Road drainage


The road drainage system is used to remove and dispose of surface and subsurface water. It maintains the road’s stability and durability by keeping it as dry as possible. Water becomes more prone to contamination the longer it remains on a surface. Highway design and construction are not complete without the installation of suitable surface and subsurface drainage systems.

Purpose of road drainage

  • Road drainage keeps the road surface and foundation as dry as possible. 
  • It maintains the road’s durability and stability. 
  • To maintain highway transportation at a low cost, a good drainage system is necessary.

Why is drainage needed for roads?

Road drainage systems are installed to collect surface water run-off and protect the road’s surface and subsurface from flooding. It is required for the following reasons:

  • Prevent seepage, ponding, and flooding.
  • Keep the carriageway, cycle way, and footpath free of water.
  • Maintain as much dryness as possible for the underlying road structure.
  • Prevent damage from hazardous surface water.
  • Preventing surface water from flooding adjacent properties

Road Drainage System Requirements

The following are the requirements for a successful roadway drainage system:

  • The carriageway’s and shoulder’s surface water should be adequately drained off.
  • Surface water from adjacent land should be kept out of the roadway.
  • To remove all of the surface water gathered from the road, the side drain must have enough capacity and a longitudinal slope.
  • The flow of surface water across the road, shoulders, and slopes should not cause erosion or cross ruts.
  • It is important to effectively intercept and drain off seepage and other underground water sources.
  • Special precautions should be taken in water-logged areas.
  • The road surface needs to have a good camber so that water can drain off quickly.

Types of Road Drainage System

There are numerous drainage systems with various design attributes and features that can be utilized to manage flows and treat water quality. Below, each of them is further explained:

1. Surface drainage system

Surface drainage is a system that collects and disposes of road surface water within the roadway.
This system prevents surface water from flowing from the pavement’s surface to the shoulders and into the road pavement’s sub-grade or any other layer.

Surface drainage’s functions:

  • To prevent water from draining from the road’s surface.
  • To keep the surface of the road dry with water.
  • The flow of gravity-collected water to a nearby natural stream or river
  • To improve the stability of all pavement types.

Types of surface drainage:

The side gutter

A side gutter is what the drain provides as a parallel to the road for the purpose of collecting and removing surface water.
By including a side gutter or side drain in the embankment and cuttings, surface drainage is effectively accomplished.

The side gutter’s portion is often carved in a triangular or trapezoidal shape.

Side drains are typically installed alongside roads with shallow design depths and moderate traffic.

Side gutter function:

  • The side gutters’ primary purpose is to collect surface water.
  • Eventually, these drains will connect with a river or other natural stream.
  • This side gutter is inexpensive, simple to build, and easy to maintain, but it has an unappealing appearance due to the deep ditch and is therefore undesirable when traffic is heavy.

Catch water drain

Water drains are additional gutters or road drainage systems that are installed parallel to the road at high elevations for the collection and discharge of surface water.

Since sloping land contains more water, it gains velocity as it approaches the gutter.

Since this can cause the ground to sink and the drain to be damaged, water drains are only provided on sloping terrain near the roadside.

Catch-water drains’ functions

  • The catchwater drain accepts a significant quantity of surface water flow while also breaking continuity.
  • The flow thus decreases the velocity of the water, preventing erosion and landslides and safeguarding the side gutter.
  • It also helps reduce size.
  • If the surface water flowing from high-level land to the roadway is large, it is preferable to collect it at regular intervals and then allow it to flow through the road embankment via a pipe drain.

2. Sub-surface Drainage System

Subsurface drainage is the process by which the pavement beneath which water is collected and removed is drained.

Sub-surface drainage is the most effective method of controlling moisture in all forms of road subgrades.

Controlling the moisture of the road subgrade is more important because if the moisture that builds up in the subsoil is too much, the road structure weakens.

Subsurface Drainage’s Functions 

  • To keep road subgrades dry.
  • Preventing water ingress into subgrade soil also maintains its carrying capacity. 
  • Water occasionally rises to a sub-grade from groundwater due to capillary action, reducing the growth of capillary. 
  • This can be managed by adding an impermeable bituminous layer or a cut-off layer of granular material.

Also Read:  Road Sign | Pavement Markings | Types of Pavement Markings| Roadway Marking | Parts of Road Way

Advantages of Road Drainage

  • Excess water that accumulates above ground can create an environment conducive to mosquito breeding.
  • Stationary water can contaminate the soil and lead to corrosion.
  • A drainage system might help solve this issue by removing toxins from your yard.

Disadvantages of Road Drainages

  • A higher upfront payment is required.
  • Repair projects are expensive and disruptive.

Road drainage issues that lead to defects

Improper highway drainage causes road deterioration in the form of the following defects:

  • Erosion formation results in disembarkment along the roadside.
  • Pavement edge dislocation caused by excess water
  • Bitumen stripping from aggregates, such as loosening or detachment of some bituminous pavement layers
  • Development of potholes
  • Failure of soil slopes due to an increase in weight caused by excess moisture
  • Wave and corrugation formation in flexible pavements
  • A reduction in the bearing capacity of subgrade soil
  • A decrease in soil mass
  • Shoulder distress at the pavement edge

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