Bangkok plans at least 100bn baht in flood defences over 5–7 years

The Bangkok Metropolitan Administration (BMA) has drawn up a five-to-seven-year flood-management programme expected to require at least 100 billion baht, combining drainage maintenance with major canal, tunnel and water-retention projects to protect the capital’s role as Thailand’s economic centre.

The BMA’s programme follows flooding in Bangkok that has begun to ease but has caused widespread economic damage and disrupted daily life. Parts of eastern Bangkok remained inundated for at least a week as the drainage network struggled to move water arriving from multiple directions.

Bangkok accelerates drain clearing and canal upgrades

The BMA’s short-term measures call for accelerated clearing of more than 5,000 kilometres of drains, with work brought forward ahead of the rainy season.

BMA teams are also to monitor water flows, lower levels in smaller canals by draining them into main channels, and check that floodgates and pumps remain ready for use. Removing obstructions, particularly bulky rubbish, forms another part of the programme.

The BMA plans to work with residents to keep waterways outside their homes clear of rubbish and weeds that obstruct drainage.

Bangkok’s medium- and long-term programme focuses on improving canal capacity, particularly the north–south drainage network between Hok Wa Sai Lang Canal and Prawet Burirom Canal.

Bangkok has more than 2,000 canals, including over 30 major channels and 1,980 secondary canals. The proposed work involves deepening and widening channels and reducing bends to improve water flow.

Bangkok’s canal programme includes widening natural waterways and lining canal beds with concrete to speed drainage and limit soil erosion and bank collapse. The work faces both limited budgets and opposition from residents who want canals to retain their natural character.

The BMA also plans to address buildings encroaching on major canals to improve flows into seven large drainage tunnels, including the Rama IX and Bang Sue tunnels. Clearing these obstructions remains a lengthy task, alongside efforts to accelerate construction of six additional tunnels.

Bangkok targets 45 retention areas by 2027

Bangkok aims to expand its water-retention network to 45 sites with capacity exceeding 14 million cubic metres by 2027, building on the royally
initiated “monkey cheek” approach to holding floodwater temporarily.

The BMA currently has 38 retention areas with combined storage of 13,712,305 cubic metres. The city has expanded sites and improved their performance since 2022, with particular attention to eastern Bangkok, and is developing seven more areas adding approximately 290,000 cubic metres.

Four pond proposals rejected as two face cost questions

Four of six retention-pond schemes previously studied by the BMA’s Department of Drainage and Sewerage failed to secure local support during public hearings.

Two other previously proposed retention ponds, at Khu Bon Canal and Bang Chan Canal, cover approximately 130 rai and 39 rai respectively. The BMA has questioned whether land acquisition and construction would offer value for money compared with developing Nong Bon Lake, main canals and water-conveyance systems linked to the Nong Bon drainage tunnel extension.

The BMA’s City Planning and Urban Development Department disputed claims that the new city plan had dropped retention areas. The department said the six schemes had never been included in the current plan, attributing their exclusion to failure at the public-hearing stage.

Draft city plan would reduce floodway land to about a third

Asa Thongthammachart, director-general of the BMA’s City Planning and Urban Development Department, said the draft city plan would revise the broad floodway designation from about 100,000 rai to roughly one-third of that area, or more than 30,000 rai, to reflect existing urban development.

Asa said land still important for receiving and draining water would retain its green-hatched designation on the planning map. The BMA has continued to apply relatively strict controls on land use in these areas.

Asa said the draft plan would include a water plan setting out drainage routes and floodways systematically, bringing water management into land-use planning. Earlier arrangements had partly relied on green-hatched zoning, while the Town Planning Act 2019 provides for water plans as a component of comprehensive city plans.

Bangkok’s earlier floodway framework covered broad areas linked to Pathum Thani and Samut Prakan and had been subject to development controls for more than 40 years, Asa explained. Expanding communities, factories and housing projects, particularly in the two neighbouring provinces, meant the original floodway could no longer be preserved in full.

The eastern Bangkok drainage network connects north–south and east–west canals. Saen Saep Canal forms an important route from Min Buri towards Nong Chok, while Prawet Burirom Canal runs east–west and connects with north–south channels carrying water towards lower-lying areas and the sea in Samut Prakan.

Eastern districts including Min Buri, Nong Chok and Lat Krabang occupy low-lying land that receives runoff. Lat Krabang’s basin-like terrain makes drainage particularly difficult during heavy rain.

Public infrastructure serving eastern Bangkok, including Suvarnabhumi Airport, King Mongkut’s Institute of Technology Ladkrabang and urban rail systems, has encouraged urban expansion and greater demand for land, according to the BMA’s planning explanation.

The BMA said the draft plan would retain land still capable of storing and conveying water, particularly along canals and in eastern Bangkok, while reviewing other land uses according to each area’s potential and constraints. The stated aim is to balance flood management with urban development, social needs and residents’ quality of life.