1. • A 335m high clay core embankment dam.
• Reservoir with a volume of 13.3km³.
• Spillway comprising an intake shaft, a tunnel and an open chute.
• Underground power house with 6x600MW installed capacity.
• Outdoor switchyard and a 500kV transmission line system.
From 1965 to 1978, the first feasibility study and a design for con-
struction of the Rogun project were developed by the Soviet design insti-
tute Hydroproject Tashkent. Preparatory construction works began in
1976 and the main construction activities started in 1982. In 1990, con-
struction activities slowed down as a result of the collapse of the Soviet
Union. The scope of work implemented from 1976 to 1990 constitutes
a significant volume of construction, comprising both underground
works and surface facilities. During a flood in 1993, the diversion tun-
nels were blocked, which caused overtopping of the 45m high upstream
embankment cofferdam which was subsequently washed away.
In October 2004, Russian Aluminium (RUSAL) and the
Government of Tajikistan reached an agreement to resume work
with the aim of completing construction of the first stage of the pro-
ject, primarily for the supply of power for existing and new alu-
minium smelters in Tajikistan.
In February 2005 RUSAL commissioned Lahmeyer International
of Germany to carry out a bankable feasibility study for Stage 1 com-
pletion of the scheme. The final report of this study was issued in
December 2006. Work included a technical review of the project
layout concepts and the elaboration of an optimal project layout. It
was necessary to determine the extent to which existing construction
works could be used in the completion project and to evaluate the
residual value of these works. Lahmeyer’s initial task was limited to
investigating the feasibility of Stage 1 of the project, with a required
generation of 5.6TWh/yr, which corresponds to a dam height of
235m. Parameters for the staged extension were to be defined by the
investor RUSAL and the Government of Tajikistan. Later, Lahmeyer
was also commissioned to prepare a study on the optimal project para-
meters, to assess the final dam height and the related optimal installed
capacity. This study identified the optimal height of the Rogun dam
T
HE Republic of Tajikistan owns almost 4% of the world’s
hydro power resources, ranking eighth in the world on an
overall basis, and first on a per-capita basis. More than 95%
of electricity in Tajikistan is generated by hydro plants.
Rogun hydroelectric project is located on the Vakhsh river, and is the
uppermost project in a cascade of plants which also comprises:
• Nurek (3000MW).
• Baipaza (600MW).
• Sangtuda 1 (670MW, under construction)
• Sangtuda 2 (220MW, in planning)
• Golovnaya (240MW).
• Perepadnaya (30MW).
• Centralnaya (15MW).
The Vakhsh river basin is located within the Pamir-Altai Mountains
and, with a drainage area of some 39,000km², it is fed from snow-
fields and glaciers. Because of its mountainous terrain, the Vakhsh
is heavily loaded with sediments, especially in the upper stretch
where Rogun is located. The annual runoff of the Vakhsh river at
the Rogun site is approximately 20km³, corresponding to a long
term average discharge of 635m³/sec and a mean annual power gen-
eration of up to 14.5TWh/yr (at a 335m dam height). At the dam
site, the Vakhsh river flows through a narrow, 400-500m deep, V-
shaped gorge, with slopes of both banks as steep as 50°. Rogun HEP
will not only generate power but will also have positive effects on
the existing downstream hydro power plants, particularly increas-
ing the energy output during winter.
PROJECT HISTORY
The Rogun project was conceived as a dual-purpose project for irri-
gation water management at Amu-Darya river and for hydroelec-
tricity. The original project’s main components were:
30 MAY 2008 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PLANNING AND PROJECTS
Construction of the Rogun hydroelectric project was suspended after the break-up of the
former Soviet Union, but work at the site in Tajikistan is expected to be resumed in the
near future. Roland Schmidt reports on the challenge of completing this complex project
Table 1: Key parameters of the
staged development of the
Rogun project
Parameter Stage 1 Stage 2 Stage 3
Dam height (m) 225 285 335
Full supply level (el. m) 1180 1240 1290
Minimum operating level (el. m) 1120 1180 1230
Initial reservoir volume (km³) 2.78 6.76 13.3
Initial life storage volume (km³) 1.92 3.98 10.3
Total installed capacity (MW) 1200 2400 3600
Number of turbine units installed 3 4 6
Average generation (TWh/yr) 6.7 11.6 14.5
Additional generation by the d/s
cascade (TWh/yr) 0.4 0.9 1.2
Onwards and upwards
The largely completed underground works for the Rogun scheme

2. WWW.WATERPOWERMAGAZINE.COM MAY 2008 31
to be at or slightly above 285m, corresponding to Stage 2, with the
installed capacity and related parameters shown in Table 1.
