Bangkok
examines flood prevention plansDec 2011
Shani Wallis, TunnelTalk
Devastating
floods across wide areas of the Bangkok metropolitan area have prompted
engineers and officials in Thailand to address urgently needed programmes and
projects that would mitigate the annual threat and ensure that the city is
prepared to prevent any repeat of this typhoon season's economically and
socially crippling disaster. TunnelTalk Editor, Shani Wallis,
attended a press conference last week in Bangkok at which the tunneling society
of Thailand presented its undergroud proposal for long term flood mitigation
and control.
Bangkok
inundated
Flood water metres deep in the streets
and homes of Bangkok during September, October and November took a heavy toll
on the citizens and the fabric of the city. Incredibly, more than two months
after the first inflows, flood water still lies across low-lying areas of the
city's suburbs with fears of waterborne diseases and families struggling to
salvage what they can of their possessions still the focus of local news
reports.
Struggling now with the aftermath of
the worst floods in the city's recent history, engineers in Thailand have
mobilised to present new infrastructure projects that will prepare the city for
predictable flood events in the future.
Like so many cities that have
implemented comprehensive flood control systems, one of the leading plans that
is gaining political support for Bangkok is based on extensive underground
excavation with multi-purpose functionality possibilities. A plan to excavate a double deck
cut-and-cover facility beneath the existing six to eight-lane Eastern Outer
Ring Road that stretches 100km from the northern suburbs and runs parallel with
the river would deliver floodwater to the Gulf of Thailand.
At times of heavy flooding the entire
24m wide x 10m high cut-and-cover facility would provide a channel for
floodwater. During normal times, the lower deck would remain reserved as a
drainage channel while the upper deck would accommodate another six lanes of
highway traffic to the already heavily congested highway above.
The waters that flooded into vast areas
of the northern suburbs of Bangkok were created by a perfect storm of
circumstances, according to members of TUTG, the Thailand Underground and Tunnelling
Group that will host the World Tunnel Congress (WTC) and 38th General
Assembly of the International Tunnelling and Underground Space Association
(ITA) in May next year (2012).
Underground option gaining traction
as the possible solution for Bangkok
"First,
the heavy rains of two typhoons at the start of the season in August hit the
upper reaches and catchment of the Chao Phraya River," explained Zaw Zaw
Aye, Tunnelling Director of the Thai construction company Seafco and Secretary
General of the WTC organising committee. "After months of no rain, these
were held in the reservoirs which filled very quickly. At that point, another
three typhoons hit the area in quick succession and vast amounts of water had
to be released from the dams. The water
had to come down the Chao Phraya River to the Gulf of Thailand. The problem in the city is that rapid
urbanisation during recent years has seen new housing estates developed on land
that once accommodated traditional rice paddy fields on which the annual flood
waters were welcomed. In addition, urban
flood defences have not kept pace with developments that have blocked many of
Bangkok's klongs, or canals, creating development barriers to Chao Phraya River
flood waters."
When
water released from the dams came down the river it was evident that parts of
the city would flood. As well as the
klongs, Bangkok has flood control defences, including a set of new drainage
tunnels. The first, in the city centre
(5km long x 5m diameter and with a 60m3/sec capacity) is complete; another
is under construction (6km x 5m diameter); and two more are in the planning
stages (the 13.5km x 5m diameter Don Muang tunnel and the 9.5km x 5m diameter
Suan Luang Ro 9 tunnel which will drain an area of 85km2). But these were not able to help Bangkok to
full measure on this occasion.
Extent of the floods around
Bangkok's protected city centre
"The current systems can manage
between 6-10 million m3/day," explained Zaw, "but more
than 11 billion m3/day of water was coming down the river. The city
could only drain a third of it."
City authorities used all existing
systems, including floodgates and the diversion weirs on the klongs, to protect
the city centre, with the surge spreading out in three directions to inundate
the northern, eastern, and western areas. Even Bangkok's new international airport,
opened two years ago on the east side of the city, was not spared. Many had
warned against building the airport on the eastern flood plain.
Through all, Bangkok's metro system,
with some 21km of the 50-60km network underground and the rest elevated, never
shut down. "Some underground station entrances were closed,"
explained Zaw, who worked on the construction of underground sections of the
system, "but the network is designed for a 100-year flood and all, or
most, underground stations have elevated entrances as well as flood doors. I
personally went to see how the flood doors performed in the emergency as I was
involved in the design and installation of several."
As it happened, the metro was the only
reliable method of transport through the wider city, including into the flooded
areas on the elevated sections. "Buses could not operate and most private
cars were out of action or parked on the elevated highways out of harm’s way,
which completely chocked off the highways."
For other underground utility services,
the potable water system was affected initially but was returned quickly to
full service as much of the floodwater was not contaminated. The sewerage
systems backed up and overflowed, a situation that brought with it the threat
of waterborne disease and the liberal use of chlorine as a quick-fix response.
As well as damage to homes, shops and businesses, a visit to Bangkok last week
by TunnelTalk revealed
that even now there are stacks of sandbags on standby in the city centre. Small
walls with stiles over them have been built in front of some smaller shops as a
more permanent protection measure.
