Labahua: October 2020

Bangkok examines flood prevention plans Dec 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 38^th 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 develope 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.

Chicago TARP

Tokyo G-CANS

Hong Kong Drainage

Kuala Lumpur SMART

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