SCOPE OF EXISTING WORKS
The existing Rogun scheme consists of multiple incomplete facilities
erected during the construction period from 1976-90, part of which
can be used for the new project after rehabilitation. The existing civil
works comprise underground works, temporary and permanent
roads, site utility systems (power and water supply, sewage), existing
construction materials (e.g. more than 14Mm³ of stockpiled aggre-
gates) and reservoir preparation works. On one side, the existing
works, namely access roads and tunnels, provide immediate access
to the construction site itself and thus will allow earlier diversion of
the Vakhsh river than in the hypothetical case of the same site in
virgin condition. On the other side, the existing works have deterio-
rated and are partly obsolete, requiring securing or demolishing.
Most of the unused tunnels are to be backfilled and sealed off with
concrete plugs. Such measures will incur additional costs but these
can be offset by savings from the reduced construction time.
Hydraulic steel structures already onsite could partly be used in
the completion project. In view of the outdated design and make of
the existing electromechanical equipment, it is recommended that
these parts be replaced with modern equipment.
SITE GEOLOGY
Besides the extraordinary dam height, other challenges exist at the Rogun
project. The heterogeneous bedrock at the dam site is composed of
Jurassic and Cretaceous sedimentary systems, with some intercalations
of gypsum. A wedge of salt fed by the Gaurdak salt formation is squeez-
ing upward along the Ionakhsh fault, which crosses the reservoir and
will therefore become submerged. Where this fault approaches the sur-
face, the salt is leached, leaving a 10-12m wide zone of soft residue. With
depth, the thickness of salt increases progressively. Hydrogeological and
geotechnical modelling had indicated a risk of accelerated leaching of
the Ionakhsh salt wedge with the raising of the reservoir level and, as a
result, undesirable settlements at ground level. Therefore, at the river
diversion stage of the original project, a system of protective measures
were put in place, including local salt replacement, grout curtains acting
as hydraulic barriers and injection wells to compensate hydrogeological
and hydro-chemical gradients. Extensive grouting barriers are yet to be
implemented at the construction completion project.
HIGH SEISMICITY
The territory of Tajikistan extends from the border of the Eurasian
Plate with the Tienshan range in the north to the border of the
Indopacific Plate with the Pamir in the southeast. Convergence of
the two plates causes compression in the intercalated tectonic unit
of the Tajik Depression. The compression results in an imbricate
structure of thrust sheets in the sediments of the Tajik Depression.
From a seismo-tectonic point of view, the deep crustal Hissar-
Kokshaal fault ranks foremost for the project. This is a reverse fault
of the first order, which extends for several hundred kilometres and
has accumulated a displacement of several kilometres. Another
regional fault, the second order Illiak-Vakhsh fault, follows 1-2km
to the south of the Hissar-Kokshaal fault. These thrust faults are
rooted in a decollement surface, developed at 5-10km depth in the
Jurassic salt formation.
The Rogun dam site is framed by two regional third order faults:
Ionakhsh upstream and Gulizindan downstream of the site. Both are
reverse faults of some 100km in length with a cumulated displace-
ment in the order of 1km. Annual displacements in the order of 1-
2mm were determined in the course of the project investigations. As
could be established in the course of the very comprehensive micro-
seismic monitoring during the filling of the nearby Nurek reservoir,
the displacement on the Ionakhsh fault mainly occurs as aseismic
creep. As a result of the lubricating effect of the Gaurdak salt, brittle
events of small magnitude on minor faults in the adjacent strong sed-
iments accompany this creep. Consequently, fairly large displacements
can be predicted on the faults at the dam site, including possible sym-
pathetic movements in the decimetre range on the higher order shears
and faults in the rock mass forming the dam foundation.
