Main features of the Nam Theun 2 hydroelectric project ... · Main features of the Nam Theun 2 hydroelectric project (Lao PDR) and the associated environmental monitoring programmes

Hydroécol. Appl.© EDF, 2014DOI: 10.1051/hydro/2014005

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Main features of the Nam Theun 2 hydroelectricproject (Lao PDR) and the associated environmentalmonitoring programmes

Principales caractéristiques de l’aménagementhydroélectrique de Nam Theun 2 (Laos) et programmesde suivi environnementaux

Stéphane Descloux(1), Pierre Guedant(2), Dousith Phommachanh(3),

Ruedi Luthi(4)

(1) EDF – Hydro Engineering Centre, Sustainable Development Department, Savoie-Technolac,73373 Le Bourget-du-Lac, [email protected]

(2) Nam Theun 2 Power Company Limited (NTPC), Environment & Social Division – Water Quality andBiodiversity Dept.– Gnommalath Office, PO Box 5862, Vientiane, Lao PDR

(3) NTPC - Operation & Maintenance Division – Operation Dept.– Gnommalath Office, PO Box 5862, Vientiane,Lao PDR

(4) NTPC - Environment & Social Division – Gnommalath Office, PO Box 5862, Vientiane, Lao PDR

Abstract – The Nam Theun 2 hydroelectric Project is located in Lao PDR on the Nam TheunRiver. The reservoir impoundment started in April 2008 and hydropower generation beganin March 2010. The reservoir has a total volume of 3.9 billion m3, covering an area of 489 km2

at full supply level and 86 km2 at the minimum operating level. The performance is 1070 MWand the annual production is 6 TWh. The reservoir is operated seasonally by storing waterduring the wet season. A system of tunnels and channels diverts the waters from the NamTheun watershed to the Xe Bangfai watershed. An ambitious environmental monitoring pro-gramme of project sites was launched by EDF - NTPC in 2008 and remains operational. Anon-site laboratory was established to ensure sampling and analysis in real time. The com-partments studied are water quality, greenhouse gas emissions, phytoplankton, zooplankton,benthic macroinvertebrates and fish. A 3D numerical model was developed based on moni-toring data to predict the long-term changes in water quality and greenhouse gas productionof the reservoir. Additional research programmes have been launched to understand bio-che-mical dynamics and processes.

Key words – Nam Theun 2, dam, sub-tropical reservoir, impoundment, environmentalmonitoring

Résumé – Le projet hydroélectrique de Nam Theun 2 se situe au Laos sur la rivière NamTheun. Le réservoir a été mis en eau en avril 2008 et la production hydroélectrique a com-mencé en mars 2010. Il couvre une superficie totale de 489 km2 à la cote maximale et 86 km2

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2 S. Descloux et al.

à la cote minimale d’exploitation. Le volume total du réservoir est de 3,9 milliard de m3. Lapuissance totale est de 1070 MW pour un productible de 6 TWh. L’aménagement est géréde façon saisonnière en stockant les eaux pendant la saison humide. Il dérive les eaux dela Nam Theun vers le bassin versant de la Xe Bangfai. Un programme ambitieux de suivi deseffets sur l’environnement a été conduit par EDF et NTPC dès 2008. Toujours en activité, ceprogramme a nécessité la mise en place d’un laboratoire sur site pour assurer les prélève-ments et analyses en temps réel. Les compartiments étudiés sont la qualité des eaux, lesgaz à effet de serre, le phytoplancton et le zooplancton, les macro-invertébrés benthiques etles poissons. Un modèle numérique 3D a également été élaboré à partir des données du suiviafin de prévoir l’évolution du réservoir en termes de qualité des eaux et de production de gazà effet de serre. Des programmes de recherche complémentaires ont été lancés en parallèleafin d’apporter des éléments de réponses à certains problèmes spécifiques.

Mots-clés – Nam Theun 2, barrage, réservoir sub-tropical, mise en eau, suivienvironnemental

1 INTRODUCTION

Southeast Asian economies aredeveloping fast and large parts of thegrowing electricity demand will besourced by hydropower. The Mekongwatershed was identified for numeroushydropower projects. Among the coun-tries surrounding the Mekong basin,the Lao People’s Democratic Republic(Lao PDR) harbours a high hydro-power potential.

The hydroelectric potential of theNam Theun River on the Nakai Plateauwas for the first time mentioned in 1927.In 1994, the Nam Theun 2 ElectricityConsortium (NTEC) was created toplan and design the Nam Theun 2(NT2) Project. It included a comprehen-sive environmental and social impactassessment and was supported by theWorld Bank, the Agence Française deDéveloppement, the Asian Develop-ment Bank and the Government ofLaos. The NT2 Project is part of the7000 MW electricity export programmebetween Laos and Thailand. By 2004,

NTEC transferred the development andimplementation responsibility to thenewly founded Nam Theun 2 PowerCompany Ltd. (NTPC). NTPC is ashareholder company, owned by Elec-tricité de France International (EDFI,40%), Lao Holding State Enterprise(LHSE, 25%), Electricity GeneratingPublic Company Limited (EGCO,35%). NT2’s construction works beganin 2005 consecutive to the finalizationof the Concession Agreement (CA).The construction was completed in2009, the hydropower generation inMarch 2010 and commercial operationbegan in April 2010.

