"Even at present, the area where the Galle bus stand is located is flooded with even a little rain. All the drains there get clogged, and even a minor rain would flood the area because there is no means for the water to drain away. Back when I was still schooling, I would take off my shoes and wade through the dirty water to get to town. So, throughout my life, I have been working on designing a drainage system for Galle."

Dr. Nadeesha Chandrasena, who designed an open drain system to handle solid waste in densely populated cities, explained the situation upon our inquiry about why Colombo and other highly populated cities like Galle are constantly flooded due to rains.

Despite how common it has become to see Colombo flooded even with the most minor rain, it creates severe difficulties for the daily lives of people, transportation, and business activities. In fact, it is a grave situation that needs a sustainable solution. According to a research paper on stormwater management in dense cities, the complex issues in stormwater management in densely populated cities like Colombo mainly arise due to uncontrolled urbanisation and rapid development. (Urbanisation, in this context, refers to new constructions, repurposing of existing structures, or subdividing plots.)

On one hand, solid waste scattered all over the city clogs the stormwater drainage systems, open drains, or canal networks. This causes the drains to overflow even during minor rain. A complete blockage of the drainage system across the city is akin to a sudden heart attack, leading to 'flash floods.' Urban solid waste that is not disposed of properly blocks the drains, causing flooding and, on the other hand, generates large amounts of solid waste debris as a consequence of the flood.

Why does Colombo city flood even with minor rain?

Densely populated cities in lower- and middle-income countries often experience the threat of frequent flooding. Cities like Colombo, Mumbai, Jakarta, and Dhaka are classic examples of cities with the said issue. When it comes to Colombo, its geographical location itself is a low-lying ground. The reason behind the naming of present-day ‘Kompanna Veediya’ as ‘Slave Island’ in the past is the fact that the area was surrounded by freshwater.

The country’s economic capital, Colombo, which is located in the Kelani River floodplain with a soil structure that does not support water drainage, is a region that receives a high rainfall and now due to its very high population density, unplanned development, and issues with waste management, is at the risk of being submerged in water even by a small rain.

"Economically and geographically, Colombo is a key strategic location in the region. However, topographically, Colombo is neither easy nor suitable for extensive development. Nevertheless, given that all the economic activities are concentrated in Colombo and we do not have more land or alternatives, this development in Colombo is inevitable," says Dr. Nadeesha Chandrasena. However, development and urbanisation must be sustainable.

Colombo suffers from severe housing poverty. 'Housing poverty' means the inability to acquire land suitable for housing regardless of the economic strength of the people. A significant portion of Colombo's population lives in low-lying areas prone to flooding, with inadequate facilities. The slum housing percentage in these areas is 47%. Additionally, areas that have been newly developed as middle-class residences often flood even with minor rain.

"Let's consider a bus for instance," Dr. Chandrasena begins to explain the situation with an example. "The maximum capacity of a bus is 40 passengers, and only that number of passengers can travel comfortably in the bus. Regardless, 80 or even 120 people board the bus. Why is that? That is because there is no other bus. The issue with Colombo is very similar."

However, due to the numerous other pressing issues that low- and middle-income countries like ours must prioritise, providing sustainable infrastructure solutions for such urban problems often gets pushed back.

"The very fact that a solution not being sustainable creates issues and disasters. The time to restore such situations is long and the process is costly. What we could do is to try to reduce the magnitude of the disaster, and that is where the new technology is needed," says Dr. Chandrasena.

The Colombo problem

The older parts of Colombo city were planned and built during the colonial period. In 1921, a pioneering urban planner, Sir Patrick Geddes, designed the city plan within Colombo's boundaries. However, with the rapid urbanisation and expansion, in 1948, urban planner Sir Patrick Abercrombie and architect Oliver Weerasinghe proposed building three towns - Ratmalana, Homagama, and Ragama - to accommodate the growing population. These were planned for a population of 40,000 each.

Today, over 600,000 permanent residents live within the Colombo Municipal Council area. Additionally, about 500,000 people come to Colombo daily for work or various services.

By now, all large plots of land around Colombo that could be developed have been extensively developed.

"In countries with available land, it is possible to distribute the population to other areas and control the density, decongest dense areas, and create satellite townships. Nonetheless our country is small, and all economic activities are concentrated in Colombo. So, despite various plans to relocate, people tend to gather back in areas like Maligawatta that could still accommodate the population. This is a challenge in distributing the population within Colombo's tolerable residential areas.

"This is not an issue in the administrative boundaries of Colombo. The entire country's economic activities are concentrated in Colombo, creating a societal environment. This makes it difficult to redistribute the population," says Dr. Chandrasena.

"When there is no space to create new residential areas within the Colombo city limits, areas like Malabe quickly developed to become residential. Malambe is one key reason for Kaduwela to become a Municipal Council. When you study the natural drainage map of the Colombo district, it is clear that the natural drainage network is directed towards the Kelani River through the areas of Malabe and Kaduwela. That means these areas are low-lying grounds. Due to new development works took place between 2000 and 2015, low-lying lands were reclaimed, plots were subdivided, and large-scale housings were built. However, in 2016, there was a major flood along with heavy rain," she says.

