Socio-economic scene:

Flooding in Colombo

Sher Azad

The unseasonal rains this April may perhaps have reminded the denizens of Colombo of the ever-present threat of flooding. The unusual nature of these showers may perhaps also have put them in mind of the climatic changes that we appear to be experiencing, particularly since the abnormally cold spell in January.

The city of Colombo is particularly prone to flooding because it lies smack in the middle of the stretch of wetland which extends from the Muthurajawela marshes in the north to the Bentota river in the south.

Long years ago, when the Portuguese arrived, 'Colombo' referred to the area of the present Fort and Pettah. The area to the south and east were marshlands, except for a thin strip of land along the coast and another linking the Pettah to Hulftsdorp.

Low-lying areas of Colombo

The inhabitants of these areas generally kept to the high ground. Our ancestors were generally quite savvy about what should and should not be done.

The Dutch converted the marshes into the Beira Lake, but generally didn't fill any land. They built a generous system of waterways which helped keep the floods at bay. These waterways followed the natural flow of water as far as possible, and were part of a greater system which stretched from Chilaw to Beruwela.

It was the British who began aggressively to reclaim the wetlands, particularly around Slave Island: the land between Captain's Garden and the Pettah (where the railway yards are) and the area to the east of Kew Road and Vauxhall Street, for example.

Areas earlier considered unsuitable for long-term occupation became residential. To prevent the Kelani River from flooding the low-lying areas of Colombo, the British built a bund between Kolonnawa and Angoda.

Wetland areas

The rapid growth of Colombo following independence led to more and more reclamation of the wetland areas of the capital and the suburbs. This process was accelerated in the land boom of the 1980s, with uncontrolled filling up of the marshes taking place.

Entire hills in the Colombo suburbs were flattened to provide earth for landfill. Residual marshlands within the Municipality were gobbled up. Storm drains were paved over to make roads.

This process was repeated in the outlying towns, particularly in the new Capital, Kotte.

When Alagakkonara first built Kotte as a bulwark against the depredations of Aryachakravarthi seven centuries ago, he made use of the wetlands surrounding the peninsula to create a 'jala durga', a citadel surrounded on all sides except one by water.

The approach to Kotte was from the south, through Mirihana. The present approach from Colombo, the area between Welikada and Ethul Kotte, is largely land reclaimed from the Diyawannawa.

In the 1980s and '90s, the marshlands between Kotte and Colombo were filled extensively. Even lands designated as retention areas were reclaimed, both unofficially and with the government's blessing. Much of this reclamation took place using municipal waste, which polluted the water.

The storm water from Colombo 7, Colombo 5 and Colombo 8 tends to drain into the canal system between Kolonnawa and Nawala. It is this area which has been most affected by the filling of retention sinks.

Massive floods

The result was that, in the great flood of 1992, excess storm water which used to drain into these sinks had nowhere to go and, for the first time, the more luxurious parts of Colombo went under water.

This was a consequence of the haphazard, commerce-driven and often illegal reclamation of the wetlands of Colombo district.

Although the authorities had considerable modern measuring equipment at their disposal, this was not deployed, so flow rates in and out of the various marshes and other low-lying areas had not been researched sufficiently.

The upshot of all this was that unscientific landfill impeded the natural flow of water and the retention and speedy drainage of floodwater. No measures were taken in mitigation, apart from such bizarre 'solutions' as filling in the St Sebastian canal at Hulftsdorp. This again resulted in massive floods.

Recently, however the authorities finally started taking meaningful steps towards preventing flooding. Large retention reservoirs are being carved out of low-lying areas adjacent to Ethul Kotte, Pelawatte and Thalawathugoda, which should serve to take the edge off floods in the area around Parliament.

The Heen Ela/Goma Ela canal system in the area between Kolonnawa and Nawala has been widened and extended. Armed Forces personnel were deployed here and the work took place swiftly and efficiently.

Global warming

Several other measures are also being planned, mainly with a view to diverting floodwaters upstream of Colombo. Downstream, widening the Wellawatte Canal will serve to remove storm water from the Colombo South area much faster. Alternative solutions, such as pumps and tunnels, are also being considered.

However, it will not be sufficient to provide solutions to the problem of flooding as it exists at present.

The authorities need to start planning now to deal with conditions as they will be a decade or more in the future.

Under 'normal' circumstances, the system will be able to cope. However, greater and greater abnormalities may be expected in the weather patterns as a consequence of global warming. It appears to be that, in Sri Lanka's case, the climate is getting steadily wetter.

As the years go by, rainfall in the Colombo area can be expected to increase. Something needs to be done to deal with the resultant excessive storm water. Interim measures, such as the widening of canals and the creation of additional retention zones by excavating illegally filled lands, may not prove to be sufficient.