Raunak Shankhwar at 05:54, 25 March 2026

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{{Short description|Dam in Assam and Arunachal Pradesh}}{{update|updated=2014|date=April 2021}}
{{EngvarB|date=January 2014}}
{{Use dmy dates|date=January 2014}}
{{Infobox dam
| name = Subansiri Lower Project
| name_official = Subansiri Lower Hydroelectric Power Project (LSHEP)
| image = Arunachal Pradesh Lower Subansiri district locator map.svg
| image_size =
| image_caption = Location of Lower Subansiri District, Arunachal Pradesh, and Assam Northeast India
| image_alt =
| location_map = India
| location_map_size =
| location_map_caption = Location of the Subansiri Lower Dam in Arunachal Pradesh and Assam
| coordinates = {{coord|27|33|13|N|94|15|31|E|type:landmark|display=inline,title}}
| country = India
| location = Arunachal Pradesh
| status = UC
| construction_began = December 2007
| opening =
| demolished =
| cost = Rs. 62.9 billion (December 2002 est.)
| owner = [[NHPC Limited]]
| dam_type = Concrete gravity
| dam_height = {{Convert|116|m|ft|0|abbr=on}}
| dam_height_thalweg =
| dam_height_foundation= {{Convert|130|m|ft|0|abbr=on}}
| dam_length = {{Convert|284|m|ft|0|abbr=on}}
| dam_width_crest =
| dam_width_base =
| dam_volume = {{Convert|2250000|m3|cuyd|0|abbr=on}}
| dam_elevation_crest =
| dam_crosses = Lower [[Subansiri River]]
| spillway_count =
| spillway_type = [[Spillway#Energy dissipation|Ski jump]]
| spillway_capacity = {{Convert|37500|m3/s|ft3/s|0|abbr=on}}
| res_name =
| res_capacity_total = {{Convert|1.37|km3|acre.ft|0|abbr=on|lk=out}}
| res_capacity_active = {{Convert|0.44|km3|acre.ft|0|abbr=on|lk=out}}
| res_capacity_inactive=
| res_catchment =
| res_surface = {{Convert|33.5|km2|sqmi|0|abbr=on}}<ref name=register>{{cite web|title=India: National Register of Large Dams 2009|url=http://www.cwc.nic.in/main/downloads/National%20Register%20of%20Large%20Dams%202009.pdf|publisher=Central Water Commission|accessdate=10 July 2011|url-status=dead|archiveurl=https://web.archive.org/web/20110721165130/http://www.cwc.nic.in/main/downloads/National%20Register%20of%20Large%20Dams%202009.pdf|archivedate=21 July 2011|df=dmy-all}}</ref>
| res_elevation =
| res_max_depth =
| res_max_length =
| res_max_width =
| res_tidal_range =
| plant_operator = [[NHPC Limited]]
| plant_commission = 2016-2018 (est.)
| plant_decommission =
| plant_type =
| plant_turbines = {{nowrap|8 × 250 [[megawatt|MW]]}} [[Francis turbine|Francis-type]]
| plant_capacity = 2,000 MW (max. planned)
| plant_annual_gen = 7,421 GW·h
| website = [http://www.nhpcindia.com/Projects/English/Scripts/Prj_Introduction.aspx?Vid=23 Subansari (Lower) Project]
| extra =
}}
The '''Subansiri Lower Dam''', officially named '''Subansiri Lower Hydroelectric Project''' (SLHEP), is an under construction [[gravity dam]] on the [[Subansiri River]] in NorthEastern India. It is located {{convert|2.3|km|abbr=on}} upstream of Subansiri River on Arunachal Pradesh. Described as a [[run-of-the-river]] project by [[NHPC Limited]], the Project is expected to supply 2,000 MW of power when completed.<ref name=NHPCIndia/> The project has experienced several problems during construction to include landslides, re-design and opposition. It was expected to be complete in 2018. It is notable that, if completed as planned, it will be the largest hydroelectric project in India.<ref name="TNN">
{{cite web|url=http://articles.timesofindia.indiatimes.com/2012-02-16/guwahati/31066360_1_subansiri-dam-lower-subansiri-nhpc-officials|archive-url=https://web.archive.org/web/20131214120044/http://articles.timesofindia.indiatimes.com/2012-02-16/guwahati/31066360_1_subansiri-dam-lower-subansiri-nhpc-officials|url-status=dead|archive-date=14 December 2013|title=Construction of Subansiri dam not to be stopped|accessdate=9 March 2012|work=[[The Times of India]]|date=16 February 2012}}</ref><ref name="AT">{{cite web|title=Subansiri dam work not to be halted: Ramesh|url=http://www.assamtribune.com/scripts/detailsnew.asp?id=aug1310/at07|publisher=The Assam Tribune|accessdate=28 August 2010|date=12 August 2010}}</ref>

