Editing Bangkok (section)

===Topography===
Bangkok is situated in the Chao Phraya River delta in Thailand's [[Central Thailand|central plain]]. The river meanders through the city in a southerly direction, emptying into the [[Gulf of Thailand]] approximately {{cvt|25|km}} south of the city centre. The area is flat and low-lying, with an average elevation of {{cvt|1.5|m}} [[Above mean sea level|above sea level]].<ref name="Sinsakul">{{cite journal|last=Sinsakul|first=Sin|title=Late Quaternary geology of the Lower Central Plain, Thailand|journal=Journal of Asian Earth Sciences|date=August 2000|volume=18|issue=4|pages= 415–426|doi=10.1016/S1367-9120(99)00075-9 |bibcode= 2000JAESc..18..415S |issn=1367-9120}}</ref>{{efn|The BMA gives an elevation figure of {{cvt|2.31|m}}.<ref name="BMA geo"/>}} 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 [[Chao Phraya River#River engineering|several shortcut canals]].

[[File:Chaophrayashortcut.jpg|thumb|left|upright|Bangkok's major canals are shown in this map, detailing the original course of the river and its 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".<ref>{{cite book|first= H. Warrington |last=Smyth|title=Five years in Siam: from 1891 to 1896|year=1898|place=New York|publisher=Charles Scribner's Sons|volume=II|page=9}} Quoted in Baker & Phongpaichit 2005, p.&nbsp;90.</ref> Many of these canals have since been filled in or paved over, but others still crisscross 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.<ref>Thavisin et al. (eds) 2006, p.&nbsp;35.</ref>

The geology of the Bangkok area is characterised by a top layer of soft [[marine clay]], known as "Bangkok clay", averaging {{cvt|15|m}} in thickness, which overlies an [[aquifer]] system consisting of eight known units. This feature has contributed to the effects of [[subsidence]] caused by extensive groundwater pumping. First discovered in the 1970s, subsidence soon became a critical issue, reaching a rate of {{cvt|120|mm}} per year in 1981. Ground water management and mitigation measures have since lessened the severity of the situation, and the rate of subsidence decreased to {{cvt|10|to|30|mm}} per year in the early 2000s, though parts of the city are now {{cvt|1|m}} below sea level.<ref>{{cite journal |last1=Phien-wej |first1=N. |first2= P.H. |last2=Giao |first3=P |last3=Nutalaya |title=Land subsidence in Bangkok, Thailand|journal=Engineering Geology|date=2 February 2006 |volume=82|issue=4|pages= 187–201|doi=10.1016/j.enggeo.2005.10.004|bibcode=2006EngGe..82..187P }}</ref>

Subsidence has resulted in increased flood risk, as Bangkok is already prone to flooding due to its low elevation and an inadequate drainage infrastructure,<ref>{{cite news |last1=Deviller |first1=Sophie |title=With rising sea levels, Bangkok struggles to stay afloat |url=https://phys.org/news/2018-09-sea-bangkok-struggles-afloat.html |access-date=25 July 2019 |work= phys.org |date=2 September 2018}}</ref><ref>{{Cite web|last=Gluckman|first=Ron|title=Bangkok: The sinking city faces severe climate challenges|url=https://www.preventionweb.net/go/65887|access-date=2020-11-15|website= preventionweb.net|date=11 June 2019 |publisher=[[Urban Land Institute]]|language= en|archive-date=27 May 2021|archive-url=https://web.archive.org/web/20210527104222/https://www.preventionweb.net/news/view/65887}}</ref> often compounded by blockage from rubbish pollution (especially plastic waste).<ref>{{Cite web|last=hermesauto|date=2016-09-06|title=Plastic bags clogging Bangkok's sewers complicate efforts to fight floods|url=https://www.straitstimes.com/asia/se-asia/plastic-bags-clogging-bangkoks-sewers-complicate-efforts-to-fight-floods|access-date=2020-11-17|website=The Straits Times|language=en|archive-date=14 August 2020|archive-url=https://web.archive.org/web/20200814062209/https://www.straitstimes.com/asia/se-asia/plastic-bags-clogging-bangkoks-sewers-complicate-efforts-to-fight-floods|url-status=live}}</ref> 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.<ref>{{cite journal|first= Surapee|last=Engkagul|title=Flooding features in Bangkok and vicinity: Geographical approach|journal=GeoJournal|volume=31|issue=4|year=1993|pages=335–338|doi=10.1007/BF00812783|bibcode= 1993GeoJo..31..335E|s2cid=189881863|url=https://link.springer.com/article/10.1007/BF00812783|access-date=1 February 2020|archive-date=27 June 2021|archive-url= https://web.archive.org/web/20210627201335/https://link.springer.com/article/10.1007/BF00812783|url-status= live|url-access=subscription}}</ref> Severe flooding affecting much of the city occurred in 1995 and [[2011 Thailand floods|2011]]. In 2011, most of Bangkok's northern, eastern, and western districts were flooded, in some places for over two months.

