4 Components of a Road Surface Drainage System

The road surface drainage system is built to control rainwater runoff on the road surface and surrounding areas so that it doesn’t damage the road construction. For example, damage due to flooding on road pavement and damage to the road body due to erosion.

The components of the road surface drainage system consist of the following:

1. Cross slope of pavement and road shoulder
2. Side ditch
3. Culverts
4. Catch ditch

Let’s discuss it in more detail.

1. Cross slope of pavement and road shoulder

The cross-slope of pavement and road shoulder must meet the requirements so that rainwater that falls on the road surface can immediately flow into the side channel.

On flat and straight areas:

• The slope starting from the middle of the pavement is made to decrease or slope towards the side ditch.
• The slope of the road shoulder is 2% greater than the slope of the road surface.
• Normal slope on asphalt/concrete road pavement: 2-3%; weather-resistant solid aggregate road surface: 4-6%; gravel road surface: 3-6%; and dirt road surface: 4-6%.

In a straight road on an incline/descent area:

• The slope of the vertical alignment of the road in the form of an incline/descent needs to be considered so that water can flow quickly into the side channels.
• The maximum value of the pavement slope can be taken from the normal slope above.
• On incline or descent areas where the road slope is steeper than the road slope, rainwater runoff will flow in the direction of gravity along the edge of the pavement. To speed up the flow and minimize damage to the road, small ditches must be made across the shoulder of the road at a certain distance.

In the bend area:

• Consider the need for the road stops according to the horizontal alignment requirements of the road following applicable regulations.
• Starting from the outside of the bend and decreasing or sloping towards the inside of the bend for the pavement slope.
• The amount of slope is determined by the maximum value of the horizontal alignment slope requirement or slope requirement according to drainage requirements.

Also Read:

• 5 Reasons Underlying The Need for A Drainage System
• 5 Common Mistakes to Avoid When Designing Drainage
• Understanding Linear Drainage Channels and Its Types

Side ditch

Road-side ditches are channels created on the right and left sides of the road which function to collect and channel rainwater from the surface of the road pavement as well as drainage areas around the road-side channels.

The form of the side channel chosen can be based on the basic soil condition, flow speed, and groundwater depth.

Culverts

Culverts are drainage structures that give way to water from natural channels (ditches, small rivers, etc.) that flow across the road. Apart from that, it is also used to channel water from side channels on one side of the road to the other to be discharged outside such as valleys or rivers around the road.

There are two types of materials for culverts, namely reinforced concrete and steel. Reinforced concrete can have a circular or square cross-section (box culvert) of various sizes.

Meanwhile, steel culverts are more practical and have larger dimensions than concrete culverts. Circles and ellipses are the shapes of the cross-section.

Catch ditch

A catch channel is a channel made at the top of a side channel to intercept or capture water flow and dispose of it elsewhere. Thus, not all water flow from the drainage area will go to the roadside channel. Apart from that, the catch channel also functions to secure the stability of the cliff slope so that it doesn’t erosion occur.

Sometimes the side channel has to accommodate water that comes from a catchment area outside the road-side channel which has a large discharge. This can happen on roads in mountainous areas or hilly areas. In this situation, a catch channel is needed so that the dimensions of the roadside channel are not too large.

That is a discussion of the components of the road surface drainage system, which consists of a cross slope of pavement and road shoulder, side ditch, culverts, and catch ditch.

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