Water based transport, recreation from Bolgoda to
Long-term flood mitigation in Colombo takes off
Nagalagama street pumping station
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.
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.
"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
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.
"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
"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
"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.