"'Housing poverty' can be explained through this example," she further elaborates. "There are large houses built at high costs in Malabe. However, as a geographical location, there are many problems there. In 2016, the entire area was flooded. So, despite the buildings being economically luxurious, the location suffers from housing poverty."

Over the past few decades, while Colombo city has rapidly developed with new buildings and urban beautification projects, the drainage systems have not been updated to match the changing urban landscape. Additionally, some construction projects have encroached on environmentally sensitive areas and low-lying lands. Moreover, the high population density has also led to problems with waste management.

One identified reason for flooding in Colombo is the addition of solid waste to the drainage system.

Research has shown that well-planned drainage infrastructure can successfully minimize the risk of flooding in densely populated cities in lower- and middle-income countries.

Therefore, establishing an efficient urban drainage system is crucial to minimize the risk of flooding.

Is there a solution?

We approached Dr. Nadeesha Chandrasena for this article because she and her team designed a 'smart' drainage system preventing blockages in stormwater drainage systems due to solid waste in 2014 and received a patent as well.

Designed to be built in two layers, this system traps solid waste on the upper layer with nets and releases only rainwater into the drain.

To explain how this system works, Dr. Chandrasena said, "Even if there is waste, water can still flow through this system. It traps the waste on the upper layer while sending rainwater down. When the waste fills up the upper layer, a message can be sent to the municipal workers. It is a bot-drain which can even automatically post on a community social media page about the waste blockage if the situation doesn't improve within an hour."

Thanks to the creation of this system, she received a scholarship to participate in a practical studies course at Singularity University at NASA Research Park. In 2016, she made it to the final round of the competition that selects the top 35 innovators under 35 worldwide by MIT Technology Review.

"Trash is scattered around the drains in town, including polythene and plastic. No matter how quickly they are removed, there will still be debris like dried banana leaves or plastic that get washed into the drains. This clogs the stormwater drains during rains, eventually causing the drains to overflow and even lead to serious situations like flash floods. In 2005, the Mumbai flash flood killed more than one thousand people," she says, explaining the reason for designing her drainage system.

Is the 'smart drain' a solution for Colombo?

When we posed this question to Dr. Chandrasena, she said the system needs to be studied further and researched before presenting it as a solution.

"The drain I designed was for my Ph.D. It is still at the initial stage. It would need to go through at least five more stages to be applicable to a city. It cannot be implemented in Colombo as it is.

"To utilise in a city in a country like ours, this drain needs to be cost-effective. If a regular drain can be built for 1000 rupees, spending 5000 rupees on this drain won't be practical. So, above everything, the solution needs to be cost-effective. There needs to be further research conducted to build this system with cost-effective material.”

"Secondly, it is not necessary for every place. It can be applied only to areas with high population density, areas more prone to flooding, and areas with more human activity - let's consider the Fort in Colombo, for instance - and such, only in places where the solution is needed.

"The other thing is, if we are to apply this practically, in my personal opinion, instead of installing new double-layered pipes, we should retrofit the existing ones with an upper layer. Next, we should implement this as a case study in certain areas and study it for at least a year. After that, we need to review if the process works well, what the shortcomings are, and where the blockages occur," she explained.

"Whatever the new invention may be, it should always be applied practically in a sustainable way," stated Dr. Nadeesha Chandrasena.
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Nadeesha has won double accolades at the Australian Good Design Awards 2024: Best in Class in Engineering Design and a Gold Accolade in Engineering. More information is available here.

In 2022, Nadeesha Chandrasena was honored with the Glorious Sirimavian Lifetime Achievement Award at the fiftieth anniversary Gala Night of Sirimavo Bandaranaike Vidyalaya in Colombo, Sri Lanka. This award marks a significant milestone in her life, as it recognizes her commitment and service to the world, bestowed upon her by her alma mater.

Nadeesha Chandrasena received the Ten Outstanding Young Persons of Sri Lanka (TOYP) Award for Environmental Leadership in 2017, presented by Junior Chamber International (JCI) Sri Lanka. This recognition highlights the leadership she demonstrated in enhancing the environmental sustainability of Sri Lanka. The JCI TOYP program formally acknowledges young individuals who excel in their chosen fields and exemplify the best attributes of the nation's youth.

Nadeesha Chandrasena was recognized as a finalist for the MIT Technology Review 35 Innovators Under 35 list in 2016. This honor was awarded by MIT Technology Review in acknowledgment of her invention of the Solid Waste Clog Resistant Open Drain concept.

Nadeesha Chandrasena was selected to participate in the Global Solutions Program (GSP) 2015 at Singularity University, USA. This intensive program brought together innovators, entrepreneurs, and futurists from around the globe to collaboratively tackle some of humanity's most pressing challenges using cutting-edge technologies. During this transformative experience, she engaged in diverse workshops, lectures, and collaborative projects, all aimed at fostering innovative solutions with a global impact. This opportunity broadened her perspective on global issues and significantly enhanced her skills in leveraging technology for societal good.
Oliver
Singularity University