The CA defines environmental andsocial obligations, some of which lastthroughout the concession period. Theimplementation of the environmentaland social programmes is monitored byvarious external agencies including thetechnical advisors of the lending agen-cies, the Laotian Government throughthe Panel of Experts and IndependentMonitoring Agencies, independent con-sultants and multilateral development

Main features of the Nam Theun 2 hydroelectric project (Lao PDR) 3

institutions (NTPC, 2004). The socialand environmental safeguard stand-ards of the World Bank and the AsianDevelopment Bank are built into the CAto minimise and mitigate social andenvironmental impacts. By early2008, the Hydro Engineering Centreof EDF (CIH) and NTPC decided toimplement an environmental monitor-ing programme to conduct a compre-hensive study of the evolution of theaquatic ecosystem consecutive to theimpoundment of the reservoir.

The objective of this article is topresent the NT2 Project including: (i)the main features of the project, (ii) thedescription of the period from impound-ment to normal operation and (iii) theenvironmental monitoring programmeof the reservoir impoundment. This arti-cle is an introduction of a series of arti-cles included in the special issue “NT2Environmental Studies” of “Hydroécol-ogie Appliquée” that presents thechemical, biological and modellingresults of the monitoring programmeimplemented by EDF CIH and NTPC.

2 MAIN FEATURESOF THE PROJECT

2.1 Nam Theun and Xe BangfaiRivers catchments

The project area is located in thecentre of Lao PDR (KhammouaneProvince) on two sub catchments of theMekong River. It is a trans-basinproject: the reservoir is located on theNakai Plateau in the Nam Theun water-shed, while electricity generation facili-ties and water release are in the XeBangfai watershed (Figs. 1 and 2).

The project area is characterised bya sub-tropical monsoon climate withthree distinct seasons: warm-wet (Juneto October), cool-dry (November toFebruary) and warm-dry (March toMay). Most of the annual runoff occursin the wet season (around 90%).Maximum recorded precipitation was390 mm day-1 (2011) and the annualaverage rainfall was 2432 mm year-1

(1995-2013; NTPC, OMD Data). Overthe period from 1987 to 2002, the aver-age temperature recorded at the Nakaiplateau was 3 °C cooler than in theMekong valley due to the difference ofaltitude (SMEC, 2003). The meanannual temperature on the plateau is22.6 °C with an average of 33.0 °C inApril (hottest month) and an average of9.6 °C in January (coldest month).

Some average and extreme dis-charge values of the rivers, prior toconstruction, are shown in Table I. Thelowest mean daily discharge recordedin the Nam Theun River at the dam sitewas 4.4 m3 s-1 in April 1986 (SMEC,2003) and the 100 years return floodwas estimated at 6134 m3 s-1 (EDF-DTG, 2013). The Nam Theun Rivermean annual inflow is 238 m3 s-1

(Tab. I), sourced by its tributaries: NamOn, Nam Yang, Nam Noy, Nam Monand Nam Xot Rivers flowing frommountains North-East (Fig. 1). As theriver discharge is directly related to pre-cipitations, there is a high difference ofinflows between the dry and the wetseason (Tab. I). The total annual runofffrom the catchment area at the NakaiDam site is about 7526 million m3

(SMEC, 2003). The NT2 Project divertsthe water from the Nam Theun to theXe Bangfai catchment. Discharge intothe Downstream Channel and the Xe


Fig. 1. Location of the NT2 site and monitoring stations.

Fig. 1. Cartographie du site de NT2 et des stations de suivi.


Bangfai River depends on the powergeneration and ranges from 0 to333 m3 s-1. The Nam Kathang Noy andNgai flow into the Regulating Ponddownstream of the Power House and

Nam

Nam Theun 2 Reservoir

Mekong River

Nam Theun River

Nam NiamRiver

Regula�ng pond

Power sta�on

Downstream channel

Fig. 2. Hydraulic scheme of the Nam Theun and Xe

Fig. 2. Schéma hydraulique des bassins de la Nam

Table I. Characteristics of the rivers, discharges pre

Tableau I. Caractéristiques des rivières en m3 s-1 (

Stations Data series

Nam Theun at the Dam site 1950-2002

Nam Kathang at theRegulating Dam

1994-2002

Xe Bangfai at Mahaxai 1989-2002

Mekong after the confluenceof the Xe Bangfai

1922-1992

are small tributaries of the Nam GnomRiver. The latter is itself a tributary ofthe Xe Bangfai and its confluence islocated upstream of the DownstreamChannel confluence.

Phao River

Nam Theun River

Nam Noy River

Nam On River

Nam Xot River

Nam Mon River

Xe Bangfai River

Nam Kathang/ Nam Gnom

Nam Theunwatershed

Xe Bangfaiwatershed

Bangfai bassins.

Theun et de la Xe Bangfai.

sented are in m3 s-1 (NTPC, 2004).

NTPC, 2004).