As of early 2019, work was not progressing on either of the two major dam projects in the Assam region, the [[Dibang Dam|Dibang]] and the Lower Subansiri.<ref name="ncAssam">{{cite news |last1=Talukdar |first1=Sandipan |title=Big Dams in Arunachal likely to Resume Work after NGT Green Signal |url=https://www.newsclick.in/big-dams-arunachal-likely-resume-work-after-ngt-green-signal |accessdate=27 December 2018 |publisher=NewsClick |date=Nov 28, 2018}}</ref>

After clearance of ‘Subansiri Lower Project’ by Hon’ble NGT vide its Order dated: 31.07.2019, Main works of the Dam has been resumed on 15.10.2019.

==Design==
{{Infobox bridge
| name = Subansiri Lower Dam bridge
| carries = vehicles
| width = {{Convert|150|m|ft|0|abbr=on}}
| length = {{Convert|150|m|ft|0|abbr=on}}
}}
The concrete [[gravity dam]] is designed to be {{convert|116|m|abbr=on}} tall, measured from the river bed and{{convert|130|m|abbr=on}} from foundation. Its length will be {{Convert|284|m|ft|0|abbr=on}} and the dam will have a structural volume of {{Convert|2250000|m3|cuyd|0|abbr=on}}. The reservoir created by the dam will have a gross storage capacity of {{Convert|1.37|km3|acre.ft|0|abbr=on|lk=out}}, of which {{Convert|.44|km3|acre.ft|0|abbr=on|lk=out}} can be used for power generation or irrigation. At normal level, the reservoir's surface will cover {{Convert|33.5|km2|sqmi|0|abbr=on}}. The surface [[power station|powerhouse]], located on the left bank, will contain eight 250 MW [[Francis turbine]] generators.<ref name=register/><ref name=NHPCIndia>{{cite web|title=Welcome to Subansiri (Lower) Project|url=http://www.nhpcindia.com/Projects/english/Scripts/Prj_Introduction.aspx?Vid=23|publisher=NHPC India|accessdate=12 March 2012}}</ref>

There will be eight horse shoe shaped [[Tailrace#Headrace.2C tailrace|head race]] tunnels, each being {{convert|9.5|m|abbr=on}} in diameter and having a length from {{convert|608|-|1168|m|abbr=on}}. There will be eight horse Shoe shaped [[surge tunnel]]s, each being {{convert|9.5|m|abbr=on}} in diameter and having length from {{convert|400|-|485|m|abbr=on}}. There will be eight horse shoe/circular shaped [[penstock]]s with varying diameters of {{convert|7|-|9.5|m|abbr=on}} and lengths of{{convert|168|-|190|m|abbr=on}}. The [[Tailrace#Headrace.2C tailrace|tail race]] channel, which will transfer water discharged by the turbines back to the river, is {{convert|206|m|abbr=on}} wide and {{convert|35|m|abbr=on}} long.<ref name=NHPCIndia/>

==Construction==
Construction of Subansiri Lower Project involves many challenges. These include land not being available when construction was scheduled to commence, a limited annual construction time because of monsoons (from mid-April to mid-October), the need to handle high flood flows and poor rock conditions. The design of the dam has undergone drastic and repeated revisions that have affected the schedule and planning of the construction work.<ref name="HW">{{cite web|url=http://www.hydroworld.com/index/display/article-display/9303458802/articles/hydro-review-worldwide/Vol-20/issue-1/articles/dam-design/Planning-and-Building.html|title=Planning and Building the Subansiri Lower Dam and Hydro Project|author= Biswajit Das|publisher=PennWell Corporation|accessdate=7 March 2012|work=HydroWorld|year=2011}}</ref>

In December 2003 the contract to build the dam and its associated structures was awarded to a consortium of Boguchandgesstroy, Soyuzgidrosptsstry and Soma Enterprise Ltd. Due to difficulties acquiring land around the site, construction could not begin in earnest until 13 months after the contract was awarded. Unexpected geological conditions at the dam site led to landslides and slower tunnel excavation. By November 2007, the river was successfully diverted and in April of the next year, the foundation was clear for construction. Before the foundation was fully prepared it was discovered that bedrock was reached {{Convert|10|m|ft|0|abbr=on}} sooner than expected. This led to an alteration in the dam's design for stability. While the dam was being re-designed, concrete was placed over the foundation to protect it from the upcoming monsoon floods as the [[cofferdam]]s stood a good chance of not protecting the foundation from the strong floods. The re-design was completed in October 2008 and soon after the foundation was once again cleared. In May 2009, work was suspended because of the monsoon season and re-commenced in November of that year.<ref name="HW"/>

