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02 December 2011

THAILAND: Two days in the life of an urban flood expert


Image: A Bangkok resident watches as flood waters rise around him. 13 October 2011

BANGKOK, 2 December 2011 (IRIN) - As 16 billion cubic metres of flood water bore down on Bangkok in early October, international experts flew in to help the government deal with an unprecedented potential calamity.

One was Adri Verwey, an urban flood specialist from the Netherlands, another low-lying "delta" country that has honed its international reputation for water management through investments that protect the country's highest-density areas from even unlikely catastrophes that would only occur once in 10,000 years.

Verwey has worked for the past 40 years on flood forecasting systems, mostly in Asia, and is now the senior specialist on modelling systems at the Netherlands-based water resources management think tank, Deltares.

IRIN followed Verwey and his team in the Thai government's flood command centre from 10-11 November, when three out of Bangkok's 50 districts were ordered to evacuate while rising waters threatened to overwhelm the city's hastily constructed sandbag dykes and water pumping system.

"We do not have experience in dealing with such a serious flood; many local experts have never expected a flood would happen in Bangkok," said Barames Vardhanabhuti, a lecturer in the engineering department at Kasesart University.

One of the first steps was to gather data and satellite images from multiple government agencies, and then enter the information on topography, water levels and the city's drainage system (number of water pumps, canals, drainage capacity and speed) into a multi-dimensional modelling software, which generated worst-case flood scenarios.

The result was cartoon-like images of water spreading through the city, frame by frame.

Brainstorming

With northern Bangkok already under 1.6m of water and the capacity of existing dykes far too low to handle such a massive flood, Verwey proposed using soldiers to speed up sandbagging.

The city's main 170km King's Dyke needed to be sandbagged up to 1-2m higher to save the city's business and tourist hub from flooding, said Verwey.

According to the Ministry of Interior's department of disaster prevention and mitigation, 350,000 sandbags had been produced as of 2 November. The department planned to distribute an additional 250,000 sandbags to save the country's administrative and economic heart from the deluge.

In case water pumps and sandbagging failed to hold back the deluge from inner Bangkok, Verwey and army officials brainstormed possible next steps: cargo containers placed in openings under the railway tracks to block water from flowing into central Bangkok? Blowing up the sea dykes near the Gulf of Thailand to quicken drainage if floodwater made it to the southern coast?

But the focus was still on gathering data and working with the army on sandbagging plans.

Verwey met the army's chief of staff and presented the plan to the prime minister, who agreed to mobilize about 1,000 soldiers to inspect 80km of The King's Dyke twice a day and to help local residents place additional sandbags.

If the dykes were not reinforced by sandbags in time, said Verwey, water sneaking under the dykes could lead to a breach up to 100m wide - causing widespread flooding across almost all areas in Bangkok; at the time only 30 percent of the city was flooded.

Water pump inspection

Besides sandbagging to hold back floodwaters, the excessive amount of water that had already inundated the northern and eastern parts of the city needed to be drained.

Verwey's team inspected three of the city's 14 water pumping stations and declared two sites functional. At the third station, the team found eight out of 45 pumps non-functioning and the remaining ones working at less than capacity.

It was almost 9pm on 11 November when Verwey waded through floodwaters to inspect the Bang Sue canal, the last barrier between the water and Bangkok's inner city. He declared all of them functional.

"We are monitoring the pumps around the clock," said the water pump station master, who had used his own money to buy a fan to cool down overheated control units.

Nearby, residents filled the waterways with lotus-shaped boats made from curled banana leaves and marigold flowers as the country celebrated Loy Krathong - an annual full-moon festival to pay tribute to the water goddess.

Verwey left Bangkok on 20 November - one day after the prime minister declared central Bangkok safe, with floodwaters receding from most parts of the city, much in line with his simulations.

But for Verwey, the job is far from complete.

"We can expect the flood to continue to recede, but it will still take quite some time before outer Bangkok is completely dry," he said. "What is needed next is a thorough analysis of what has happened and how such a flood can be prevented in the future."

In December he and his colleagues will help the government draft a new plan for water resources management for the Chao Phraya Basin - which covers 30 percent of the country and houses 40 percent of the population.

- IRIN