Mean annualdischarge

Mean driestmonth

Mean wettestmonth

238 31.9 (Apr) 734.7 (Aug)

10.2 0.3 (Apr) 38.5 (Sept)

265.4 12.7 (Apr) 921.2 (Aug)

6960 1552 (Apr) 21453 (Aug)


2.2 Reservoir characteristics

The closure of the Nakai Dam onthe Nam Theun River led to the inunda-tion of 195 km of rivers and to the for-mation of a 489 km² reservoir, at fullsupply level, 538 m above sea level(asl) (EDF-DTG, 2012). The total stor-age capacity is of 3.9 billion m3 with anactive volume of 3.6 billion m3. AtNakai Dam, the Nam Theun watershedis about 4039 km².

The bedrock mainly consists offine to medium grained micaceous,quartzose red-brown and grey sand-stone and brown-red to brown mud-stone and siltstone. In the central areaupstream of Ban Thalang, late tertiaryalluvial deposits can be found. The NamTheun River meandered through thisarea where soils are composed of softto very stiff, silty clays and loams. Rightalong the river, more recent alluviummaterial, consisting of fine to coarsesands were present (NTPC, 2005).

The reservoir is located on theNakai Plateau where the water is cap-tured at the Intake, channelled throughthe Pressure Tunnel, the PowerHouse, the Regulating Dam and the27 km long Downstream Channel andfinally released to the Xe Bangfai Riverabout 30 km south of the Power House(Fig. 2).

The NT2 Reservoir is a narrowwater body of approximately 80 kmlong and 5 km large. The reservoir ishighly dendritic and relatively shallowwith an average depth of 8 m (maxi-mum depth of 39 m; Chanudet et al.,2012). It is characterized by a maxi-mum water level range of 12.5 m(NTPC, 2005), which results in a dras-tic reduction in the reservoir surface

area at the end of the dry season. TheNT2 Reservoir is managed on a sea-sonal basis: incoming waters arehigher than the production capacityduring the wet season and water isstored in the reservoir. During lowinflows, the installed capacity is higherthan incoming water flow and the levelof the reservoir decreases. The reser-voir surface fluctuates from 86 km² atthe minimum operating level, to 489km² at the full supply level and from525.5 m asl to 538 m asl, respectively(DTG, 2012).

The NT2 Reservoir is characterizedas a warm monomictic lake, i.e. com-pletely mixed once a year during thecool dry season (Chanudet et al.,2012). The water residence time is esti-mated to be 6 months.

Prior to impoundment, 69% of thetotal reservoir area was covered bydense, medium and light forests, 13%was covered by agriculture land andwetlands (the remaining 18% was cov-ered by degraded and riparian forests,water and roads). The mean carbondensity was estimated at 115±15 tC/ha(for a soil thickness of 30 cm), corre-sponding to a total flooded organic car-bon stock of 5.1±0.7 MtC (Desclouxet al., 2011).

The NT2 Reservoir can be dividedinto 2 zones: (i) the South-East zonewith a shallow reservoir and initiallymainly covered by agricultural soilsand swamps, receiving the main tribu-tary inflows and (ii) the North-Westzone with a higher water depth and ini-tially covered by forest. During normaloperation (after commissioning), theresidence time in this area is longerthan in the South-East zone due to lowoutflows at the Dam site.


2.3 Project design

The Nakai Dam (Figs. 1 and 2) is439 m long and 39 m high andincludes five radial gates to evacuatefloods (up to 16000 m3 s-1). The reser-voir is surrounded by 13 saddle dams(for a total length of 4.4 km) on thesouth and west side walls to close thereservoir. A riparian release (i.e. theenvironmental flow) of 2 m3 s-1 isreleased at the Nakai Dam to the NamTheun River. A multi-level off-takeallows the riparian release to be selec-tively taken from the reservoir oxygen-ated surface water. This riparianrelease is then discharged through anaeration cone valve.

The Headrace Channel is located inthe upstream zone of the reservoir(near RES9; Figs. 1 and 3). It is 4 kmlong and reaches a maximum depth of34 m at the Intake. It ensures that thereservoir water mass can reach theIntake, even when the water level in thereservoir is low. Further downstream ofthe Intake, water enters the HeadraceTunnel (1500 m in length and 9.2 m indiameter), then goes to the PressureShaft (vertical drop of 220 m, diameterof 8.8 m) and finally descends to thePressure Tunnel (1142 m in length and7.15 m in diameter; Fig. 3). There is asurge shaft of 109 m in height and8.8 m in diameter. The Power House islocated 360 m below the Nakai plateau.It shelters four "Francis" (total of 996.5MW) and two "Pelton" turbines (total of75 MW). The total performance is 1070MW and the mean production capacityis approximately 6000 GWh year-1.The ratio of flooded lands is therefore2.2 W m-2.