Earthquakes occur in Tajikistan almost on a daily basis, mostly
with magnitudes below 5.5 on the Richter scale. The strongest earth-
quakes recorded in the wider region were the Karatag earthquake
of 1907 with M=7.3, and the Khait earthquake in 1949 with M=7.6.
A peak ground acceleration in the horizontal direction of 0.56g was
applied for the feasibility design of the dam type options studied. In
view of the experience gained regarding reservoir induced seismici-
ty at Nurek, the possibility of a triggered earthquake up to M=6.6
has been acknowledged.
RECOMMENDED PROJECT COMPLETION
The recommended project layout for completion comprises a rock-
fill embankment dam, in combination with an underground power
house, on the left bank of the river, using the largely excavated
cavern. The proposed layout of the dam, power house and river
diversion is similar to the original design of 1978, whereas the design
and layout of the spillways, mid-level outlet and tailrace tunnels were
essentially modified by Lahmeyer. Another major modification intro-
duced is the 175m high start-up dam, which is integrated in the main
dam and allows commencement of power generation some 3.5 years
prior to stage 1 completion.
Four different dam type options (rockfill embankment dam,
CFRD, arch gravity and concrete arch dam), in combination with
two powerhouse variants (surface and underground), were studied
by Lahmeyer. Taking into account the heterogeneous bedrock with
PLANNING AND PROJECTS
Sector gates for flow control through diversion tunnels. Three gates were to be
installed in each tunnel
Recommended layout of the permanent structures for Rogun hydroelectric
project (Stage 1)

3. horizons of low shear strength, and in view of the present active
faults, a conservatively designed embankment dam with clay core
was identified as the preferred option, as this involves the least
amount of uncertainties in design and construction. Embankment
dams have a high resilience to foundation deformations and are there-
fore better suited than a brittle concrete dam or a CFRD.
Furthermore, the Nurek dam located 70km downstream, with its
world record height of 300m, constitutes a valid precedent for the
selected dam type option. The Stage 1 dam is 235m high and requires
a rockfill volume of 33.6Mm³. The main axis and the central clay
core of the embankment dam remains at the originally planned loca-
tion; thereby, maximum use is made of the already existing excava-
tion for the core trench. The height of the dam can be increased up
to el.1250 (or even higher) during Stage 2 of construction.
The optimal parameter study showed that the optimal installed
capacity for Rogun is 2400MW. Three Francis turbines will there-
fore be installed in Stage 1, which are rated 600MW for the final
stage. Provisions will be made for a fourth unit to be installed in Stage
2. During Stage 1, partial load operation will yield approximately
400MW per unit. In view of the large dimensions (inlet diameter
5.7m) at some 30 bar, gate valves will be applied as control valves,
which will be integrated in the turbines. The main transformers will
be located in a separate cavern 18.5m wide, which will also house
the gas insulated switchgear (GIS). Power evacuation is by GIS and
500kV cables, through one out of the two existing cable galleries.
For each power generating unit, a separate power intake, head-
race tunnel, pressure shaft and pressure tunnel is provided on the
left bank. The three power intakes for Stage 1 are located at invert
el. 1100, each equipped with trashracks and recesses for bulkhead
gates. Different to the original design of 1978, new tailrace tunnels
will be built, independent from the diversion tunnels, with power
outlets integrated in the downstream RCC toe dam. In case of imple-
menting the project with an integrated start-up dam, two turbine
units with temporary power waterways will be commissioned on
completion of the start-up dam, for early power generation.
RIVER DIVERSION
Both partly existing diversion tunnels DT1 and DT2 on the left and
right banks will be rehabilitated and used to divert the river during
construction. The use of these tunnels, designed to cross the down-
stream dam embankment through a concrete culvert structure,
requires extensive repair of large rockfalls. These had occurred at
the intersections of temporary lined tunnels with the existing faults,
particularly Fault 35.
The tunnels are each about 1480m long. In the 320m long part
upstream of the gate section the tunnels run under pressure, except
during very low flows, and have a D-shape cross-section (11x11m).
Downstream of the control gates, each tunnel constitutes, hydrauli-
cally, an open channel, with a D-shape section of 14x17m. The
intake invert of DT1 is about 10m lower than DT2, to facilitate river
damming and diversion. By modifying the invert slope, maximum
flow velocities downstream of the control gates kept below 24m/sec,
for a 1 in 50-year flood.
