Techno-Economic Assessment of the Proposed Rogun Hydropower Project

Coyne et Bellier TEAS Consultants

HYDROLOGY

Presented February 2013

TEAS Panel of Experts (PoE) Membership

Roger Gill (Chair) - Hydropower Policy Expert

Ljiljana Spasic-Gril - Dam Engineering/Dam Safety/ Seismic Engineering Expert

Paul Marinos - Engineering Geology/Rock Mechanics Expert

Ezio Todini - Hydrologist

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OBJECTIVES AND CONTEXT

Report RP07 presents a comprehensive review of the existing documentation and studies and the derivation of the design parameters for the TEAS of Rogun Hydropower project.

Report RP07 includes: Assessment of hydro-meteorological and climatic conditions

and data Quality and reliability of available data and their sources Extreme flood values estimation Climate change impacts and suggested adaptation

measures

The proposed Rogun Dam project

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The proposed Rogun Dam site is located on the Vakhsh River flowing from the Pamir Mountains.

The dam site is 74.6 km upstream from Nurek Dam, and would be the uppermost dam of the current Vakhsh Hydropower Cascade System.

At the proposed Rogun dam site the Vakhsh drains a catchment area of 30390 km², approximately 30% of which lies above 4000 m asl within the snow and glacier cover zone.

Assessment of hydro-meteorological and climatic conditions and data

The hydrological study is based on a review of the previous studies, the most recent of which are:

Rogun Hydroelectric Plant (HEP) in the Republic of Tajikistan, Bankable Feasibility Study for Stage 1 Construction Completion, volume 3 D on Hydrology, Lahmeyer International in co-operation with Hydroproject Institute Moscow, January 2006.

Rogun Hydroelectric Plant on the Vakhsh River in the Republic of Tajikistan, Final Design, volume II-2 Hydrometeorologic conditions, Hydroproject Institute Moscow, 2009.

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The Hydrological Regime

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The Vakhsh catchment is mainly controlled by snow melt and glacier contribution.

The region is under continental climate, which is characterised by a wide temperature range during the year. The coldest month occurs generally in January, with minimal temperature around -30°C.

In the lower part of the catchment the yearly precipitation totals vary from 800 to 950 mm. In the upper part of the catchment, the yearly amount of precipitations can be close to 2000 mm.

A particularity of the climate of central Asia, is that the maximum precipitation amount occurs during winter. Approximately 60% of the annual precipitation falls during February and March.

The majority of precipitation in the Vakhsh catchment is stored during winter time as snow cover.

Hydro-meteorological regime

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Hydro-meteorological stations

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Hydrometric data available

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Hydrometric Gauging stations in the Vakhsh River Basin

Rogun Reservoir Inflows

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Inflow record is not homogeneous. It was combined by merging the following observations:

From 1932 to 1972, discharge recorded at Tutkaul gauging station;

From 1973 to 1988, discharges at Tutkaul re-constructed from observations in Komsomolabad. Correlations between the two stations are based on period of common recording (1949-1957 and 1963-1972);

From 1988 to 2003: discharges are calculated based on Nurek HEP inflows issued by Nurek operation unit.

Extreme Floods Study

The flood study conducted for the proposed Rogun Dam site is based on two approaches:

An Extreme Values statistical analysis of Vakhsh extreme discharge data, completed by a regional analysis, using the station-year approach;

PMF assessment based upon statistical extrapolation and an original approach based on the degree-day factor.

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Regional extreme values (EV) analysis results

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EV final accepted result

Probable Maximum Flood (PMF) assessment

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Vakhsh maximum discharges are not correlated with precipitations. Consequently, as discussed in Lahmeyer Internation & Hydroproject Moscow, 2006, PMF cannot be assessed using the conventional approach proposed by the World Meteorological Organisation (2009).

Two principal phenomena are dominant in the Vakhsh basin:

The availability of snow and ice cover accumulated in the preceding winter season;

The melting process in spring and summer, which is controlled by solar radiation.

This has led to using an original and specifically designed PMF assessment approach based on the degree-day, which was used together with the Lahmeyer 2006 estimate.

Probable Maximum Flood (PMF) assessment

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PMF final accepted result

PMF(peak)=1.05 PMF(daily)

Design Hydrograph

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Climate change impacts

Extrapolation from past observations is unreliable due to the lack of significance of the resulting regression models.

The distribution of climate change given by several models for the years 2020, 2050 and 2080 was then extracted from René Roy report relevant to Tajikistan and Kyrgyz Republic, and extrapolated to 2100.

All the climate models are rather consistent at predicting an increase in temperature;

This is not so for precipitation, because the dispersion of results is of the same order of magnitude, if not larger, than the expected precipitation rate of change;

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Climate change impacts (cont.)

Assessment of potential climate change impacts indicates that the most likely scenario is a gradual decrease in flood peak volumes because of earlier and longer melt seasons linked to increased temperature and glacier retreat.

A change in discharge annual distribution could also lead to an increase in value of annual average discharge.

This confirmed that the value of PMF chosen independently to this expected trend is conservative as peaks could be expected to decrease in future.

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Climate change adaptation measures Reduction of predictive uncertainty by improving: understanding of climate variations general circulation models downscaling approaches

Reduction of vulnerability by identifying populations at risk and by incorporating mitigation measure in the planning phase;

Changes in land use and settlements localization to be implemented when reduction of vulnerability cannot be reached;

Expansion of monitoring systems and implementation of early flood forecasting systems to improve operational flood risk management and flood warning.

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