Downstream of the Power House,water is conveyed to a RegulatingPond through a 340 m long TailraceChannel with a 345 m3 s-1 capacity(NTPC, 2004). With a capacity of 8 mil-lion m3, the Regulating Pond buffersthe turbinated flows on a daily andweekly scale. It is closed by a dam of531 m in length (concrete dam 135 mlong and earth dam 396 m long) andreceives natural tributaries of the NamKathang River (Nam Kathang Noy andGnai). Downstream of the RegulatingPond, two outflows have been con-structed: (i) a riparian release to theNam Kathang with an outflow corre-sponding to the natural inflow (mini-mum environmental flow of 0.2 m3 s-1).The Nam Kathang flows into the NamGnom River approximately 5 km fromthe Regulating Dam, (ii) the mainrelease (water from PWH) through a27 km long Downstream Channeltowards the Xe Bangfai River (Figs. 1and 3). The Downstream Channel iscomposed of rocks and soil and canevacuate a maximum flow of 330 m3 s-1.An Aeration Weir (labyrinth type) wasbuilt in the mid zone of the Down-stream Channel to provide a maximumaeration capacity. The structureincludes a U-shaped weir constructedof reinforced concrete walls which are6 m high and approximately 160 mlong (+10 m on each side of the chan-nel), giving a total overflow crest lengthof approximately 340 m. Sub-horizon-tal perforated wooden plates areattached to the downstream edge ofthe crest to divide the flow over theweir into multiple discharges, therebymaximizing aeration. In its course, theDownstream Channel finally crosses a


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karst mountain through a 600 m longtunnel.

3 THE NT2 PROJECT SINCE 2008

3.1 Hydro-meteorological data

Atmospheric pressure is heavilycorrelated with precipitation. Pressureis low during the warm-wet season(938 + 3 hPa) and high during the cool-dry season (954 + 3 hPa; Fig. 4). Theannual hydrologic cycle is precipita-tion-driven and the peak rainfall eventwas recorded in 2011 with 390 mmday-1. The annual average rainfallsrecorded in the meteorological station

Fig. 4. Atmospheric pressure (hPa), air temperatumm day-1) at the meteorological station at Ban Tha

Fig. 4. Pression atmosphérique (hPa), températu(courbe grise en mm jour-1) à la station météorolo(2008 – 2013).

of Ban Thalang (RES4) were 2580 mm,2502 mm, 3162 mm and 2162 mmrespectively in 2009, 2010, 2011 and2012. 2009 and 2010 representedaverage rainfall years, whereas 2011was a very wet year and 2012 was avery dry year. Air humidity was highwith a mean value of 80.9% (+ 8.5%)over the study period (Air humiditymeans were 85.8 + 6.9%, 77.7 + 8.2%and 76.5 + 7.0% respectively for thewarm-wet, cool-dry and warm-dry sea-sons). Since 2008, air temperaturesranged from 12 to 30 °C with an aver-age value of 23.21 °C (Fig. 4). Windspeed is generally low throughout theyear with an average value of 1.96 +0.9 m s-1 over the study period (Fig. 5).Wind direction is also influenced by the

re (black line in °C) and precipitation (grey line inlang during the study period (2008 – 2013).

re de l’air (courbe noire en °C) et précipitationsgique de Ban Thalang pendant la période d’étude


southwest and northeast monsoon. Overthe period 2008 to 2013, maximum windspeed was recorded during the cool-dryseason (8.5 m s-1 over 10 minutes inDecember 2008) whereas the lowestvalues were recorded during thewarm-wet season.

The main natural reservoir inflowcomes from the Nam Theun River. Dailyaverage discharge (Fig. 6) was highlycorrelated with rainfall. An absence of

Fig. 5. Wind speed (m s-1) at the meteorologica(2008 – 2013).

Fig. 5. Vitesse du vent (m s-1) à la station météorol(2008 – 2013).

peak flows was observed in 2008 and2012 contrary to 2010 and 2011 wherehigh flows occurred several times ayear. The Nam Kathang River is astream with contrasting hydrologic con-ditions among seasons. For instance,the river bed can completely dry up dur-ing the dry seasons (Fig. 6). The XeBangfai River also exhibits seasonalflows; although this river did not run dryduring the study period, it had low flows

l station at Ban Thalang during the study period

ogique de Ban Thalang pendant la période d’étude


(approximately 50 m3 s-1) during the dryseason (Fig. 6).

3.2 Impoundment details andnormal operation

The first filling of the reservoirstarted in April 15th 2008 (Fig. 7). The

Fig. 6. Average daily discharges in the Nam Theun

Fig. 6. Débits moyens journaliers dans les rivières N

water level increased gradually untilNovember 2008 to 537 m as a result ofhigh inflows during the wet season.The reservoir was maintained at thislevel for 44 weeks and slowlyincreased to 538 m (full supply level) inthe second week of October 2009. Bythe end of the 2009 wet season, inflows

, Nam Kathang and Xe Bangfai Rivers (in m3 s-1).

am Theun, Nam Kathang et Xe Bangfai (en m3 s-1).


had filled up the reservoir and wereflushed between June and October2009. As shown in Figures 6 and 7,flows were spilled at the dam sitethrough the flood gates. During thisevent, outflows were slightly higherthan inflows. As a consequence, thewater level decreased and facilitatedthe flush. The objective of the ‘fill and

Fig. 7. Evolution of the reservoir water level (m) alevel of 526 to 538 m during the study period (2008reservoir at a low level (530 m asl – left picture) an

Fig. 7. Évolution du niveau d’eau du réservoir (m)du réservoir entre 526 et 538 m pendant la périodesurface du réservoir à un niveau bas d’exploitatiomaximum d’exploitation (cote 538 m – image de dr

flush’ operation was to export dis-solved elements from the water bodyand thus to accelerate the improve-ment of the water quality. Soils andvegetation were totally flooded by theend of October 2009 when the maxi-mum of the reservoir surface was firstreached. The water level of the reser-voir was nearly constant from October

nd of the flooded area (km²) for a reservoir water– 2013). The pictures represent the surface of the

d at the full supply level (538 m asl – right picture).

et de la surface noyée (km²) pour un niveau d’eaude suivi (2008 – 2013). Les images représentent lan (cote 530 m – image de gauche) et au niveauoite).