One upstream and two downstream rockfill cofferdams are to be
constructed, for diversion of river flow during construction. To
divert the river through the left bank reach of diversion tunnel DT1
and the auxiliary tunnel, initially a rockfill diversion bund will be
constructed up to el.1000. This will subsequently be extended up to
el. 1044, which is sufficient to generate the head required for divert-
ing the 50-year design flood of 3550m³/sec. Thus, a 70m high cof-
ferdam will need to be constructed in one season, and will become
an integral part of the main dam. In parallel, the rockfill cofferdam
CD2 is built up to elevation 984m asl for protection of the dam site,
PLANNING AND PROJECTS
32 MAY 2008 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
Staged construction of the Rogun embankment dam. After diversion of Vakhsh River, via the diversion bund (olive), the 70m high integrated cofferdam (orange)
is constructed and extended to el. 1110 as an integrated start-up dam (navy blue), which is then heightened to el. 1140 (red). Subsequently, the Stage 1 dam
height is reached in horizontal layers (different blue tones). Heightening to Stage 2 requires comparatively small fill volumes (beige).
Layout of the river diversion works
Environmental and social impacts
The Stage 1 reservoir at Rogun would inundate about 1600ha of cultivated
land, of which one-third is arable and the remainder is pasture. Biodiversity is
comparatively low, and there are no important habitats or rare species which
would be endangered. The population of the valley upstream of Rogun
consists almost entirely of ethnic Tajiks who are generally farmers and
herdsmen. A preliminary cost estimate of the environmental, social and
reservoir preparation measures directly associated with Stage 1 of the
project resulted in a figure of about US$250M, inclusive of the residual value
of measures already implemented. The largest items are replacement of
flooded transport, power and telephone infrastructure. The most complex
issues are resettlement planning and implementation.

4. WWW.WATERPOWERMAGAZINE.COM MAY 2008 33
PLANNING AND PROJECTS
which will allow for construction of the culvert section for river
crossing of diversion tunnel DT2. In the subsequent dry season, the
river will be diverted through DT2, which allows construction of
the culvert section for DT1. In parallel, the auxiliary tunnel is closed
and downstream cofferdam CD3 is constructed to seal the down-
stream dam foundation against the Vakhsh river.
SPILLWAY CONCEPT
The ability to pass large floods is crucial for the stability of the Rogun
embankment dam, meaning a carefully elaborated and conservative
design is applied for the spillway. In the 1978 design the spillway had
a limited discharge capacity of 3400m³/sec, corresponding to almost
60% of the 10,000 year flood. Such a flood could only be passed by
considering the full retention of the Rogun reservoir and ensuring six
turbine units are in operation. From today’s standards this design
philosophy is not suitable for a rockfill dam, which would not with-
stand overtopping for a longer period; hence the spillway constitutes
the weak point in the original design.
The spillway concept proposed by Lahmeyer has therefore been
designed for the PMF of 7500m³/sec, and it consists of a combina-
tion of the following structures:
• An open chute spillway on the right abutment, for at least 50% of
the design discharge, corresponding to a specific discharge of about
83m³/sec per metre width of the 45m wide chute.
• Two tunnel spillways on the right bank, each for about 25% of
the design discharge.
The free flow sections of tunnels and chutes each include a number
of aerators to avoid damage on concrete surfaces by cavitation,
which is a critical issue with flow velocities reaching up to 50m3/sec
for Stage 2. Both Flip buckets at the exits of the chute and tunnels
are located such as to ensure the jets will enter in a huge plunge pool,
which is located downstream of the power outlets and the RCC toe
dam, providing a sufficient water cushion depth for energy dissipa-
tion from heads of almost 300m. The large scale of the related exca-
vation works requires detailed studies on work methodologies,
during the next project stages.
A temporary mid-level outlet tunnel, with intake at el. 1070 on
the left bank and aligned above the two diversion tunnels, crosses
the downstream dam embankment and discharges into the plunge
pool. The mid-level outlet will be temporarily used for controlled
impoundment and to provide additional safety by being less exposed
to bed loaded flow than the two diversion tunnels; it becomes redun-
dant and will be permanently plugged after the completion of the
final stage of the open chute spillway.
