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Managing water, preventing floods

May 29, 2010 4:35:08 PM- transcurrents.com

by Rajan Philips

Pre-monsoon rains in May wreaked havoc in as many as five Provinces. The Western Province was the worst, with all three Districts, Colombo, Gampaha and Kalutara recording significantly high rainfall over long durations. Puttalam District in the Northwestern Province, Galle District in the Southern Province as well as parts of the Sabaragamuwa and Central Provinces also received heavy rainfalls.

The cumulative effects were severe and extensive. The rains added a few more hundred thousands Sri Lankans to the national category of "internally displaced people." Properties were damaged and roadways became inoperable. Many areas in Colombo were badly affected by the rain including: Jawatta Road, Thurstan Road, Torrington Avenue and Wijerama Mawatha areas, as well as Borella, Dematagoda, Grandpass, Kotahena, Maligawatta, Maradana, Narahenpita, Nugegoda, Pettah and Rajagiriya. Coastal areas were affected in Puttalam while the Munamalwatta River flooded many areas in Kalutara.

The national parliament, built on an island on a lake, had to be closed because of flooding fears. Government’s plans for the first anniversary showcasing of the war victory over the LTTE were literally rained out. Now the scramble is on to clean up the city in time for the 2010 International Indian Film Academy (IIFA) awards celebrations scheduled for June 3-5.

Many roads and roundabouts within Colombo went under water, and the Colombo-Kandy Road was impassable at several places. The airport operations at Katunayake were badly affected and flights had to be diverted to Chennai. Vehicular access to the airport was impossible at times and a helicopter service was provided for wealthier passengers to access the airport. The new airport road under construction for ten years was a major cause of floods in areas around the airport – Wattala, Mabole, Ja-Ela and Seeduwa areas. The half-built road was preventing the flow of water like a dam and had to be blasted by the Navy to create an outlet.

The intensity and the duration of the storm was unusual. The Colombo Observatory reportedly recorded 132 mms of rain between 8.30 a.m. and 2.30 pm in one day, while 24 hour monitoring outside Colombo ranged from 95 mm to 313 mm. According to Indian observations, Kerala and other parts in South India have been experiencing even more intense pre-monsoon rainfalls, but there have been no comparable reports of flooding and damages.

The major cause of the floods in Colombo has been identified as the inadequacy of the drainage system. Omar Kamil, Chief City Administrator of the Colombo Municipal Council, has drawn attention to the under-capacity of the City’s drainage system, built in 1938 when Colombo’s population was 80,000, to meet the current conditions when the resident population is ten times more and another half a million visitor population is also there to account for.

Put another way, the built-up areas in the City have increased considerably reducing the green space for infiltration and increasing the volume of water that has to be drained out after every rain. This phenomenon is not limited to the City and the flood experience of outer districts attests to that.

What is worse, even the existing drainage system has not been properly maintained. Apart from garbage and dumping, there has also been encroachment onto drainage facilities involving unauthorized construction. According to Mr. Kamil, longstanding drainage canals like the Torrington canal and St. Sebastian canal were not functioning to capacity, affecting the runoff to the sea and spilling over to roads adjacent properties.

Wetlands and swamps help in retaining rainwater and help avoid floods in addition to their numerous ecological benefits. Failure to protect and enhance these wetlands, and, worse, the blatant abuse of wetlands for official reclamation and unofficial dumping are also a major reason for the floods.

The Water Cycle

Even before the floodwaters could subside, political mud was found in enough quantities to throw around. There are also plenty of easy targets for casting blame. Shanty dwellers and local authorities have received the bulk of the blame, even though they are the least resourced and powerless in the pecking order. The Urban Development Authority has been singled out for special blame by Ministers and Secretaries, conveniently forgetting that the UDA has been under the charge of UPFA Ministers and officials for sixteen years.

The gravity of the situation forced the President to declare a moratorium on ministerial jaunts overseas, and give priority to disaster management and relief measures. As long term solutions, Ministers and municipal leaders are musing about uprooting shanty dwellers without compensation, revamping the drainage system according to a new Master Plan, and digging large ponds to retain rain water and prevent flooding. But these measures by themselves can be counterproductive.

Shanty dwelling is a social problem that needs to be addressed on its own and not as a flood preventing measure. In nature’s water-cycle involving evaporation, condensation, precipitation, and surface runoff/infiltration, social control is feasible and applied almost totally in regard to the end phases of runoff and infiltration. Even here, the extent of control is negligible to the natural water balance but is vital to the survival and prosperity of societies.

In the hoary tradition of Sri Lanka’s hydraulic civilization, the emphasis was on the control of surface runoff and retention of large bodies of water for cultivation and food production. In pre-modern times, vast open spaces also facilitated infiltration of rain water into ground water. Modernity and urbanization have shrunk the open spaces and replaced them with impermeable built environment, thereby reducing the scope and opportunities for infiltration, and increasing the amount of runoff.

Engineers found ways for conveying the runoff as quickly as possible as a fluid nuisance away from the built environment. But the conventional engineering approach to continuously create capacity for ever increasing runoff involving the building of large ponds and conveyance channels as well as widening rivers – has found to be counter productive in many instances.

The more sustainable approach is to promote development and building activities that have low impacts on the natural system, and to undertake measures that will enhance the natural system – particularly the wetlands and rivers and waterways. Central to this approach is also the realization that rainfalls should not be treated as inconvenient runoffs causing floods, but a valuable resource that can be used in many ways. The same realization underpinned the old hydraulic civilization.