2009 to March 2010 and remainedunaffected by the turbine test runs dur-ing this period.

The NT2 hydropower plant startedelectricity production in March 2010and began its commercial operation inApril 2010. Since this date, the waterlevel of the reservoir follows an annualcycle under normal operation (Figs. 6and 7), with a mean annual water levelfluctuation of 8.6 m (min 7.6 m in 2010and max 9.5 m in 2011), still far fromthe maximum water level range of12.5 m at the minimum operating level.The year 2010 was an average hydro-logical year, whereas 2011 was a verywet year with a spill of 6337 m3 s-1 onthe 1st of October to the Nam TheunRiver. 2012 was a dry year with nospilling and a filling level of 1 m belowfull supply. The Power House dis-charges show a similar annual patternover years with a maximum of tur-binated waters during the dry seasonand a minimum during the wet season.Water discharge ranged from 0 to333 m3 s-1 and the annual average tur-bine discharge is 220 m3 s-1 (Fig. 6).

Since April 2008, the water releaseinto the Nam Theun River is 2 m3 s-1,corresponding to the minimum requiredriparian release (environmental flow).Short periods of higher dischargeswere recorded each year during floodevents, except in 2012 where no spilloccurred (Fig. 6).

The Downstream Channel feedsinto the Xe Bangfai River at Mahaxaivillage (Figs. 1 and 6). Xe Bangfai highflows occur in the wet season betweenJuly and November and peaked at3260 m3 s-1 in August 2011. InMahaxai, the annual average of the XeBangfai River natural flow is around

238 m3 s-1, whereas the annual aver-age of turbinated waters release isaround 220 m3 s-1. As a consequence,the doubling of the Xe Bangfai annualflow maintains a constant high flow inthe river, even during the dry season.This change in hydrology creates aback water effect 15.5 km upstream ofthe confluence with the DownstreamChannel.

The Nam Kathang River inputs andoutputs from the Regulating Pond(Fig. 6) show a similar pattern, wheredischarges generally ranged from 0.2to less than 100 m3 s-1, but a floodevent in 2011 resulted in a discharge ofup to 1278 m3 s-1 (not shown in Fig. 6).The Project has no effect on the NamKathang River discharge as the con-cession agreement defines that out-flows from the Regulating Pond to theNam Kathang must match the inflowsfrom the two tributaries, the NamKathang Ngai and Noy (except duringextreme floods, where the Down-stream Channel can be used to evacu-ate natural inflow).

4 ENVIRONMENTAL PROGRAMME

The NT2 Aquatic Environment Lab-oratory (AE Lab) was established inApril 2008, a few weeks before the firstimpoundment of NT2 Reservoir. TheAE Lab was initially setup as an NTPCindependent unit under a joint-ventureagreement between EDF and NTPC.By 2011, the AE Lab was integratedinto the NTPC Environmental Manage-ment Office (EMO). A service agree-ment between NTPC and EDF waselaborated in which NTPC (through theAE Lab) provided monitoring and


analytical services to EDF and itsresearch partners. Once installed, AELab progressively took over all tasks tofulfil NTPC’s obligations in terms ofwater quality and biological monitoringas defined in the CA.

The water quality and hydrobiologymonitoring programme was imple-mented to understand the evolution ofthe entire NT2 hydrological system, butalso to provide data to develop a pre-dictive model of reservoir water quality.This model, implemented by EDF-CIH,helps to define scenarios of the evolu-tion of the water quality over themedium term (30 years). Greenhousegases (GHG) are also taken into con-sideration in this model in order torefine the estimation of the carbon foot-print of the hydropower plant for the fullduration of concession period andanticipated lifespan.

The anticipated biomass decompo-sition under prevailing anaerobic con-ditions in the reservoir was expected toproduce GHG such as carbon dioxide(CO2), methane (CH4) and nitrousoxide (N2O). The absolute and relativeproduction and emission of these threeGHGs depend on many biological,physical and chemical parameterssuch as dissolved oxygen, tempera-ture, light penetration in the water, bio-mass production in the reservoir, etc.Therefore, the monitoring protocol fol-lowed a multidisciplinary approach witha large geographical coverage includ-ing the reservoir and its watershed, theNakai Dam and its downstream sec-tion, the Power House, the RegulatingPond and water courses downstream(Xe Bangfai tributaries and Xe BangfaiRiver). This monitoring programmeincludes (i) fundamental water quality

parameters such as nutrients andother major biological, physical andchemical elements, (ii) dissolved andtotal carbon content (total, dissolved,organic, inorganic), (iii) GHG (dis-solved and fluxes) and (iv) hydrobiol-ogy: zoo and phytoplankton, macroin-vertebrates and fish.

Research and development collab-orations were launched (particularly forGHGandblue-greenalgae)withFrenchUniversities (Toulouse and Rennes)and research institutes (CNRS, IRD andEDF SEM).

