Flooding in Colombo aggravated by human activity

With entire neighbourhoods flooded, traffic has been halted for at least three hours. The drainage system is the main factor, as clogging in smaller channels impacts the entire system. Loss of natural habitat, illegal settlements, and poor maintenance are the main culprits.

Colombo (AsiaNews) – Heavy rains have caused widespread flooding in many parts of Asia over the past week. Hong Kong recorded the heaviest rains since 1884. In Sri Lanka, entire sections of the capital Colombo have experienced heavy flooding.

Sri Lanka’s Department of Meteorology reports that the city received about 95 mm of rain. In two hours, some streets in the Maradana area were flooded with the water level reaching 60 centimetres.

Thummulla, Armour Street, Colombo Fort and surroundings were completely flooded, halting traffic for over three hours.

In the past three decades, flooding has been a recurring problem in Colombo, compounded by human encroachment on wetlands, expanding informal settlements, and inefficient urban drainage, resulting in smaller drainage channels becoming clogged, causing overflows in the main canal system.

“Torrential rains and extreme weather require a strong flood mitigation system because floodwaters could cause waterborne diseases by attracting mosquitoes,” senior engineers in the capital warn.

In addition to flooding, several trees fell near the World Trade Centre and the Magistrate Courts in the Colombo Metropolitan area.

As road works have damaged tree roots, so they “tend to fall during strong winds,” said Kailayar Ramesh, director of the Environment and Lands Department of the Colombo Municipal Council (CMC).

“The opening of the locks of Lake Beira and the use of the two rainwater pumping stations of the Colombo metro urban development project are immediate measures to control flooding,” said engineers Samantha Kahawita and Senarath Amaratunga speaking to AsiaNews.

“The CMC is working with the Sri Lanka Land Development Corporation (SLLDC) to implement drainage and canal clearance. The main reason for floods in metro Colombo is the dumping of waste in canals, especially plastic”.

“Another major reason is rapid urbanisation and expansion of the city that led to the replacement of permeable surfaces, such as soil and vegetation, with impermeable ones such as concrete and asphalt. This reduces natural water absorption and increases runoff into the drainage system, causing urban flooding,” the experts noted.

To sum up, “Floods in Colombo are caused by heavy rainfall and a macro-drainage system with insufficient storage, conveyance, and outflow capacity.”

“Blockages in drains and canals can also hinder water flow, contributing to flooding. Construction and development in flood-prone areas, including wetlands and riverbanks, can disrupt natural water flow and exacerbate flooding,” they added.

“After the recent floods, the Ministry has allocated Rs. 595 million from the Treasury to immediately start cleaning Colombo’s 44-kilometre canal network through the SLLDC.”

However, unresolved problems remain, in particular "illegal structures that are pending court cases, narrow stormwater pipelines, including the continuous dumping of waste into drainage. Canals are the main obstacles to flood mitigation,” said CMC Commissioner Bhadrani Jayawardena.

“Approximately, Rs 1 billion would be necessary to lay new underground stormwater pipelines. Currently, the CMC is working with the port authority to check if the Port City construction had an impact,” she added. 

But the “CMC is not maintaining the city’s drainage system. During the past three years, this negligence and illegal constructions blocking drains and canals have led to this overflow condition,” lamented Patali Champika Ranawaka, a former minister in the Sirisena administration.

“Apart from the major canal system, there are 53 minor canals that need to be maintained to prevent wastewater, illegally discharged sewerage water, including dumped garbage. CMC needs to pay attention to cleaning roadside drains and getting illegal settlements removed,” Patali added.

• sri lanka
• heavy rains
• flooding
• colombo
• drainage
• climate change