List of bridges in Bhutan

Cantilever beams were developed in order to cross increasingly wide streams or rivers, where simple wooden beams had a limited range of about 10 meters. Two arms with timber superimposed are built on either side of the river, above the highest flood-level point, while being weighted to allow an increasingly large cantilevering, and solid wooden beams are then fixed on each end of the arms with wooden pegs. Bridges of this type were very common in mountainous region of India, Nepal and Tibet with an average span of 20 metres (66 ft), but those from bhutan have the particularity of being more elaborate with stone masonry bridge towers, roofed with wooden shingles above the abutments or bridge head structures.[1][2] The main purpose of these towers was to act as a counterweight to stiffen the structure.[3]

A traditional suspension bridge in the foreground and a modern one in the background

The use of more layers of wooden beams with more pronounced inclinations permit to achieve greater spans, one of the most significant example is the Wangdue Zam with a span reported from 112 to 180 feet (34.1 to 54.9 m) according to different sources.[4][5][6] The renovation of the Punakha Bridge in the city of the same name in 2008 by a swiss company[7] made it possible with this technique to reach a span of 55 metres (180 ft), the largest for this type of bridge in Bhutan.

All these bridges are called Bazam, a word composed of Ba which means Cattle and Zam who is the traduction of Bridge in Dzongkha, the national language of Bhutan. This comes from the resemblance of the cantilever beams that sit opposite each other with two noses of cattle.[8]

A major innovation was created by Thang Tong Gyalpo regarding the crossing of large spans, he developed iron chains working techniques and adapted them to the construction of bridges. By adding arsenic to the iron (a bit more than 2.8%),[9] it was easier to work with and had good resistance against rust, some of these chains are still functional today. This made it possible to reach spans to over a hundred meters which had not yet been reached in Europe at this time, the Chushul Chakzam in Tibet is reported to be 150 yards (140 m) long.[4]

After making more than a hundred such bridges in Tibet, Thang Tong Gyalpo came to Bhutan in 1433 where he found big iron ore deposits and locals blacksmiths, many chains forged here were shipped from Bhutan to Tibet.[10] He build 8 bridges in the country, oftentime near ore deposits, and some of them were still in use in the 20ht century, the last existing bridges are Tamchog Chakzam, Doksum Chakzam, Dangme Chakzam, and Khoma Chakzam[11] (Chakzam literally means "iron bridge" in standard Tibetan).

		Name	Dzongkha	Distinction	Length	Type	Carries Crosses	Opened	Location	District	Ref.
	1	Tamchog Chakzam rebuilt in 2005		Built by Thang Tong Gyalpo		Suspension Chain bridge, masonry towers	Footbridge Paro Chhu	1433	Tamchog Lhakhang 27°19′46.7″N 89°30′16.7″E	Paro District	[Note 1] [10] [12]
	2	Punakha Bridge rebuilt in 2008	Puna Mochhu Bazam	Span : 55 m (180 ft) Punakha Dzong	73 m (240 ft)	Covered bridge Cantilever wooden beam, 2 masonry towers	Footbridge Mo Chhu	1637	Punakha 27°34′59.8″N 89°51′42.4″E	Punakha District	[Note 2] [S 1] [13] [14]
	3	Nemi Zam		Rinpung Dzong	24 m (79 ft)	Covered bridge Cantilever wooden beam, 2 masonry towers	Footbridge Paro Chhu	18th century	Paro 27°25′29.1″N 89°25′18.7″E	Paro District	[Note 3] [15]
	4	Wangdue Zam destroyed in 1968		Constructed without using single piece of iron § Wangdue Phodrang Dzong		Covered bridge Cantilever wooden beam, 3 masonry towers	Footbridge Sankosh River	18th century	Wangdue Phodrang 27°28′29.1″N 89°53′42.7″E	Wangdue Phodrang District	[Note 4] [3] [5] [16]
	5	Dotanang Covered Bridge			46 m (151 ft)	Covered bridge Cantilever wooden beam, 2 masonry towers	Footbridge Raidāk River (Wang Chhu)	19th century	Dotanang 27°35′37.0″N 89°37′45.1″E	Thimphu District	[15]
	6	Kuendeyling Baazam				Covered bridge Cantilever wooden beam, 2 masonry towers	Footbridge Raidāk River (Wang Chhu)		Thimphu 27°28′30.4″N 89°38′32.3″E	Thimphu District
	7	Langjo Bridge		Tashichho Dzong		Covered bridge Cantilever wooden beam, 2 masonry towers	Footbridge Raidāk River (Wang Chhu)		Thimphu 27°29′30.7″N 89°38′09.0″E	Thimphu District	[Note 5] [6]
	8	Changjiji Bridge			29 m (95 ft)	Covered bridge Cantilever wooden beam, 2 masonry towers	Footbridge Raidāk River (Wang Chhu)	2007	Thimphu 27°27′22.4″N 89°38′56.2″E	Thimphu District	[Note 6] [8] [18]
	9	Punakha Suspension Bridge				Suspension Steel	Footbridge Pho Chhu		Punakha 27°35′20.3″N 89°52′11.8″E	Punakha District	[S 2]