Beside monitoring and research onwater quality and GHG conducted bythe AE Lab, NTPC’s EMO developedcomprehensive environmental pro-grammes on: (i) fish biodiversity (inven-tories in both Xe Bangfai and NamTheun watersheds since 1999), (ii)wildlife rescue after reservoir impound-ment, (iii) Nakai elephant populationmonitoring and human-elephant con-flict mitigation, (iv) creation of artificialwetlands above full supply level andspecific work on turtles and tortoises,(v) conservation and propagation of theIndochinese Swamp Cypress (endemictree) populations.

4.1 The metamorphosisof the Aquatic EnvironmentLaboratory - 2009 to 2011

The AE Lab is based on the NT2Project site to facilitate logistical chal-lenges due to the high frequency ofanalysis and to ensure the quality ofmonitoring and analysis of physical,chemical and biological parameters ofall water bodies within the NT2 Projectarea.


The temporary premises of AE Labwere established in 2008 within anunused warehouse in Ban Oudomsouk(Nakai district), on the Nakai plateau.The permanent location of AE Lab andoffices was identified at the end of 2010and was confirmed by 2011 to be withinthe companies Residential Complex inGnommalth. The layout and interiordesign, as well as bidding and con-struction supervision was done in-house. The construction works and thedelivery of furniture were completed byNovember 2011. The 13th of Decem-ber 2011, the new AE Lab was fullyoperational. The 250 m2 facility isdesigned to accomplish, in-house, allthe steps of water chemistry and biol-ogy sample processing, data manage-ment, analysis and data interpretation(Fig. 8).

Fig. 8. Picture of the AE Lab Chemistry Unit (©NTP

Fig. 8. Photographie de l’Unité de Chimie du Labor

From 2008 to 2013, the AE Lab wascomposed of a team of 12 to 15 people(10-12 Lao, 1 Thai and 2-4 French).

4.2 Presentation of the monitoringstations

A total of 36 stations are monitoredwithin the Project area as presented inFigure 1 and Table II. 10 stations are lo-cated on the Nam Theun River and trib-utaries to follow the water quality of wa-ter inputs and outputs of the reservoir.9 stations are situated in the reservoirarea because of its spatial heterogene-ity among the upstream, downstreamand isolated zones. 3 are located down-stream of the Power House and 4 alongthe Downstream Channel. 6 and 4 sta-tions were respectively set up in the

C, 2013).

atoire AE Lab (©NTPC, 2013).


Table II. Monitoring stations (name and rationale).Tableau II. Stations de suivi (nom et description).

Name Location RationaleNam Theun and tributariesNTH1 Nam Theun, upstream Nam Noy

confluenceReference station, not impacted by thereservoir

NON1 Nam On, upstream reservoir Reference stations, almost not impactedby the reservoir. To analyse the differentincoming sources of carbon into thereservoir

NTH2 Nam Theun, upstream reservoir,downstream Nam Theun / Nam Noyconfluence

NXT1 Nam Xot, upstream reservoirNTH3 Immediate downstream of the Nakai

DamTo verify the improvement of the waterquality through the riparian release / Tocheck the possible improvement of thewater quality of the Nam Theun betweenNakai Dam and Theun HinbounHeadpond. Control spilling

NTH4 Nam Theun downstream Nakai Dambut upstream Nam Phao confluence

NTH5 Nam Theun downstream Nam Phaoconfluence

NTH6 Nam Theun 10 km upstream NamTheun bridge

NTH7 Nam Theun at Nam Theun bridgeNPH1 Nam Phao upstream Nam Theun

confluenceReservoirRES1 Immediately upstream Nakai Dam Downstream sector, in the area of flooded

primary forest, to measure the impact oforganic matter decomposition on waterquality

RES2 Between dam site and Ban Thalang

RES3 Nam Malou Area An area with low flow, the water quality islikely to deteriorate more severely than inother areas, with a particularly high risk offish mortality

RES4 At Ban Thalang (under the bridge) Middle of the reservoir. Narrow waterway.Transition between east and west part ofreservoir

RES5 Middle of the upstream zone Middle of the reservoir in an open areaRES6 Junction between old alignment of

the Nam Theun and the HeadraceChannel

To study the upper part of the reservoirand also check the water quality beforeentering the Headrace Channel and intake

RES7 Middle of the reservoir, in front of thewater Intake

Central part of the reservoir in an openarea

RES8 Upstream zone of the reservoir Upstream part of the reservoir in an openarea

RES9 Water intake To assess the quality of the water leavingthe reservoir


Table II. Continued.Tableau II. Suite.

Name Location RationaleCivil works and Downstream ChannelPWH Turbine in the Power Station To assess the quality of the water leaving

the reservoirTRC1 Tailrace To assess the quality of the water leaving

the Power Station, just after the turbinesREG1 Regulating Pond, close to the

LogboomsTo assess the quality of the water leavingthe Regulating Pond

DCH1 Downstream the Regulating Dam To assess the aeration efficiency of theRegulating Dam

