSVERSE SLOPE To facilitate the removal of surface water from the pave ment surface in the shortest
possible time.
Roads have a slightly convex profile – the middle is higher than the edges.
The slopes are known as the camber or cross-slope.
The inclination of the slope depends on the type of p avement and amount of rainfall.
The cross-slope for the pavement is typically 2.0 – 2.5%.
Shoulders should also be sloped, usually 4.0%.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
8
SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM
LONGITUDINAL SLOPES To prevent water from accumulating on the surface.
To facilitate the removal of water along the longitud inal channels that run along the
side of the road.
A minimum gradient in the longitudinal direction is p rovided at cut-sections.
Slopes not less than 0.2% are provided for highways in ve ry flat terrain and 0.3% on
suitably crowned pavement. A minimum of 0.5% is recommended for curbed
pavements.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel

3. 3
9
SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM
LONGITUDINAL CHANNELS Longitudinal channels or ditches are constructed along th e sides of highways to collect
and transport surface water to nearby drainage channels or natural waterways
(streams or rivers).
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
10
SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM
CURBS AND GUTTERS Curbs help to control drainage by restricting the flow o f surface water and transporting
the water into underground channels.
(Curbs are generally built to prevent encroachment of veh icles on adjacent areas and
to delineate pavement edge)
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
11
SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM SURFACE DRAINAGE SYSTEM
GULLY AND SCUPPER DRAIN
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
12
SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM
SUBSURFACE WATER SOURCES The sources of subsurface water are as follows:
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
(1) Seepage from higher grounds
(2) Seepage
from road
shoulders
(3) Surface water that permeates through
cracks and joints in the road pavement
(4) Groundwater that moves up as a result of capillary action
Subgrade

4. 4
13
SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM
Subsurface drainage plays an integral part in the overal l highway drainage system.
Subsurface drainage should operate together with surface drainage in order to provide
an efficient drainage system for highways.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
Well systems
Drainage blanket
Drainage layer
Transverse drains
Longitudinal drains
Subsurface
Drainage
14
SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM
LONGITUDINAL DRAINS Consists of pipes laid in trenches within the pavement stru cture parallel to the
centreline of the highway.
The function of these pipes is to lower the water table below the pavement structure by
removing any water that is seeping through.
The water table should be 1.2 m below the subgrade.
If the soil is permeable, construction of longitudinal d rainage trenches with filter sand is
advisable.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
15
SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM
TRANVERSE DRAINS Transverse drains are placed transversely below the pavement, usually in a direction
perpendicular to the centreline of the highway.
The function is to remove the groundwater that has infi ltrated through the joints of the
pavements.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
16
SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM
DRAINAGE LAYERS Drainage layers consist of coarse material which allows wate r to flow from fine grain
material of subgrade soil to the coarse drainage layer, and finally to permeable pipes
laid within the layer.
The size and spacing of this subsurface drainage depends on the quantity of water
discharge, type of soil and type of drains used.
However, one disadvantage is that the fine soil may be tr ansmitted to the coarse soil
and eventually clogging the voids of the coarse soil.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel

5. 5
17
SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM SUBSURFACE DRAINAGE SYSTEM
DRAINAGE BLANKET
A drainage blanket is a layer of material that is highl y
permeable.
The blanket can be used to facilitate the flow of sub-
surface water away from the pavement.
It also facilitates the removal of water that has
permeated through cracks in the pavement, as well as
subsurface water originating from artesian sources.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
18
CROSS DRAINAGE SYSTEM CROSS DRAINAGE SYSTEM CROSS DRAINAGE SYSTEM CROSS DRAINAGE SYSTEM
CROSS DRAINAGE CULVERT Cross drainage culverts allow water from a stream to move from one side of the road
to the other without crossing the road surface.
These culverts should be placed at regular intervals along grades, below banked
seepages, and where water will run directly onto log la ndings or forest roads and trails.
The advantage of culvert installation is that it can move
water from one side of the road to the other without
eroding the surface.
Culverts are expensive to install and require frequent
maintenance.
Culverts need to be kept free of debris at all times. O therwise, they will clog up and
become innefective.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
19
CROSS DRAINAGE SYSTEM CROSS DRAINAGE SYSTEM CROSS DRAINAGE SYSTEM CROSS DRAINAGE SYSTEM
CROSS DRAINAGE CULVERT Types of culverts:
Pipe culvert Box culvert
Arched culvert Beam culvert
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
20
DRAINAGE DETERIORATION DRAINAGE DETERIORATION DRAINAGE DETERIORATION DRAINAGE DETERIORATION
There are no specific drainage deterioration types in hi ghways.
Damages to the drainage system is usually due to:
(1) Improper maintenance
(2) Low quality of material used
Damages can be triggered by heavy loads imposed, for example, heavy machinery
in construction works may impose load pressure to a subsurface drainage, causing the
drain pipes to be crushed or slightly damaged.
Common drainage maintenance problems include:
- Vegetative growth around pipe outlets
- Mowing clippings
- Rodents’ nests
- Sediment collecting on rodent screens
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
Crushed pipe
Gully blocked by
debris and vegetative
growth
Damaged gully