Bangkok's geology also makes its tall buildings vulnerable to powerful earthquakes from far away, despite not being in a seismically active area, as the clay layer has an amplifying effect on [[long-period ground motion]], which tends to match the [[resonant frequency]] of high-rises. Occupants of skyscrapers in Bangkok have often felt effects from earthquakes centred hundreds of kilometres away in [[northern Thailand]] and Myanmar. Seismic considerations were only added to the building code in 2007, making older structures particularly at risk.<ref>{{cite news |last1=Kelly |first1=Shawn |title=Bangkok's tall buildings sitting on soft, shaky ground |url=https://www.nationthailand.com/perspective/30234105 |access-date=29 March 2025 |work=The Nation |date=20 May 2014}} <br />{{cite conference |last1=Warnitchai |first1=Pennung |first2=Chanet |last2=Sangarayakul |first3=Scott A. |last3=Ashford |title=Seismic hazard in Bangkok due to long-distance earthquakes |book-title=Proceedings of the 12th World Conference on Earthquake Engineering, Auckland, New Zealand |volume=30 |date=2000 |url=https://www.iitk.ac.in/nicee/wcee/article/2145.pdf}} <br />{{cite web |title=แผ่นดินไหว…ไม่ไกลคนกรุง |url=https://researchcafe.tsri.or.th/bangkok-earthquake/ |website=Thailand Science Research and Innovation |access-date=29 March 2025 |language=th |date=16 April 2020}}</ref>

[[File:Bangkok, Thailand Population Density and Low Elevation Coastal Zones (5457306973).jpg|thumb|Bangkok population density and low elevation coastal zones. Bangkok is especially vulnerable to [[sea level rise]].]]
Its coastal location makes Bangkok particularly vulnerable to [[rising sea level]]s due to [[global warming]] and climate change. A study by the [[OECD]] has estimated that 5.138&nbsp;million people in Bangkok may be exposed to [[coastal flooding]] by 2070, the seventh highest figure among the world's port cities.<ref>{{cite journal|last1=Nicholls |first1= R. J. |first2= S. |last2= Hanson |first3= C. |last3= Herweijer |first4=N. |last4= Patmore |first5=S. |last5=Hallegatte |first6= J. |last6=CorfeeMorlot |first7=Jean |last7= Chateau |first8=Robert |last8=Muir-Wood |display-authors= 3 |year=2008|title= Ranking Port Cities with High Exposure and Vulnerability to Climate Extremes: Exposure Estimates| journal= OECD Environment Working Papers|issue=1 |doi= 10.1787/011766488208|url=http://www.oecd-ilibrary.org/docserver/download/5kzssgshj742.pdf?expires=1443516109&id=id&accname=guest&checksum=86F9E81D60F674BDFA259B0843C4A964 |access-date=22 May 2014}}</ref>{{RP|8}} There are fears that the city may be submerged by 2030.<ref>{{cite web |url=http://edition.cnn.com/2007/TECH/science/10/22/thailand.water.rising.ap/index.html |title=Rising seas, sinking land threaten Thai capital |website=CNN.com |access-date=24 October 2007|archive-url=https://web.archive.org/web/20071030034936/http://edition.cnn.com/2007/TECH/science/10/22/thailand.water.rising.ap/index.html|archive-date=30 October 2007|url-status = dead}}</ref><ref>{{cite news|url=http://www.time.com/time/world/article/0,8599,2084358,00.html|archive-url=https://web.archive.org/web/20110721214027/http://www.time.com/time/world/article/0,8599,2084358,00.html|archive-date=21 July 2011|title=Thailand, Sinking: Parts of Bangkok Could Be Underwater in 2030|first=Bruno|last= Philip| magazine=Time|date=21 July 2011}}</ref><ref>{{cite news|last1=Sattaburuth|first1=Aekarach|title=Bangkok 'could be submerged in 15 years'|url=http://www.bangkokpost.com/learning/learning-news/632520/bangkok-could-be-submerged-in-15-years|access-date=23 January 2017|work=Bangkok Post|date=2015-07-23}}</ref> A study published in October 2019 in ''[[Nature Communications]]'' corrected earlier models of coastal elevations<ref>{{cite book |title=Climate Risks and Adaptation in Asian Coastal Megacities |date=September 2010 |publisher=The World Bank |location= Washington DC |pages=23–31 |chapter-url=https://siteresources.worldbank.org/EASTASIAPACIFICEXT/Resources/226300-1287600424406/coastal_megacities_fullreport.pdf |access-date=1 November 2019 |chapter=3. Estimating Flood Impacts and Vulnerabilities in Coastal Cities |archive-date=1 July 2017 |archive-url=https://web.archive.org/web/20170701082644/http://siteresources.worldbank.org/EASTASIAPACIFICEXT/Resources/226300-1287600424406/coastal_megacities_fullreport.pdf |url-status=live }}</ref> and concluded that up to 12&nbsp;million Thais—mostly in the greater Bangkok metropolitan area—face the prospect of annual flooding events.<ref name="NC-20191029">{{cite journal |last1=Kulp |first1=Scott A |last2=Strauss |first2=Benjamin H |title=New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding |journal= Nature Communications |date=29 October 2019 |volume=10 |issue=1 |pages=5752 |url= |doi=10.1038/s41467-019-13552-0|pmid= 31831733 |pmc=6908705 }}</ref><ref name="BBC-20191030">{{cite news |last1= Amos |first1=Jonathan |title= Climate change: Sea level rise to affect 'three times more people' |url=https://www.bbc.com/news/science-environment-50236882 |access-date=1 November 2019 |work=BBC |date=30 October 2019 |archive-date=6 January 2020 |archive-url=https://web.archive.org/web/20200106151232/https://www.bbc.com/news/science-environment-50236882 |url-status=live }}</ref> This is compounded by coastal erosion, which is an issue in the gulf coastal area, a small length of which lies within Bangkok's [[Bang Khun Thian District]]. Tidal flat ecosystems existed on the coast; however, many have been reclaimed for agriculture, aquaculture, and salt works.<ref>{{cite journal |last1=Murray |first1=N.J. |last2= Clemens |first2=R.S. |last3=Phinn |first3=S.R. |last4=Possingham |first4=H.P. |last5=Fuller |first5=R.A. |title=Tracking the rapid loss of tidal wetlands in the Yellow Sea |journal=Frontiers in Ecology and the Environment |date=2014 |volume=12 |issue= 5 |pages=267–272 |doi= 10.1890/130260 |bibcode=2014FrEE...12..267M |url=https://researchonline.jcu.edu.au/60169/1/130260.pdf |access-date=29 October 2021 |archive-date=7 December 2021 |archive-url=https://web.archive.org/web/20211207073933/https://researchonline.jcu.edu.au/60169/1/130260.pdf |url-status=live }}</ref>