This spillway concept, which was proposed by Lahmeyer for the
safe evacuation of floods from heads as high as 265m, necessitates
a huge, partly pre-excavated plunge pool downstream of the dam.
The extent of the related excavation and sloped protection works
constitutes a major drawback of this proposal, which would be
largely avoided if vortex tunnels were applied instead of the high
level spillway tunnels with ski jump at their end.
Such a scheme, which could perhaps integrate the existing diver-
sion tunnels, had been proposed and extensively tested by a
hydraulic scale model by the Scientific Research Institute of Energy
Structures (NIIES) in Moskau. The flows enters the vortex spillway
through a vertical shaft with a crown section at its bottom, where
the cross sectional area is reduced and accordingly the maximum
velocity occurs. The eccentric connection to the adjacent tunnel sec-
tion causes axial rotation of the flow and high energy dissipation
Longitudinal section through the
tunnel spillways and plunge pool
Vortex tunnel spillway system proposed
for Stage 1 of Rogun (RUSAL 2005)

5. 34 MAY 2008 INTERNATIONAL WATER POWER & DAM CONSTRUCTION
PLANNING AND PROJECTS
due to wall friction of the vortex flow.
Up to now, only one prototype of a vortex-type spillway of com-
parable dimensions has been constructed – the spillway system of
Tehri dam in India. This comprises an open chute of some
5500m3/sec capacity, four vortex tunnel spillways and two large
open chutes. Experience gained during its operation, which started
in 2006, was not available to Lahmeyer but should be used to con-
firm or to modify the design if this concept is considered a viable
alternative for the Rogun project in the future.
Particular attention has to be paid to the risk of cavitation, which
could be caused by instabilities of the vortex flow in the tunnel.
Potential damages would be accelerated, if sediments enter into the
shaft, eg via density currents. The high velocities near the tunnel wall
cause abrasion, especially in the case of sediment transport. Further
investigations would be required concerning the admissible operat-
ing conditions, the necessity to include a control gate, and the scale
effects of the 1:50 model on the two-phase (water-air mix) flow.
If including vortex tunnels in the spillway concept it would be
mandatory to maintain the open chute, which could, during an
extreme flood, also be operated significantly above the designed dis-
charge capacity, whereas the discharge of the vortex tunnel spillways
is limited by the capacity mainly at the crown section.
ECONOMICS
To shorten the overall construction time of the project, the tendering
period for the main civil works contract should be used for starting
some preparatory works under pre-contracts. Some of these works
are currently already underway, eg rehabilitation of access roads and
selected administrative and residential buildings in Rogun City.
The filling works for the integrated start-up dam can only com-
mence after the completion of the river diversion works. Then, after
the integrated start-up dam has reached approximately el 1100m,
the temporary turbine units can be commissioned. An estimate of
about 8.5 years has been given for the duration of the Stage 1 con-
struction works under the main contract for the recommended
option of a clay core rockfill dam with integrated start-up dam,
assuming monthly filling rates of up to 580,000m³ in total.
Heightening the dam to Stage 2 would require the additional back-
filling of 8Mm³, which could be completed within less than two years.
The Stage 1 investment cost for the project, including contingencies,
amount to about US$1.94B (2005 prices), of which 68% are civil works
cost, 17% electromechanical equipment cost, and 11% mitigation costs
for environmental and social impacts. The incremental investment cost
for Stage 2, with almost double energy yield than Stage 1, only amounts
to US$0.5B or about 25% of the Stage 1 investment cost.
An economic analysis was carried out for evaluation of the hydro
power options studied from the viewpoint of the national economy
in Tajikistan. This considered the project costs (without customs,
taxes and other duties) and assessed the benefits of the project by
the power and energy of Rogun, as well as the additional or reduced
power and energy of the downstream cascade, and it valued bene-
fits by the costs of the alternative (thermal) power generation.
The economic analysis clearly identified the layout option with
rockfill embankment dam as the optimum solution, despite neces-
sitating the highest investment costs and 10 months longer for con-
struction compared with the option of a CFRD.
The dynamic unit cost (ratio of the cumulated benefit and cost
streams, discounted over the disbursement and repayment periods) are
US¢3.9/kWh at a discount rate of 8.5%; the dynamic unit cost reduces
to US¢2.5/kWh in case of a combined development of Stage 1 and 2.
