page_title: Bangkok
section_title: Topography
hierarchical_section_title: Bangkok / Geography / Topography
caption_attribution_description: English: Shortcut canals of lower Chao Phraya River
context_page_description: Bangkok is the capital and most populous city of Thailand. It is known in Thai as Krung Thep Maha Nakhon or simply Krung Thep. The city occupies 1,568.7 square kilometres in the Chao Phraya River delta in central Thailand and has a population of over eight million, 12.6 percent of the country's population. Over fourteen million people lived within the surrounding Bangkok Metropolitan Region at the 2010 census, making Bangkok the nation's primate city, dwarfing Thailand's other urban centres in both size and importance to the national economy.
  Bangkok traces its roots to a small trading post during the Ayutthaya Kingdom in the 15th century, which eventually grew and became the site of two capital cities: Thonburi in 1768 and Rattanakosin in 1782. Bangkok was at the heart of the modernization of Siam, later renamed Thailand, during the late-19th century, as the country faced pressures from the West. The city was at the centre of Thailand's political struggles throughout the 20th century, as the country abolished absolute monarchy, adopted constitutional rule, and underwent numerous coups and several uprisings.
context_section_description: Bangkok is in the Chao Phraya River delta in Thailand's central plain. The river meanders through the city in a southerly direction, emptying into the Gulf of Thailand approximately 25 kilometres (16 mi) south of city centre. The area is flat and low-lying, with an average elevation of 1.5 metres (4 ft 11 in) above sea level. Most of the area was originally swampland, which was gradually drained and irrigated for agriculture by the construction of canals (khlong) which took place from the 16th to 19th centuries. The course of the river as it flows through Bangkok has been modified by the construction of several shortcut canals.
  The city's waterway network served as the primary means of transport until the late 19th century, when modern roads began to be built. Up until then, most people lived near or on the water, leading the city to be known during the 19th century as the "Venice of the East". Many of these canals have since been filled in or paved over, but others still criss-cross the city, serving as major drainage channels and transport routes. Most canals are now badly polluted, although the BMA has committed to the treatment and cleaning up of several canals.
  The geology of the Bangkok area is characterized by a top layer of soft marine clay, known as "Bangkok clay", averaging 15 metres (49 ft) in thickness, which overlies an aquifer system consisting of eight known units. This feature has contributed to the effects of subsidence caused by extensive ground water pumping. First recognized in the 1970s, subsidence soon became a critical issue, reaching a rate of 120 millimetres (4.7 in) per year in 1981. Ground water management and mitigation measures have since lessened the severity of the situation, although subsidence is still occurring at a rate of 10 to 30 millimetres (0.39 to 1.18 in) per year, and parts of the city are now 1 metre (3 ft 3 in) below sea level. There are fears that the city may be submerged by 2030. A study published in October 2019 in Nature Communications corrected earlier models of coastal elevations and concluded that up to 12 million Thais—mostly in the greater Bangkok metropolitan area—face the prospect of annual flooding events.
  Subsidence has resulted in increased flood risk, as Bangkok is already prone to flooding due to its low elevation and an inadequate drainage infrastructure. The city now relies on flood barriers and augmenting drainage from canals by pumping and building drain tunnels, but parts of Bangkok and its suburbs are still regularly inundated. Heavy downpours resulting in urban runoff overwhelming drainage systems, and runoff discharge from upstream areas, are major triggering factors. Severe flooding affecting much of the city occurred in 1995 and 2011. In 2011, most of Bangkok's northern, eastern and western districts were flooded, in some places for over two months. Coastal erosion is also an issue in the gulf coastal area, a small length of which lies within Bangkok's Bang Khun Thian District. Global warming poses further serious risks, and a study by the OECD has estimated that 5.138 million people in Bangkok may be exposed to coastal flooding by 2070, the seventh highest figure among the world's port cities.
  There are no mountains in Bangkok. The closest mountain range is the Khao Khiao Massif, about 40 km (25 mi) southeast of the city. Phu Khao Thong, the only hill in the metropolitan area, originated with a very large chedi that King Rama III (1787–1851) built at Wat Saket. The chedi collapsed during construction because the soft soil could not support its weight. Over the next few decades, the abandoned mud-and-brick structure acquired the shape of a natural hill and became overgrown with weeds. The locals called it phu khao (ภูเขา), as if it were a natural feature. In the 1940s, enclosing concrete walls were added to stop the hill from eroding.
caption: Bangkok's major canals are shown in this map detailing the original course of the river and its shortcut canals.
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