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Porous Asphalt: an initiative to save the sinking Dhaka City

  • Published at 04:33 pm May 3rd, 2019
Porous Asphalt
Photo: Mehedi Hasan

A smart solution to mitigate waterlogging in the capital

Waterlogging is a condition of land in which the soil profile is saturated with water either temporarily or permanently.

A recent report by Dhaka South City Corporation (DSCC) and Dhaka WASA identified about 48 waterlogging prone areas. According to them, the waterlogging prone areas are Mirpur, Shewrapara, Kazipara, Pirerbag, Mohammadpur, Uttara, Motijheel, some places of Puran Dhaka, Dhanmondi, Sobhanbag, Newmarket and many more.

Poor drainage pattern along with unplanned structure of Dhaka city and heavy monsoonal rainfall over a short period causes water logging problem. And soon the city is going to be hit by frequent waterlogging since monsoon is near at hand. Waterlogging poses unbearable traffic congestion which disrupts the natural traffic flow. Hence, it takes almost a double time to reach any destination. 

From my personal experience, it almost needs two hours or more to reach Dhaka University campus from Mirpur during rainfall, while typically it does not take more than an hour.

Possible Solution for the Waterlogging Problem

“Porous Asphalt” may be a possible solution to mitigate the waterlogging problem in Dhaka city. It is also known as Porous Pavement, Porous Concrete, Pervious asphalt, Open-graded asphalt, etc. It has been being used for than 50 years, but it was originally developed in 1970 at Franklin Institute in Philadelphia, Pennsylvania. Porous asphalt pavements are being used successfully throughout the United States.  

Porous Asphalt allows for percolation of water through hot-mixed with reduced sand or fines, which allows water to drain through it. Rain seeps into layers of rock and soil beneath the surface, where the water is then naturally filtered. Because this material comes in the form of concrete, asphalt, and pavers, it helps to increase or conserve the groundwater level.  

Figure: Cross section of Porous Asphalt

Porous asphalt surface mixes are also used instead of putting it over a stone recharge bed. It can be used as a thin surface layer on conventional highway pavements. Rainwater sinks directly into the surface and then hits the impermeable asphalt layer below forcing the water to drain off to the sides. This way is more suitable for us because it saves time and requires less capital.

Porous Asphalt vs. Drainage System

We know most of the water bodies in Dhaka city are full and it is both times consuming and costly to improve our drainage system. Furthermore, a huge amount of money is used for road maintenance every year. Adopting porous asphalt will reduce the maintenance cost as porous asphalt pavement surface cost approximately the same as conventional asphalt and mitigate water logging problem as well. As a result, the authority needs not to allocate budget for improving drainage system separately. 

Furthermore, Porous asphalt is fast and easy to construct. It is suitable for every climate and geography. This project is also environment-friendly. In comparison to the traditional dense-graded pavement, porous pavement is typically installed as an urban “best management practices” (BMPs).