As of November 2011, the dam reached an elevation of {{convert|138|m|abbr=on}}, just below the spillway elevation of {{convert|145|m|abbr=on}}. On 16 December 2011, construction equipment was halted by protests.<ref name="CD">
{{cite web
|url=http://www.chinadialogue.net/article/show/single/en/4799
|title=Fighting India's mega dams
|author=Tanmoy Sharma
|publisher=China Dialogue
|accessdate=7 March 2012
|work=The Third Pole
}}</ref>

The construction cost has gone up by about {{INR}}1,200 crore owing to forced suspension of work since December 2011. NHPC has already spent about {{INR}}6,600 crore, according to a status report prepared by the company.<ref name="bp">{{cite web|title=Subansiri Project dispute to be resolved through negotiations|url=http://news.biharprabha.com/2014/07/subansiri-project-dispute-to-be-resolved-through-negotiations/|work=IANS|publisher=news.biharprabha.com|accessdate=6 July 2014}}</ref>

Commissioning of the first generator is loosely expected to occur in 2016 with the final generator in 2018.<ref>{{cite web | url=http://www.cea.nic.in/reports/proj_mon/status_he_execution.pdf | title=Status of Hydro Electric Projects under Execution for 12th Plan & beyond | publisher=Central Electric Authority - India | date=31 March 2014 | accessdate=9 July 2014 | url-status=dead | archiveurl=https://web.archive.org/web/20140715003433/http://www.cea.nic.in/reports/proj_mon/status_he_execution.pdf | archivedate=15 July 2014 | df=dmy-all }}</ref>

==Environmental impact==
Some [[environmental impact of reservoirs|environmental impacts]] unique to very large dams will result from completion of the Subansiri Project, both upstream and downstream of the dam site. These impacts will include [[Hydroelectricity#Ecosystem damage though nominal and loss of land|ecosystem damage and loss of land]].

The reservoir of the Subansiri Project will submerge a {{convert|47|km|abbr=on}} length of the Subansiri river and occupy {{convert|37.5|-|40|km2|abbr=on}} which includes [[Himalayan subtropical pine forests]], [[Himalayan subtropical broadleaf forests]], part of the Tale Valley Wildlife Sanctuary, an [[wildlife corridor|elephant corridor]] and some [[subsistence agriculture]] fields.<ref name="DRP">
{{cite journal
|url=http://www.sandrp.in/drp/oct_nov_dec04.pdf
|title=Lower Subansiri: NHPC had to pay Rs 3 B for forestland
|publisher=SANDRP
|accessdate=9 March 2012
|journal= Dams, Rivers & People
|volume= 2-issue 9-10-11
|page=12
|date=Oct, Nov, Dec 2004
}}</ref>

Thirty eight families will be displaced if the dam is completed, according to official data.<ref name="DV">
{{cite book
|url=https://books.google.com/books?id=0t_CU9gmi8cC&q=Subansiri+dam+submerge+km2&pg=PA323
|title=The Indigenous World 2004
|author= Diana Vinding
|publisher=Eks-Skolens Trykkeri
|issn=0105-4503
|isbn= 87-90730-83-6
|location= Copenhagen
|accessdate=9 March 2012
|page=323
|year=2004
}}</ref>
;Downstream
Water flow downstream will be regulated by the dam which is expected to result in low releases (6 m<sup>3</sup>/s) during winter and very high releases (2,560 m<sup>3</sup>/s) when energy is being generated.<ref name="PW">
{{cite web
|url=http://peakwater.org/tag/subansiri-dam/
|title=People's Power Blocks Dam Construction in Northeast India
|publisher=Peakwater
|accessdate=9 March 2012
|work= Tag Archive for 'Subansiri Dam'
|date=5 December 2011
}}</ref>

The project has met stiff resistance from several groups including [[All Assam Students’ Union]] and the [[Krishak Mukti Sangram Samiti]], who are apprehensive about safety and the project’s downstream impact.<ref name="bp"/>

==References==
{{reflist}}

{{Power Plants of North-east India}}

[[Category:Dams in Arunachal Pradesh]]
[[Category:Dams in Assam]]
[[Category:Dams under construction]]
[[Category:Dams in the Brahmaputra River Basin]]
[[Category:Proposed infrastructure in India]]

Subansiri Lower Dam - Revision history

Raunak Shankhwar at 05:54, 25 March 2026

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