There is also still an acute shortage
of food, bottled water and drinks in the shops. There was no flood water to be
seen but reports were of many low-lying areas, some including luxury
residential estates, still remaining under water.
The aftermath of the disaster has
included heavy criticism of Thailand's new Government and its failure to
address the looming crisis, as well as inadequate management of the upstream
reservoirs where officials were caught out completely by the deluge.
The reaction by the Government and City
authorities has been to begin afresh the development of plans to prepare the
city for what engineers know will happen again. The rapid urbanisation of the city and
building on the natural floodways make a repeat of the disaster a certainty
without urgent action. The new network
of 5m diameter drainage tunnels is designed more for stormwater management, not
for a massive surge of water down the river from upstream. Something much more
substantial and of much greater capacity is needed, and tunnelling engineers in
Bangkok have illustrated how underground flood mitigation methods are the only
feasible option.
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Chicago TARP ·
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Tokyo G-CANS ·
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Hong Kong Drainage ·
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Kuala Lumpur SMART ·
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At a press conference last week TunnelTalk joined
the audience to hear of how systems such as Chicago's TARP, Tokyo's tremendous
G-CANS underground flood channels and retention caverns, Hong Kong's major new
flood control tunnelling networks and Kuala Lumpur's innovative dual purpose
Stormwater Management And Road Tunnel (SMART) project, have inspired Thai
engineers to develop their own Multi-Service Underground Tunnel System, or
MUSTS.
Proposed multi-purpose flood
relief project runs beneath the Outer Ring Road, first on the east side and
eventually also on the west side
"The underground addresses several
major issues," said Engineer Professor Dr Suchatchawi Vince Suwannasawat,
Dean of Civil Engineering at King Mongkut's Institute of Technology Ladkrabang
who is also President of Thailand's TUTG tunnelling society and Congress
Chairman of WTC 2012.
"First it avoids expensive
procurement of private property for new
surface
flood canal options; secondly it limits the impact of what will be a massive
construction operation to the corridor of an existing public highway."
The underground solution also better
allows for gravity-feed of the flood facility towards the sea, a major concern
for surface options that often require large pumping systems or deep cuts. In
operation, the lower deck of the underground facility would have a capacity of
130 million m3/day. This would increase to 260 million m3/day
with both decks of the facility turned to flood control mode.
In addition, the multi-service system
includes the possibility of generating power. Directing water down deep shafts
would create the necessary hydrostatic head needed to operate a turbine
installed in the bottom. Depending on the selected size of the project, between
200-600MW of electricity could be produced by extending the project's
multi-service system application.
At the press conference in Bangkok on
Wednesday last week, Dr Suwannasawat explained that Phase 1 of the project, for
the 100km facility under the East Ring Road, would demand a Government
investment of some 200 billion Thai Baht (US$6.3 billion). He went on to
explain that, set against the estimated 1.4 trillion Baht cost of the current
disaster, the project represents a proposal that should be advanced as soon as
possible. The multi-service functionality of the project also presents the
possibility of imposing tolls on the roadway to raise funding towards its
construction and maintenance. There is also potential for generating
electricity to support its own operating costs.
The project has won early political
backing with Deputy Governor Teerachon Manomaiphilbul of the Bangkok
Metropolitan Administration speaking in support of the proposal and urging the
central Government to implement the project stating: "It is a huge
investment and one that I agree with."
Global theme for international congress
In welcoming the 64-member
nations of the ITA to Bangkok in May next year and the anticipated 1,500-2,000
delegates, the TUTG Organising Committee has selected 'Tunnelling and
Underground Space for a Global Society' as its congress theme. The fact that
the host city has suffered the kind of natural disaster that looms large for
many of the world's other major mega-cities will certainly draw extra interest.
Delegates will be interested to hear
first hand reports of how the disaster happened, how the city coped and more
importantly how the Government, authorities and engineers plan to prepare the
Bangkok to avoid similar disasters in future.
MUSTS includes the potential for
generating electricity
The
experience will profile significantly also in the Congress Open Session,
organised by ITACUS, the ITA Committee on Underground Space that is examining
the development of resilient cities over the course of the next three years.
Launched
this year at the WTC2010 in Helsinki in May, the theme of Delivering Better and
Resilient Cities discussed in Finland, continues in Bangkok in May 2012 where
the forum will centre on Planning Better and Resilient Cities, before moving to
Geneva in 2013 where delegates will close the series with a discussion on
Deciding Better and Resilient Cities. A
special one-day registration is offered for delegates who would like to join
the Open Session as a stand alone event rather than the full tunnelling
congress programme. There is much to
consider and develop on this wide ranging and vital topic and Bangkok's recent
flood experience makes it a most appropriate venue for hosting the discussion
in May 2012. A welcome and invitation to
attend is extended to all from the TUTG Organising Committee.
References
Helsinki WTC2011 Congress video
report - TunnelCast, May
2011
Brisbane averts underground works
inundation - TunnelTalk, Jan
2011
Concerns and consequences of
seismic devastation - TunnelTalk, March
2011
Santiago Metro survives massive
earthquake - TunnelTalk, March
2010