Similarly, the project benefits increase, as shown by the economic inter-
nal rate of return (EIRR), which improves from 11% for the Stage 1
project to 16% for a combined development of both stages.
Evidently, the incremental capacity and energy (between Stage 1 and
Stage 2) is highly attractive economically. For some US$430 per installed
kW it would be feasible to double the energy output. These results clear-
ly support the development of Rogun in a single stage to the optimum
height of about 285m, provided that the demand for electricity in the
local and regional power markets materialises in the near future.
KEY ISSUES FOR COMPLETION
The first priority for project completion is a final decision on the
ultimate height of the Rogun dam, which needs to be agreed among
the Government of Tajikistan, riparian states involved in the pro-
ject, and the investor and/or international financial institutes who
may become involved in the scheme.
According to definitions by international financing institutions, the
Vakhsh river, as a tributary of Amu-Darya, is a transboundary river,
and as such, is beyond exclusive control by a single party. In line with
regional and international inter-state agreements on the use of water
resources, Tajikistan should notify and consult with the downstream
states before modifying the Vakhsh river’s hydrology. The successful
initiation of such a notification process is a prerequisite for safe-
guarding financing of the project and its implementation.
Normally, the optimal dam height (which corresponds to about
285m for Rogun), is chosen as the final dam height. In view of the
favourable EIRR of the project, which declines only slowly when
increasing the height above the optimum, and considering that the
Rogun scheme and its size constitute a unique project opportunity,
it is understandable that the Tajik Government opts to fully utilise
the dam site potential. Also, an investor/financier may agree on a
final dam height even slightly above the optimal one, provided that
imminent transboundary impacts will be addressed and mitigated
accordingly with the downstream riparian states of Uzbekistan,
Turkmenistan and Afghanistan, which rely on the Amu-Darya river’s
summer flows for irrigation. Obtaining the consensus by these states
to the Rogun project would probably be facilitated, if the rule for
the combined operation of the Rogun and Nurek reservoirs would
essentially preserve the current discharge regime, as considered by
Lahmeyer in the optimal parameters study.
After agreement has been reached concerning the final height, the
Stage 1 feasibility study needs to be amended accordingly. Since
RUSAL has in the meantime withdrawn as financier of the project,
the Government of Tajikistan has invited international financing
institutions to provide funds to update the study.
To safeguard the financing of the project it is crucial to justify the
project economically. While RUSAL had planned to use a major por-
tion of the generated energy for expanded aluminium production
capacities, financiers such as the World Bank would opt for satisfy-
ing suppressed local demands and for energy exports.
This would require a detailed assessment of different power mode
options (base, mixed, peak), in due consideration of the existing alu-
minium industry’s electricity demand and the corresponding propor-
tion of electricity provided by Rogun to national and the most promising
external markets. Within the frame of a further detailed demand-supply
balance, the seasonal energy supply characteristics and the various
energy qualities need to be modelled and assessed.
Dr.-Ing Roland Schmidt, Department Head of
Hydropower and Hydraulic Structures Design,
Lahmeyer International, Germany.
Email: Roland.Schmidt@lahmeyer.de
References
Lahmeyer International 2006: Rogun Hydroelectric Plant in the Republic of
Tajikistan, Bankable Feasibility Study for Stage 1 Construction Completion
Lahmeyer International 2006: Rogun Hydroelectric Plant in the Republic of
Tajikistan, Justification of Optimal Parameters of Rogun HEP on Exemplary
Basis for Clay Core Earthfill Dam
Lahmeyer International 2006: Rogun Hydroelectric Plant in the Republic of
Tajikistan, Detailed Evaluation of Existing Construction & Equipment
Schmidt, R.; Zambaga-Schulz, S.; Seibitz, M. 2006: Bankable Feasibility
Study for Rogun HEP Stage 1 Construction Completion in Tajikistan. Dams
and Reservoirs, Societies and Environment in the 21st Century (ICOLD-
SPANCOLD), Vol.1, pp 405-413
Schmidt, R. 2007: Feasibility study for completion of the Rogun scheme,
Tajikistan. Hydropower & Dams, Issue 3
IWP& DC