City Hall refuses to be sunk by floods

City Hall refuses to be sunk by floods

Bangkok still lacks information about drainage problems

City Hall workers remove waste blocking Klong Lat Phrao in Huai Khwang district. Pornprom Satrabhaya
City Hall workers remove waste blocking Klong Lat Phrao in Huai Khwang district. Pornprom Satrabhaya

The Bangkok Metropolitan Administration (BMA) is preparing a major redevelopment of the capital's drainage system to increase its drainage capacity in a fresh drive to combat the city's flood problem.

Bangkok governor Chadchart Sittipunt chaired a remote meeting last month about water management with officials from the BMA's Department of Drainage and Sewerage, 50 district offices and state agencies to brainstorm ways to end the city's flood woes.

At the meeting, the department forecast rainfall across 60-80% of the capital this month, with accumulated amounts of 200-250 millimetres.

Mr Chadchart said the city has generally relied on two drainage systems -- canals and tunnels.

Up until now, the City Hall has carried out four tunnel projects -- the Prem Prachakon water diversion system, Makkasan swamp, Saen Saep and Lat Phrao canal tunnels, as well as the tunnel running under Bang Sue canal.

But these tunnels, stretching a combined 20 kilometres, can handle only 200 cubic metres (m³) per minute of water, far below the 2,000 m³/minute outflow required on the western and eastern sides.

Mr Chadchart said the city's core drainage system is the canal, which can help push water along routes to the Chao Phraya River. In this regard, the efficiency of the canal must be boosted rather than only focusing on tunnel projects.

"I believe the drainage system in the capital will get better," said Mr Chadchart.

To ensure the efficiency of the water pump, every spot across the capital must be checked including the electrical systems in 190 water stations.

Canal dredging is also necessary to drain water, in addition to a technique known as pipe jacking to increase the surface and ground water storage area. This will help with the drainage of excess water from community areas into the canal.

Overflowing canals can also be forked to drain into both tunnels and floodgates.

"Floodgates and canal dredging do not cost as much as tunnel projects. The most important thing is to develop canals and tunnels equally as both systems rely on each other," said Mr Chadchart.

However, the BMA's Flood Control Centre still lacks information about drainage problems in the heart of some communities, he said.

District offices must survey those areas and look for solutions while other agencies, such as the army, are also ready to provide help for people affected by inundation, he said.

Aside from the drainage systems, Mr Chadchart said rubbish is also a source of damage to the water pump. Mr Chadchart asked everyone to more litter-aware. BMA staff collect three tonnes of rubbish dumped in Bang Sue canal each day, while Rama IX's adjacent canal has even more debris, sometimes up to 5 tonnes, for officials to clear on a daily basis.

Mr Chadchart also sent his thanks to Prime Minister Prayut Chan-o-cha for allowing soldiers to help evacuate people affected by the floods.

The 1st Army Region had told the BMA of piles of rubbish stuck the Rama IX tunnel, connecting Saen Saep and Lat Phrao canals and Phra Khanong tunnel, causing a decline in its drainage capacity.

The army is also helping with dredging Lat Phrao canal in the north to make it deeper and increase its drainage capacity, while a similar operation in the south is being carried out by the BMA, Mr Chadchart said.

Apart from floods caused by rainfall, the issue seems to be aggravated by runoff and rising amounts of seawater.

The National Water Command Centre has followed up forecasts by the Thai Meteorological Department (TMD).

The TMD forecast heavy rainfall in some areas of the country during Aug 2-10 as a southwest monsoon blanketed the Andaman Sea and Gulf of Thailand while a monsoon trough prevails in Myanmar and the northern and upper northeastern regions of the country.

After assessing the water situation from the TMD and Hydro-Informatics Institute, the centre predicted that heavy downpours may lead to a build-up of water and flash floods and runoff in 38 provinces including Bangkok and its adjacent provinces.

Mr Chadchart said the Department of Drainage and Sewerage, with assistance from the army, the Royal Irrigation Department, TMD, National Water Command Centre and Electricity Generating Authority of Thailand stand ready to deal with problems as they arise.

Staff have also been stationed in certain spots to handle any inundation issues and provide prompt assistance.

The BMA also inspected the sturdiness of 79.63km of defensive lines set up in the capital with a capacity to handle 3,000 m³/minute of water flowing along the Chao Phraya River, Bangkok Noi, Mahasawat and Phra Khanong canals.

Bangkok also has flood walls stretching 88km, of which eight spots belong to the private sector.

The department has also been instructed to closely monitor 23 residential zones -- 14 spots in Phra Nakhon districts and nine in Thon Buri districts -- where the walls may have been damaged, he said.

Meanwhile, Sitang Pilailar, a lecturer at the Water Resources Engineering Department at Kasetsart University, recently said the city's sewers and drains are only able to run at 50% capacity.

According to the lecturer, with the aid of pumps, the city's canals and sewers should act as polders which drain excess water from the surface into larger bodies of water. As such, ideally, when rain falls, water on the streets will flow into sewers and canals before entering the Chao Phraya River.

The water level of the river is normally higher than the canals, so pumps play an important role in controlling the city's drainage system.

But everything now seems difficult to handle, with rubbish getting stuck in the sewers, Ms Sitang said.

At present, drainage pipelines zigzag underneath the city with little regularity, and sediments such as sand often flow into the sewers, adding to blockages that result in severe above-ground floods.

As waste water and rain water flow along the same pipes in the city, Ms Sitang suggested an increase in the capacity of the pipe should be made a high priority.

"As waste water and rain water are now going through the same system underneath the city, the BMA should increase the capacity of the pipes to ease the flood problems," Ms Sitang said.

She also suggested the BMA expand water-catchment areas to prevent floods, as well as invest in better weather forecasting and communication systems to ensure more precise forecasts and accurate feedback regarding the magnitude of flooding in each city area as they take place.

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