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Water based transport, recreation from Bolgoda to Negombo:

Long-term flood mitigation in Colombo takes off



Nagalagama street pumping station

South Lock

Wellawatta outfall



Harshan de Silva

The ongoing monsoonal rains lashing Colombo and its suburbs remind us of the devastating floods last November even inundating Parliament building in the middle of Diyawanna lake. Many agencies in control of water bodies came up with a number of proposals to mitigate floods in the Colombo basin as frequent flooding affects the economy.

Canals which were filled with plants and mud due to non-dredging for years were dredged and cleaned. Obstacles that blocked the free flow of water were removed. Legal action was taken against people who dump garbage into the city canal network, in a bid to maintain them properly.

The drains connected to these canals were also cleaned and restored as immediate measures to avoid road and settlements getting inundated.

The Irrigation Department, Colombo Municipal Council, the Sri Lanka Land Reclamation and Development Corporation (SLLRDC) along with service personnel were engaged in this process on a day and night basis to achieve targets in flood mitigation.

Many phases

In the past five to six months the SLLRDC has completed many phases of its programme to control floods as stipulated in its immediate, short, medium and long-term plans to mitigate floods. Dredging of canals and cleaning of drains have been completed.

Chairman SLLRDC, Harshan de Silva who spoke to the Sunday Observer sometime back on the cleaning and dredging of canals initiated as a short term solution for flooding, is pleased with the progress of the short term program.

The creation of retention tanks to increase the retention capacity of rain water has seen a rapid progress with more than 80 percent work in the Rampalawatta, Thalawathugoda and Waters Edge retention tanks completed by the SLLRDC.

Beira Lake

"Eighty percent of the dredging on phase one of the Waters Edge retention tank is completed and now we are ready for the beautification part", said de Silva.

With the dredging of the Waters Edge retention tank the entire area has got a new look adding to the beauty of Parliament Drive. Restaurants and boat services for the use of the general public are to be initiated by the Urban Development Authority.

The second phase of the Waters Edge project will cover the interior parts of the area. De silva laments that the dredging of the Waters Edge retention tank got delayed due to the rainy weather.

"My target is to complete the first three lakes in the Colombo basin-Rampalawatta, Thalawathugoda and Waters Edge and the retention tank in Peliyagoda by the first week of August," he said.

Whilst working on Treasury funded short and medium term projects the SLLRDC is also now concentrating on the long term projects.

The Colombo basin canal network consists of the Dehiwala, Wellawatta, Kirulapone, Heen Ela, Torrington South, Torrington North, Torrington, Kotte South, Kotte North, Mahawatta Ela, Dematagoda, St. Sebastian South, St. Sebastian North Canals; main drains and the outfalls which connect these waterways to the sea.

"We are in discussion with the World Bank on a soft loan for long term projects, to improve the Wellawatta and Kirulapone canals, improvement of Maradana pumping station, improvement of Galle Face outfall, restoration of Mutwal tunnel, construction of a new tunnel in Mutwal, to repair the Nagalagama street pumping station and outfall, and to improve storm water retention areas," he said.

Beira Lake area

The SLLRDC, UDA and the CMC are working together to improve the East Beira Lake area with a linear park and nine model parks. The West Beira from the Defence Ministry, Army headquarters and Slave Island stretch has also to be improved by dredging and bank protection to make the entire Beira lake a clean water body. "To improve the water quality of the Beira Lake, we have to stop the polluted water from Norris and St Sebastian canals coming into it by diverting that water into a micro tunnel along D.R. Wijewardena Mawatha to the North outfall", he said.

Despite the diversion of water flowing on the St. Sebastian canal from the South Lock into a micro tunnel the existing pumping station at South Lock maintained by Sri Lanka Port Authority will also be improved enhancing the present water pumping capacity from 3.5 cubic metres to 5 cubic metres per second in case Beira lake is to be flushed or additional clear water is to be pumped into the lake," he said.

This will be done to preserve the historic value of these pumping stations which were constructed during the Dutch era.

The new Mutwal tunnel was also proposed to enhance the draining out capacity of the Greater Colombo basin by inlet channel branches from the existing Mutwal drain around 100 metres upstream of the crossing of the Port access road. A tunnel section with a 4 metre diameter and a length of 740 metres starting from Muthwella Mawatha is included in the project.

To minimise the flooding of Thunmulla-Colombo University area, a micro tunnel will be created to drain out the water directly to the sea. The project will be undertaken by the CMC.

