The Sri Lanka Land Reclamation and Development Corporation (SLRDC), which maintains the major canals in the city has found that the main causes for floods are blocked drains and canals, unauthorised constructions and the century-old drainage system in the Colombo city, which fails to absorb the present high volume of water, or carry the water to the sea. These blocked drains and canals will be cleared soon under the first phase.
SLRDC General Manager Gamunu Allawattegama said that a coordinated effort, with the Colombo Municipal Council (CMC), Road Development Authority (RDA), Urban Development Authority, SLRDC and other state agencies, to have a sound flood retention system will be implemented soon.
According to Allawattegama, there was no major obstruction in the two major outfalls - Wellawatte and Dehiwala but the feeder canals that end up in major canals were blocked with garbage and the drainage system maintained by the CMC has not been rehabilitated for decades and could not absorb the high volume of flood water.
"The other main cause for this havoc is the filling up of flood retention areas, which were identified some years ago. Over 380 hectares of land in Heen Ela in the Kotte area, Kolonnawa and Nawala have been identified as flood retention areas but there are only 266 hectares of land remaining and the rest have been filled illegally", he said.
However, several measures have been taken to solve the problem. Instructions have been given to clear, de-silt and commence operations on the Mutwal Tunnel immediately.
"This has not been operational for years and once it is opened it can take five cubic metres of water per second and the floods in the northern region of the city can be solved", he said.
The second is the outfall to the Kelani Ganga, the North lock at Nagalagam Street which has the capacity of taking 10 cubic metres of flood water per second. A new pumping system will be introduced and the gates will be improved.
"The pump at St. Sebestian Place, which drains flood water to the Beira Lake will be re-activated and de-silted soon. The boulders lying underneath the Wellawatte canal when the bridge was built and the railway station are also blocking the smooth flow of flood water.
We will take steps to remove the boulders", Allawattegama added. According to the SLRDC General Manager, the 'mushrooming condominiums', which lack proper sewage and drainage systems, is another cause for frequent floods in the Colombo city.
"When the local authority and Condominium Authority approve building plans they pay scant attention to the drainage and sewage systems. The present drainage system in the city has not been rehabilitated in keeping with the rapid development in the city", he said.