Bangkok - As flood season revisits Thailand, experts and policymakers look to 2011, which brought the worst floods in half a century, to glean lessons about how they might safely move floodwater through Bangkok, the Thai capital, should they need to.
“One thing we realized from last year’s flood is that our city’s drainage capacity is not enough,” said Chusit Apirumanekul, a climate information application specialist at the Bangkok-based Asian Disaster Preparedness Centre (ADPC) . “We need to do something from the lessons that we learned.”
Flooding is an annual occurrence in Thailand, most of which lies in the drainage basin of the Chao Phraya River flowing from the confluence of the Ping and Nan rivers in the north. In 2011 over 500 people died in the flooding that swept down to the centre of the Thai kingdom and the World Bank put the economic losses at US$45 billion.
In October the Department of Disaster Prevention and Mitigation (DPPM) reported that more than 2.4 million people in 28 of Thailand's 76 provinces were affected. But it was the duration of the floods that stands out in the memories of most residents. Much of flooding that struck the Southeast Asian nation started in late July 2011 and did not fully subside until January 2012.
High seasonal rainfall in the hilly north fed a gathering tide that slowly snaked down through the central provinces to the Gulf of Thailand. In Bangkok, a megacity of more than 10 million inhabitants and the nation’s industrial heartland, the water ran into a substantial bottleneck, stopping it from getting to the sea.
Since then the Thai government has spent millions of dollars on prevention measures to avert a similar disaster, mostly on dredging canals and building dykes and floodwalls around industrial estates.
IRIN asked experts in Thailand and abroad what the authorities could do to drain floodwater from the city more effectively if these measures failed.
“We have a big flood every five years in Jakarta [capital of Indonesia],” said Doddy Suparta, a water expert at Mercy Corps, a disaster relief NGO based in Indonesia’s “mega-delta” city, whose more than 10 million inhabitants are familiar with the risk of flooding.
In the rainy season water comes flowing into Jakarta from hilly regions that lie east and west of the city. “We had a major flood in 1997, then in 2002, and then again in 2007,” Suparta said.
To tackle this recurring problem, Jakarta’s authorities have undertaken the East Flood Canal Project, building a 23.5km canal to carry the overflow from seven major rivers - the Ciliwung, Cililitan, Cipinang, Sunter, Buaran, Jati Kramat and Cakung - to the sea.
In addition, the Jakarta Emergency Dredging Initiative to deepen and rehabilitate 11 major floodways and canals in the city will be completed by March 2017. The World Bank is providing $140 million for the project, with the Indonesian government supplying the remaining $50 million required.
In Bangkok the municipal authorities maintain more than 1,100 canals. “The drainage system was not created to deal with floods like this [in 2011]. The canals that we use to get floodwater out of the city were originally made for irrigation purposes almost 200 years ago,” the ADPC’s Apirumanekul told IRIN. “If you want to drain the water [from the city] fast, you need to increase the drainage capacity from the upstream part of the Chao Phraya River basin to the Gulf of Thailand.”
At Chulalongkorn University in Bangkok the Unit for Disaster and Land Information Studies, led by Thanawat Jarupongsakul, has proposed a 200km “super floodway” of widened canals to protect parts of the country from future flood disasters, and provide an emergency expressway for excess water, allowing it to pass through the city to the ocean.
The project, with an estimated cost of $1 billion, would link existing irrigation canals to help drain runoff, as well as raise roads leading to and from Bangkok six metres off the ground to act as dykes, preventing canal spillage. Jarupongsakul estimated that the proposed floodway could hold 1.6 billion cubic metres of water, and drain 500 million cubic meters of water daily.
This system would not only be cheaper than building a new waterway, but would also be energy-efficient by using the power of gravity to keep the water moving.
However, Lertchai Srianant, a water management officer in Thailand’s Royal Irrigation Department, noted that “The government has a plan to use a large retention area in the upper part of the Chao Phraya basin to store excess water, so the water level in the river will not be higher than the dykes at any point.”
Bangkok and Jakarta both use giant pumps to speed up the process of drainage. “North Jakarta is the lowest part of the city, so the water ends up going there. We have several big centrifugal pumps in that area. When the water reaches a certain height, the pumps turn on automatically and push the water out into the sea,” said Suparta from Mercy Corps.
A similar pump is located in central Bangkok, from where it diverts water that collects in a smaller basin that cannot drain naturally into the Gulf of Thailand, and pushes it into an underground tunnel so it can run into the ocean.
“When the water enters an area inside the dykes protecting inner Bangkok, the only way to remove it is by pumps. There’s quite some pump capacity, but by the time the water reaches the pumps there’s already been some significant damage,” said Adri Verwey, a veteran flood management consultant from the Netherlands who is assisting in projects for the Vietnamese and Brazilian governments.
At the height of the 2011 floods some residents on the outskirts of the Thai capital, where the water stayed high for months, called for the dykes protecting central Bangkok to be broken to allow floodwater to drain away through the city into the ocean.
“Bangkok is lower than mean sea level. This means that once water gets into the centre of the city it will not drain out easily,” Apirumanekul warned. “And since water in the city drains out through the Chao Phraya River, if the level of the river is high at that time, it could take a very long time and cause a lot of damage.”