DCH2 Upstream the Aeration Weir To assess the efficiency of the AerationWeir

DCH3 Downstream the Aeration WeirDCH4 Upstream the confluence between

Downstream Channel and XeBangfai

To assess the quality of the water leavingthe Downstream Channel

Nam Kathang & Nam GnomNKT1 Nam Kathang Noy upstream Tailrace To assess the water quality before the

impact of the Tailrace and the RegulatingPond

NKT2 Nam Kathang Gnai upstreamRegulating Pond

To assess the water quality before theimpact of Regulating Pond

NKT3 Nam Kathang downstream theRegulating Pond

To assess the impact of the RegulatingPond on water quality

NKT4 Nam Kathang in Ban That To assess the water quality a few kmdownstream of the Regulating Pond andbefore the impact of Gnommalath

NKT5 Nam Gnom upstream bridgeNational Rd 12

To assess the water quality downstreamthe confluence with the Nam Kathang

NGM1 Nam Gnom Upstream of theDownstream Channel Siphon

To assess the water quality before theconfluence with the Nam Kathang

Xe Bangfai RiverXBF1 Upstream confluence Nam Kathang Reference station, not impacted by the

development of NT2XBF2 Mahaxai, downstream confluence

with Nam Gnom and theDownstream Channel

To assess the effect of the release ofwater from the Downstream Channel inthe Xe Bangfai

XBF3 Sector located downstream from theconfluence with the Nam Gnom.

XBF4 Road 13 Bridge To assess the water quality of the lowerXe Bangfai upstream of the confluencewith the Mekong River


Nam Kathang/Nam Gnom and XeBangfai watershed to monitor the po-tential effects of the Project on theserivers.

4.3 Physico-chemical parametersand biological populations

Of the 10 groups of parametersmeasured within the monitoring pro-gramme framework, 7 are physico-chemical parameters (Tab. III). Thedesign of the monitoring programmeincluded all major elements such ascarbon, nitrogen, dissolved gases and

Table III. Bio-physico-chemical parameters monitorTableau III. Paramètres bio-physico-chimique suivi

Number Groups

1 In situ Temperature, pH, dtransparency

2 Carbonbudget

Dissolved CH4, disscarbon, total inorgaalkalinity)

3 Other majorparameters

BOD, COD, TSS, tosilica

4 HPLC Potassium, sodium,sulfate, chloride, nit

5 N2O Dissolved N2O

6 Gas fluxes Bubbling CH4, CO2

7 Chlorophyll a Chlorophyll a

8 Phyto andzooplankton

Number of individuaobservation (bloom,

9 Benthicinvertebrates

Number and identifispecies whenever p

10 Fish Number, identificatispecimens per net.analysis

some metals such as mercury. Bio-logical parameters are divided into3 groups: phyto and zooplankton, ben-thic macroinvertebrates and fish. Bio-logical compartments are monitored toassess the biodiversity and the stabilityof the habitats within the NT2 Projectarea. The monitoring of fish and mac-roinvertebrates began at the onset ofthe monitoring programme (2006),whereas phyto and zooplankton mon-itoring began by March 2009.

All sampling procedures and analy-sis follow standard protocols (ISO) orreferenced scientific methods (NTPC,2012).

ed.s.

Parameters

issolved oxygen, turbidity, conductivity,

olved CO2, total organic carbon, totalnic carbon (calculation / measurements /

tal N, total P, Fe II, Fe III, total dissolved iron,

calcium, magnesium, ammonia, phosphate,rite, nitrate, fluoride

, N2O, diffusive CH4, CO2, N2O

ls and species identification, biomass, visualhydrophytes, macrophytes…)

cation of individuals per family (per genus orossible)

on (species), size, weight, sex, maturity ofStomach content, flesh samples for mercury


4.4 Measurement frequencies

The measurement frequencies ofeach group defined in Table III are pre-sented in Table IV. Unless otherwisestated in the table, all sampling stationsdefined in Table II are measured. In-situ measurements and samplings areperformed on a weekly, monthly orseasonal basis according to the tar-geted parameters. A key focus on theunderstanding of processes occurringin reservoir and on the monitoring ofwater releases from the Power House,led to conduct sampling campaigns ona weekly and fortnightly basis. Thechemical and GHG monitoring beganwith a frequency of 75 samples pointsper month in January 2009 and stabi-lized at 150 samples per month at theend of the 2009. It resulted in approxi-mately 10000 data values per monththat are entered into a database (ana-lytical results and metadata).

Biological monitoring follows amonthly, bi-annual or a quarterly fre-quency in line with the main seasonsprevailing in the region. Phytoplanktonand zooplankton are monitored on amonthly basis in association with chlo-rophyll a determination. Aquatic inver-tebrates and fish are respectively mon-itored on a bi-annual and a quarterlybasis.

5 CONCLUSION

This is the first long term environ-mental monitoring programme in asub-tropical region (from 2008 to 2017)focusing on complex issues related to ahydropower project, such as water

quality, greenhouse gas emissions andaquatic ecology. A similar monitoringprogramme in the reservoir of the PetitSaut Project in French Guiana, pro-vided valuable lessons on the designand the implementation of the compre-hensive environmental monitoring pro-gramme for the NT2 Project, makingthe startup of the monitoring more effi-cient and effective.

This monitoring programme contrib-utes to a profound understanding ofconsequences of the reservoir im-poundment on the aquatic ecosystemand will lead to a number of uniquestudies and publications of scientificinterest.

ACKNOWLEDGEMENTS

This research has been conductedat the Aquatic Environment Laboratoryof Nam Theun 2 Power Company in LaoPDR whose Shareholders are Électric-ité de France, Lao Holding State Enter-prise and Electricity Generating PublicCompany Limited of Thailand.