6. 6
21
DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE
One of the many tasks in Highway Maintenance is maintaining and repairing
drainage systems.
DRAINAGE INSPECTION The objectives of drainage inspection are:
a) To ensure that all drainage channels and structures are unobstructed.
b) To check culverts and drainage lines for structural damage.
c) To inspect check dams for debris and excessive erosion.
d) To investigate water ponding on or adjacent to surfaced areas.
e) To inspect the drainage system during or after every storm.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
22
DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE
DRAINAGE MAINTENANCE Defective or inadequate drainage causes most pavement failures and deterioration.
Pending or delayed runoff of surface water allows seepa ge into the pavement structure
unless the surface is tightly sealed.
Typical maintenance activities include:
a) Annual inspection (minimum maintenance)
b) Minor to major structural repairs
c) Replacement of materials or structures when needed
d) Erosion control
e) Logjam or obstruction removal
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
23
DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE
Surface Drainage Maintenance Surface drainage maintenance works include:
1) Mark and correct areas where pending (delayed runoff) occurs on surfaced
areas.
2) Correct water-logging problems by filling or raisin g depressions, and by
providing outlets for water blocked by high shoulders.
3) Control entry of storm water through pavement by sealing joints and cracks.
4) Keep unpaved roads crowned (provide camber/cross-slope) to prevent water
from remaining on the road.
5) Maintain crowns and superelevations with graders or drags.
6) Sweep and clean roads to prevent collection of debris in gutters and inlets,
which could cause delay in the removal of surface water
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
24
DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE
Shoulder Maintenance Shoulders should be smooth and graded to ensure the water drains from the surfaced
areas towards the ditch.
Eroded shoulder material should be replaced with new material.
It is important to keep shoulders bladed flush to the ed ge of the pavement (or slightly
below).
Slope away from the pavement to prevent water seepage into the
subgrade.
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel

7. 7
25
DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
Drainage Ditch Maintenance To maintain the drainage ditch, it is important to kee p it clear of weeds,
sediment, and other debris that obstruct water flow.
It is essential to maintain ditches as to line and grade, and also correct sags and minor
washout as they occur.
Side ditches can be usually maintained with graders.
26
DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE DRAINAGE MAINTENANCE
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
Culvert Maintenance Culverts should be clear from debris and sediment to preve nt water from undermining
the culverts.
Culvert inspection must be done frequently to determine whether they are functioning
properly.
Cleaning by hand is usually necessary after heavy rains.
27
HILL ROAD MAINTENANCE HILL ROAD MAINTENANCE HILL ROAD MAINTENANCE HILL ROAD MAINTENANCE
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
MAINTENANCE OF HILL ROADS Hills are subject to intermittent to continuous rains, som etimes
throughout the year, therefore the risk of slips and la ndslides
is high for hill roads.
Hill road pavements must be constructed of impervious material,
as moisture can undermine the structure and cause failure. Drainage is also an important
consideration for hill roads to safeguard the pavement.
To reduce risks associated with swelling soils under or nea r hill roads, several
maintenance works should be done as mentioned below:
(1) Slope Maintenance
BMaintain a positive slope in the backfill area next to t he road.
BThe recommended slope is 1 ft within the first 10 ft of the foundation.
BPlant trees on the slopes to prevent soil erosion cau sed by rains.
28
HILL ROAD MAINTENANCE HILL ROAD MAINTENANCE HILL ROAD MAINTENANCE HILL ROAD MAINTENANCE
BFC 3042 HIGHWAY ENGINEERING                                    Lecturer: Mr. Basil David Daniel
(2) Drainage Maintenance
BCatch-water drains, side-drains, catch-pits and culverts should be cleared of blockages
at regular intervals.
(3) Gutters and downspouts Maintenance
BGutters and downspouts should be inspected regularly.
BDebris should be removed and defects should be repaired.
BMaintain the slope of gutters to prevent debris collect ion and subsequent rusting of metal
materials.
BDownspouts should be clear of debris.
BDirect the water flowing through the downspouts away f rom the foundation.
(4) Splashblocks Maintenance
BSplashblocks should be long enough and sloped enough to carry all the water away from
the foundation.
(5) Subsurface Drainage Maintenance
BAvoid covering or obstructing the drain where it discha rges.
BNeed to be installed correctly in order to function pr operly and therefore require little
maintenance