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A boat transport system along canals:

Colombo will be floods-free soon

The 2010 November floods in Colombo and suburbs in which the Parliament, also went under four feet water compelling the MPs to reach the parliament in armoured vehicles became one of the decisive events in the recent past for the city planners to think twice about the future and ongoing city planning in face of alarming floods threatening the city.

Therefore, more than 400 millimetres rainfall experienced within 15 hours in Colombo, considered as the highest rainfall in recent history rang as an alarm bell to all the city planners to think more seriously about the flooding in the city.

This situation prompted the government to appoint a National Task Force on Flood Mitigation comprising representatives from all stakeholders in flood mitigation to decide on appropriate measures to manage such a flood situation to ensure smooth functioning of the Parliament and the day to day life of both commercial and administrative capital of the country.

According to Engineer Rohan Seneviratne, Additional Secretary to the Ministry of Defence and Urban Development and also the Project Director, Metro Colombo Urban development Project, after November 2010 floods immediate measures were taken to arrest the situation by creating lakes and improving the capacities of the lakes, improving the conveyance capacity of canals and stopping illegal land filling.

"That has given good results. But that is not the full solution. We have to give full solution for the flooding in the metro Colombo region. Under Metro Colombo Urban Development project we are trying to give total solution for the flooding in metro Colombo region", he said.

"There will be a lot of interventions under MCUDPs. More lakes will be created and the entire canal system will be rehabilitated and the Beira Lake will be restored to mitigate floods. Three pumping stations to pump flood water and two micro tunnels to channel water through underground to the sea will be constructed under this project", he said.

In addition, there will be micro area intervention and 15 critical places in the Colombo city which go under water will be improved under this project.

"Out of the 223 million US dollars funding by the World Bank for the entire project, about 150 million US dollars will be spent on flood mitigation purposes", he said.

The Sri Lanka Land Reclamation and Development Corporation (SLLRDC) as the main stakeholder in the flood control in Sri Lanka studied the main canal system in Colombo basin in preparation of total solution floods in the Colombo and suburbs.

The proposals prepared by the SLRDC along with other relevant agencies in the Task Force after conducting in-depth studies, are now ready to be implemented under the Metro Colombo Urban Development Project, the government's flagship urban regeneration program funded by the World Bank.

According to Engineer Thushari Andra Hennadige, Assistant General Manager (Special Projects) of the SLLRDC and also the Project Manager, Flood & Drainage Management Component of the MCUDP, the proposals to be implemented under this project aims at improving the drainage system in the Colombo basin to improve the flow of flood water to the

sea and Kelani river through the existing outfalls and through the introduction of new outfalls and micro tunnelling to the sea.

The Main canal system in Colombo basin is almost a natural drainage system. The outfalls of the system are connected to the sea at Dehiwala and Wellawatta and one small outfall at Mutwal and two outfalls to the Kelani river at Nagalagam Street and in Ambatale. In addition, storm water is also discharged through the Beira Lake into the sea through its outfall.

High intensity rainfall experienced within a short duration in the Colombo basin, the inadequacy of the outfall capacities of drainage network, conveyance capacity of the canals, reduction of retention areas, dumping of solid waste into canals resulting in reduction in capacity, unauthorised construction encroaching water bodies have to be addressed when preparing the total solution to the floods.

She said at the time of the last improvement of the canal system in Colombo in 1990s, they have assumed that there was 1,000 acres of the retention area in the Colombo basin. But "According to our studies the retention areas in the Colombo basin have been diminished by 40 percent and now we have only 500 to 600 acres of retention area because of the unplanned development and illegal constructions", she said.

"We studied the rainfall from 1869 to date in the Colombo basin and observed that there is an increasing trend in the rainfall during the past 30 years.

It is observed that we have experienced 450 mm daily rainfall events during that period. So we have to design the system to suit the climate change", she said.

These studies also have revealed that the conveyance capacities of the canals are not adequate enough to cater for the full outflow capacity of the existing outfalls.

That also becomes a hindrance for the maximum utilisation of these outfalls.

