Better planning regulations needed to reduce flash flooding

Colombo (IRIN): Strict regulations preventing the building on, or blocking of, drainage channels need to be implemented if Sri Lanka is to have fewer urban flash floods, experts say.

The densely populated Western plains experienced the second flood in less than six months when over 315,000 people were marooned after exceptionally heavy rain on 10 November. Earlier, in the third week of May, flooding hit 672,000 people in southern and western Sri Lanka, killed 22 and damaged 900 homes.

“We have to seriously think about making sure that we do not block the drainage and [channel] systems,” said Ananda Mallawatantri, Assistant Resident Representative of the UN Development Programme (UNDP). “Otherwise the rainwater will have nowhere to flow.”

UNDP has funded a community drainage channel clean-up project carried out by the government’s Disaster Management Center in the capital Colombo and outlying areas. “The flood waters receded last week because some of the channels and drainage systems were clear,” Mallawatantri said.

UNDP spent US$ 100,000 in the first cleanup project in 2006 and another $50,000 on the second which began in May and ended recently.

Other bottlenecks which were hampering water flow had been cleared during cleanup operations carried out under a dengue prevention campaign this year, he added. “Luckily the water levels of the main river in Colombo were also very low, allowing water to flow out quickly.”

On 11 November the city canals were full, making most roads impassable. “However, by 12 November due to previous efforts… after previous floods to clear canals, drainage and waterways, water levels receded rapidly,” according to an assessment report by the UN Office for the Coordination of Humanitarian Affairs.

Experts at the Met Office told IRIN the western plains should be prepared for periodic heavy rain and flooding. “There is a pattern, and every year during April-May and towards November there is high rain,” said the Director, Gunavi Samarasinghe.

However, the 440mm of rainfall — the highest daily figure in 18 years — which fell on 10 November, was a very rare occurrence and unlikely to be repeated any time soon, he said, adding that the short duration of last week’s downpour may also have helped the water recede fast.

Urban flooding is becoming more common in Sri Lanka due to buildings blocking drainage systems, natural channels and low-lying areas.

The two floods in 2010 affected nearly a million people. The Government has allocated almost $1 million for relief work and compensation.