The authors would like to thank eve-ryone who contributed to the NT2 mon-itoring programme, especially the NamTheun 2 Power Company (NTPC) andElectricité de France (EDF) for provid-ing financial and scientific support. Weare also grateful to the managementand staff of the Aquatic EnvironmentLaboratory and the Water Quality andBiodiversity Department, the TechnicalDivision and the Operation and Mainte-nance Division for the successfulestablishment and operation of theAquatic and Environment Laboratory.We also would like to thank Ms Léah


Table IV. Frequencies and locations of measurements per type of analysis (Tab. III).Tableau IV. Fréquences et stations de mesures par type d’analyse (Tab. III).

Group of stations Frequencies

Weekly Fortnightly Monthly Biannual

Nam

Th

eun

Riv

eran

dtr

ibu

tari

es

NTH3 - 1, 2 1, 2, 3, 4, 5 -NTH4 - 1, 2 1, 2, 3, 4, 5 -NTH5 - 1, 2 1, 2, 3, 4, 5 -NTH6 - - - 9, 10NTH7 - 1, 2 1, 2, 3, 4, 5 -NPH1 - 1, 2 1, 2, 3, 4, 5 -NTX1 - 1, 2 1, 2, 3, 4, 5 -NTH2 - 1, 2 1, 2, 3, 4, 5 -NON1 - 1, 2 1, 2, 3, 4, 5 -NTH1 - - - 9, 10

Res

ervo

ir*

RES1 (6) - 1, 2 1, 2, 3, 4, 5, 7, 8 -RES2 (3) - 1, 2 1, 2, 3, 4, 5 -RES3 (6) - 1, 2 1, 2, 3, 4, 5, 6, 7, 8 -RES4 (6) - 1, 2 1, 2, 3, 4, 5, 7, 8 9, 10RES5 (6) - 1, 2 1, 2, 3, 4, 5 -RES6 (3) - 1, 2 1, 2, 3, 4, 5, 6, 7, 8 -RES7 (6) - 1, 2 1, 2, 3, 4, 5 -RES8 (3) - 1, 2 1, 2, 3, 4, 5, 6, 7, 8 -RES9 (6) - 1, 2 1, 2, 3, 4, 5 -

Civ

ilw

ork

s

PWH 1, 2, 3, 4, 5 - - -TRC1 1, 2, 3, 4, 5 - - -REG1 1, 2, 3, 4, 5 6 - -DCH1 1, 2, 3, 4, 5 - - -DCH2 1, 2, 3, 4, 5 - - -DCH3 1, 2, 3, 4, 5 - - -DCH4 1, 2, 3, 4, 5 - - -

Nam

Kat

han

g&

Nam

Gn

om

NKT1 - 1, 2 1, 2, 3, 4, 5 -NKT2 - 1, 2 1, 2, 3, 4, 5 -NKT3 - 1, 2 1, 2, 3, 4, 5 -NKT4 - 1, 2 1, 2, 3, 4, 5 -NKT5 - 1, 2 1, 2, 3, 4, 5 9, 10NGM1 - 1, 2 1, 2, 3, 4, 5 10

Xe

Ban

gfa

i XBF1 - 1, 2, 3, 4, 5 - 9, 10XBF2 - 1, 2, 3, 4, 5 - 9, 10XBF3 - 1, 2, 3, 4, 5 - -XBF4 - 1, 2, 3, 4, 5 - -

* The number in brackets indicates the number of depths sampled per profile. Thesampling was organised to have at least one measurement per week (group 1) on thereservoir to avoid missing any particular event.


Bêche who reviewed and improved thisversion of the manuscript as a nativeEnglish speaker.

REFERENCES

Chanudet V., Fabre V. & Van Der Kaaij T.,2012. Application of a three-dimen-tional model to the Nam Theun 2 Res-ervoir (Lao PDR). J. Great Lakes Res.38 : 260-269.

Descloux S., Chanudet V., Poilvé H. &Grégoire A., 2011. Co-assessment ofbiomass and soil organic carbon stocksin a future reservoir area located inSoutheast Asia. Environ. Monit. Assess.173 : 723-741.

DTG, 2012. Rapport : Nakai Reservoir onthe Nam Theun River, capacity curvecalculation, 2012 data, Grenoble, 9 p.

DTG, 2013. Rapport : Détermination durisque de crue extrêmes de la NamTheun à Dam site (4013 km²) par laméthode SCHADEX, Grenoble, 62 p.

NTPC, 2004. Summary environmentaland social impact assessment – Namtheun 2 hydroelectric Project in LaoPeople’s Democratic Republic. Vienti-ane, 80 p.

NTPC, 2005. Environmental assessmentand management plan – Nam theun 2hydroelectric Project. Vientiane, 212 p.

NTPC, 2012. 2010-2011 Annual report.Vientiane, 254 p.

NTPC, 2013. OMD Database 1995-2013(unpublished).

SMEC, 2003. SMEC hydrology summaryreport. Memo to NTPC (unpublished).

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Main features of the Nam Theun 2 hydroelectric project ... · Main features of the Nam Theun 2 hydroelectric project (Lao PDR) and the associated environmental monitoring programmes