Construction of a pumping station and widening of the existing gate at North Lock a main outfall draining out storm water collected in the Greater Colombo basin is also included in the project. The width of the opening is 5.4 metres whereas the width of the canal in the upper stream is 20 metres.

"Widening of the gate to a minimum width of 20 metres is of prime importance - with the construction of a pumping station with a capacity of 10 cubic metres per second in the event of higher water level in Kelani river than the water level in Colombo Basin", he said.

Construction of a pumping station with a capacity of 30 cubic metres is also identified as a vital solution to reduce the water level down stream of Parliament Lake. This will increase the flow rate at the outlet of Parliament Lake.

Emergency situations

"I think a pumping station at Gothatuwa will be helpful to face emergency flood situations although we have to maintain it throughout the year", de Silva said.

In addition to this the bridges across the Wellwatta and Kirulapone canals at High Level Road and Galle Road will also be done to improve the flow of water along these canals.

The improvement of the Madiwela East Diversion canal through bank protection from the stretch between Awerihena tank and Athurugiriya road and restoration and creation of two lakes at Kalalgoda and Madiwela are also included in the project.

"The lands needed for these retention tanks has to be acquired from private owners", he said. Another project is to link the Colombo network to Bolgoda basin through Weras Ganga basin covering the south western outskirts of Colombo.

"The natural water flow is from Highlevel road to Parliament. We are trying to divert a portion of water collected in the Parliament area to the Weras ganga basin after constructing a bund", he said.

"With the inclusion of the Madiwela South diversion to the Weras ganga project we are evaluating the designs which have been done earlier. We are working on a tight schedule. The survey is being done and land acquisition and research also," he said.

The Weras ganga project aims at developing Katu Ela, Depa Ela, Bolgoda Ela, Werahera Ela, Bokundara Ela to control frequent floods in Nugegoda, Rattanapitiya, Bolgoda, Boralesgamuwa North, Boralesgamuwa South, Maha Ela, Ratmalana, Moratuwa, Thumbowila and Weras ganga basin.

Floods in these areas are due to the structures constructed across these waterways to irrigate paddy lands. The situation has been aggravated due to the abandoning of these paddy lands and also due to construction of buildings in those paddy lands. Retention areas have been reduced. Although 1,276 hectares should be there it has been drastically reduced due to unauthorised structures.

The project will include dredging of 5.5 km of the Weras ganga, construction of 2.3 km long flood protection wall on the right bank, improvement of 65 hectares of Weras ganga swamp retention area, 132 hectares of Maha Ela marsh and low land retention area.

Channel improvement of the 1.58 Km of Nugegoda Ela and 1.76 Km of Delkanda Ela, 2.13 Km of Rattanapitiya Ela and the improvement of 36 hectares of retention area are also included in the project to control floods in Nugegoda and Rattanapitiya areas. Channel improvement of 2.4 Km of Bolgoda canal, 3.09 km of Depawa Ela, 980 metres of Werahera tributary, 2.7 Km of Maha Ela and the improvement of adjoining retention areas are components of the Weras ganga basin development project.

Under the same project improvement of 11,120 metres of urban drainage in Ratmalana and Moratuwa, creation of Kandawala and Telewatta retention pond and the channel improvement of the 1.25 Km of Katubedda tributary is included.

"We are redesigning plans to minimise the resettlement of people affected from these projects", he said.

The project area is situated in the Maharagama, Kesbewa, Boralesgamuwa, Jayawardenapura Kotte and Dehiwala-Mount Lavinia local government areas and the local authorities have been educated about the project .

"We are going to propose two new lakes-one between the Nugegoda Kohuwela marsh and one down stream of the Delkanda junction since there is no place to retain water", he said.

This project is scheduled to start by the end of this year with the approval of funds from the China Construction Bank for mitigation of floods. "At the end we want to see boats starting from Bolgoda travelling to Negombo. The network is there and there are huge obstacles. We are working on them. A lot of investors are keen to invest and the public also come up with various innovative ideas", he said.

"Double decker boats, floating restaurants, water sports, floating houses are some of the proposals submitted for consideration", he said. "In the next two three years we will be able to complete the project to minimise floods around Colombo city to a greater extent", he added. "Flooding is a phenomenon that cannot be avoided. Yet, I am confident that we can control floods to a great extent through the implementation of these projects", he said.

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