:Subansiri Lower Dam
{{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 = Subansiri Lower Dam Geruka mukh Lakhimpur Assam.jpg
| image_size =
| image_caption = Lower Subansiri Dam, 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 = 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}}{{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}}
| 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 MW}} 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 North Eastern India. It is located {{convert|2.3|km|abbr=on}} upstream of Subansiri River in 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. The project has experienced several problems during construction to include landslides, re-design and opposition.
By early 2019, work had stalled on both of the two major dam projects in the Assam region, the Dibang and the Lower Subansiri.{{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=November 28, 2018 }}{{Dead link|date=November 2023 |bot=InternetArchiveBot |fix-attempted=yes }} The project construction resumed from October 15, 2019, after the clearance by National Green Tribunal.{{Cite web |date=30 June 2023 |title=Subansiri Lower Hydroelectric Project Achieves Construction of Dam till Top Level |url=https://www.pib.gov.in/PressReleaseIframePage.aspx?PRID=1936491 |access-date=4 March 2024 |website=Press Information Bureau: Government of India}} The remaining work of radial gates was expected to be completed after the monsoon season and electricity generation was expected to begin by the end of Financial Year 2023-24.
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|210|m|abbr=on}} from the deepest 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 powerhouse, located on the right bank, will contain eight 250 MW Francis turbine generators using 86 m design head out of 91 m gross head available.{{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}}
There will be eight horse shoe shaped 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 tunnels, 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 penstocks with varying diameters of {{convert|7|-|9.5|m|abbr=on}} and lengths of{{convert|168|-|190|m|abbr=on}}. The 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.
When complete, the hydroelectric generators will begin generating 500 MW of electricity, gradually increasing to 2000 MW. {{cite web |last=Sarmah |first=Nitish |date=Aug 31, 2021 |title=Assam: Subansiri Dam To Generate Power Soon, Opposing Bodies Cry Foul |url=https://www.guwahatiplus.com/assam/assam-subansiri-dam-to-generate-power-soon-opposing-bodies-cry-foul |website=guhahatiplus}}
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.{{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}}
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 cofferdams 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.
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.
{{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
}}
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.{{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}}
By mid-2023, the elevation of the dam had reached 210m above sea level.{{Cite web |title=Subansiri Lower Hydroelectric Project Achieves Construction of Dam till Top Level |url=https://www.pib.gov.in/www.pib.gov.in/Pressreleaseshare.aspx?PRID=1936491 |access-date=2024-04-11 |website=www.pib.gov.in}}
In October 2023, another landslide impacted construction, as part of a hill collapsed into the reservoir, blocking a tunnel and stopping water flowing into the Subansiri river.{{Cite web |date=2023-11-08 |title=How ignored landslide warnings led to Subansiri running dry |url=https://indianexpress.com/article/explained/how-ignored-landslide-warning-led-to-subansiri-river-running-dry-explained-9018295/ |access-date=2024-04-11 |website=The Indian Express |language=en}}
Environmental impact
Some 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 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 elephant corridor and some subsistence agriculture fields.{{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=October–December 2004
|archive-date=4 March 2016
|archive-url=https://web.archive.org/web/20160304040901/http://www.sandrp.in/drp/oct_nov_dec04.pdf
|url-status=dead
}}
Thirty eight families will be displaced if the dam is completed, according to official data.
{{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
}}
;Downstream
Water flow downstream will be regulated by the dam which is expected to result in low releases (6 m3/s) during winter and very high releases (2,560 m3/s) when energy is being generated.{{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
|archive-date=3 March 2012
|archive-url=https://web.archive.org/web/20120303053338/http://peakwater.org/tag/subansiri-dam/
|url-status=dead
}}
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.
References
{{reflist}}
{{Power Plants of North-east India}}
Category:Dams in Arunachal Pradesh
Category:Dams under construction