This table presents the structures with spans greater than 100 metres (330 ft) (non-exhaustive list).

		Name	Dzongkha	Span	Length	Type	Carries Crosses	Opened	Location	District	Ref.
	1	Amochhu Bridge			175 m (574 ft)	Arch Steel through arch	Road bridge Torsa River	2018	Phuntsholing 26°53′10.1″N 89°20′06.4″E	Chukha District Samtse District	[19] [20]
	2	Diana Kuephen Bridge			320 m (1,050 ft)	Suspension Steel truss deck, steel pylons	Road bridge Samtse–Sipsu road	2003	Samtse 26°55′37.1″N 89°02′34.1″E	Samtse District	[21]
	3	Panbang Bridge			152 m (499 ft)	Arch Steel through arch	Road bridge Manas River	2013	Panbang 26°51′10.3″N 90°57′41.3″E	Zhemgang District	[22]

• Transport in Bhutan
• Geography of Bhutan
• List of rivers of Bhutan
• Architecture of Bhutan

• Notes

• Nicolas Janberg. "International Database for Civil and Structural Engineering". Structurae.com.

• Others references

• Aris, Michael (1982). Views of Medieval Bhutan, The Diary and Drawings of Samuel Davis - 1783. Washington D.C.: Smithsonian Institution Press. ISBN 0-87474-210-2.
• Deloche, Jean (1984). The Ancient Bridges of India. New Delhi: Sitaram Bhartia Institute of Scientific Research.
• Gerard, Alexander (1841). Account of Koonawur in the Himalaya, Etc. ... London: James Madden.
• Gerner, Manfred (2007). Thangtong Gyalpo: Architect, Philosopher and Iron Chain Bridge Builder (PDF). ISBN 978-99936-14-39-5. {{cite book}}: |website= ignored (help)
• Kalmus, Marek (November 2015). "Remarks on selected bridges of Thangtong Gyalpo". Journal of Comparative Cultural Studies in Architecture. ResearchGate (Report). pp. 20–32.
• Stearns, Cyrus (2007). King of the Empty Plain: The Tibetan Iron Bridge Builder Tangtong Gyalpo. Boston: Shambhala Publications. ISBN 978-1-5593-9837-4.
• Turner, Samuel (1800). An Account of an Embassy to the Court of the Teshoo Lama in Tibet: Containing a Narrative of a Journey Through Bootan, and Part of Tibet. London: W. Bulmer and Co.

• "Des Ponts couverts en Asie" [Covered Bridges in Asia]. Timbresponts.fr (in French).
• "Stamps On Bridges of Bhutan". Bhutanphilately.blogspot.fr. July 8, 2010.
• "Bridges Map of Wangdue Phodrang District - scale :1:300 000" (PDF). Nsb.gov.bt - National Statistics Bureau. Archived from the original (PDF) on November 16, 2020.
• "Bridges table of Wangdue Phodrang District". Nsb.gov.bt - National Statistics Bureau. Archived from the original (xls) on November 16, 2020.
• Rosenberg, Katrin (August 2009). Good Governance in Bridge Building, Suspension Bridge Programme - Sharing Experiences from Bhutan. Helvetas Bhutan.
• Data collection survey on road connectivity in the Kingdom of Bhutan (PDF). Openjicareport.jica.go.jp - Japan International Cooperation Agency (Report). September 2014.
• "Arch Bridges - Bhutan". Yokogawa-bridge.co.jp.