The closest mountain range to Bangkok is the [[Khao Khiao Massif]], about {{convert|40|km|0|abbr=on}} southeast of the city. Phu Khao Thong, the only hill in the metropolitan area, originated with a very large [[stupa|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'' ({{lang|th|ภูเขา}}), as if it were a natural feature.<ref>[http://dlxs.library.cornell.edu/cgi/t/text/pageviewer-idx?c=sea;cc=sea;sid=fd258f1374ff0bf467cbfbf937e68f4e;rgn=full%20text;idno=sea141;view=image;seq=14 Old photo (around 1900) of dilapidated prang from the collection of Cornell University Library] {{Webarchive|url=https://web.archive.org/web/20150904061247/http://dlxs.library.cornell.edu/cgi/t/text/pageviewer-idx?c=sea;cc=sea;sid=fd258f1374ff0bf467cbfbf937e68f4e;rgn=full%20text;idno=sea141;view=image;seq=14 |date=4 September 2015 }} (last access 2009-09-24).</ref> In the 1940s, enclosing concrete walls were added to stop the hill from eroding.<ref>{{cite web|url=http://wikimapia.org/11129/Temple-of-the-Golden-Mount-or-Phu-Khao-Thong-%E0%B8%A0%E0%B8%B9%E0%B9%80%E0%B8%82%E0%B8%B2%E0%B8%97%E0%B8%AD%E0%B8%87|title=Phu Khao Thong (Golden Mount)|website= wikimapia.org|access-date=14 June 2014|archive-date=10 December 2008|archive-url=https://web.archive.org/web/20081210031643/http://wikimapia.org/11129/Temple-of-the-Golden-Mount-or-Phu-Khao-Thong-%E0%B8%A0%E0%B8%B9%E0%B9%80%E0%B8%82%E0%B8%B2%E0%B8%97%E0%B8%AD%E0%B8%87|url-status= live}}</ref>
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