"To remedy this situation, we have to improve these canals. But it is very difficult to enhance the capacity of canals due to lack of space for widening", Engineer Thushari said.

The water level of the Kelani river becomes a vital factor in mitigating floods in Colombo as the Irrigation Department used to close the two outfalls to the Kelani river, at Nagalagam and at Ambatale when there is an increased water level in the Kelani river to protect the city from over flooding, confining the discharge of water only through the sea outfalls. When high water levels in Kelani and high rainfall to Colombo coincides it creates a huge flood risk in Colombo.

Under these circumstances when the Kelani water level is high, the only option available to reduce the water level, is to pump the water.

"Introducing pumping stations at the outfalls to Kelani we can get the maximum use of these outfalls. So we are going to introduce mainly two pumping stations and they will be located one at Nagalagam outfall and one at Ambatale", she said.

The improvement of the secondary drain network for prevention of local floods will be done with the involvement of the Colombo Municipal Council and other relevant agencies to prevent localised flooding.

Fifteen sub projects have been identified to be implemented to prevent localised flooding in the Colombo city.

"We realised that we cannot control floods effectively only through those improvements. We need some more outfalls to increase the outflow capacity. It is very difficult and we can hardly find a trace to construct a new open canal leading to new outfall.

The only way we could see this happen is by having an underground tunnelling system", she said. Since Colombo has developed so fast during the recent past it should avoid all the piling areas and the feasible option available is to construct them along the roads. But that will also be difficult due to increased number of utility lines.

"Under this project we have identified two traces for the micro tunnels. One in Colombo 14 area and the other in Torrington area.

"Lack of support from the general public, unauthorised construction with the encroachment of the canal banks, non availability of proper solid waste management systems, proper connection between the tertiary and secondary drainage systems, lack of awareness among the public, lack of coordination among relevant agencies are also contributing factors towards hampering proper flood mitigation measures," she said.

"Now the Ministry of Defence and Urban Development is going to put up condominiums for the low income people. Once these low income communities along the canal banks are resettled we get some space for the improvement of the canals system and the widening of the canals also", she said.

"After the full implementation of the project, we are going to look into the water quality improvement of these canals. As one measure to maintain a good water quality and also to assist the transport facilities in the Colombo city, a boat transportation system will be launched along canals. Some docking stations close to the bus stands will be set up to facilitate this boat service", she said.

Setting up of Real Time Control (RTC) system for prediction of floods and early warning for minimising of damages is one of the highlights of this project. With the completion of the entire project within the next two years the SLLRDC will have the facility to create the flood inundation maps and to do Flood Risk Assessment for future development activities.

Capacity enhancement for flood and drainage management would essentially require the formulation of an Integrated Flood Management System (IFMS) to ensure sustainability of project outcomes. The IFMS would need to essentially focus on Monitoring and management of the wetland areas, operation and maintenance systems for canals and wetlands, Monitoring and enforcement of land-use planning to safeguard the capacity of the system to cope with floods, Inter-agency co-ordination protocols and mechanisms.

This project from its outset has been under the guidance and close supervision of Secretary of Defence and Urban Development Gotabaya Rajapaksa. She said his pragmatic support is invaluable in the success of the project.

World Bank provides machinery and equipment worth Rs. 1,000 million for proper maintenance of the main drainage network of Colombo water basin which is essential for the sustainability of this project.

Two packages of the entire project is now at the implementation stage. According to Deputy Project Manager Indika Kahawita, the Main Drain and Dematagoda Canal development are the two ongoing projects and the construction work is due to be completed in May 2014. Main components of Main Drain Project are protection of canal banks with construction of crossing structures, improvements to the box drain and Mutwal Tunnel inlet and development of Mutwal sea outfall.

Under the project at Dehiwala, the canal banks are to be streamlined and protected and rock outcrops at the canal bed are to be removed. Therefore, the major components of the flood and drainage management in the Colombo city will soon be implemented to provide a total solution to the flood situation in Colombo not only making Colombo an attractive city, but a city resilient to floods under the Metro Colombo Urban Development Project.

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