|
A boat transport system along canals:
Colombo will be floods-free soon
By Ranil Wijayapala
 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. |
