- 1 -

The Usoy Dam, Lake Sarez and Possibilities of Geophysical Methods

U. Abdullaev S. Abdullaev P. Blaha A. Akhmedov S. Khudobakhshova Institut UZGIP Gidroingeo GEOtest, a.s. Dept. of Geology Dept. of Geology Navoiy koch 44 Olimlar str. 64 Smahova 112 27 Tursunsoda str. 27 Tursunsoda str. 100021 Tashkent 7000041 Tashkent 627 00 Brno Dushanbe Dushanbe Uzbekistan Uzbekistan Czech Republic Tajikistan Tajikistan

1. Introduction Man cannot live without water and there is no life without water. Astonishing works were built as early as the prehistoric times of human civilization. Even in modern time, we admire Iranian qanats, Roman aqueducts and other hydraulic structures of ancient times and the Middle Ages. Modern techniques have enabled works totally surpassing the visions of older generations to be built. Let us mention the highest completed dam in the world at Nurek in Tajikistan, the largest hydroelectric plant Three Gorges in China and also the longest dam in the world – Hirakud in India. Yet, the highest dam in the world was not built by man, but created by nature itself. A hundred years ago, during an earthquake in Tajikistan, a rock-fall took place, burying the village of Usoy and damming the River Murgab. The volume of rocks displaced by slope movement is estimated at two cubic kilometers. Behind the newly formed dam 650 meters high, a lake has been created over years, having a volume of about 17 km3 and a length of 60 km. The width of the dam crest is about 4.5 km and the length of the downstream face reaches 3.9 km. The dam lake of an area of 80 km2 has a mean depth of 212 meters and the maximum depth reaches five hundred meters. The mean annual oscillation of the water level is 6.6 meters and the maximum-detected annual fluctuation is 12 meters. The mean inflow into the lake is 45.7 m3 and the mean outflow is 45.1 m3. Practically the entire outflow corresponds to seepage through the dam and the opening of this seepage is now at a distance of only 1,500 meters from the water surface in the dam lake. Because the dam is natural, this seepage is uncontrollable and, together with head erosion, poses the highest risk to this creation of nature. Seepage through this dam sometimes increases up to 170 m3/s, thus increasing head erosion up to 45 meters a year. Another risk at Lake Sarez is posed by slope deformations. The most serious situation is with the so-called Right-Bank landslide lying in close proximity to the “right-bank” keying of the dam. A rapid movement of the landslide that may pass into falling could trigger a wave which would overtop the dam crest and could cause its stronger erosion. The other slope deformations do not pose such a threat, especially because the vicinity of Lake Sarez is practically an uninhabited area. 2. The Results of Geophysical Work that Was Carried Out Survey work in the area of the Usoy dam and Lake Sarez is very difficult. Obstacles are climatic conditions, impassability of the terrain and its difficult accessibility. Only a single borehole was collared during the entire existence of the dam and lake. In addition to drilling, indirect survey methods – geophysical measurements – were also used. These included geoelectrical, magnetometric, thermic and gravimetric methods as well as methods of seismic survey.

Resistivity and temperature of water were measured in the dam lake itself in the area adjacent to the dam. In addition, sonar measurements were used to identify the shape of the bottom. A great majority of geophysical work was carried out during the existence of the Soviet Union, mainly at the end of the 1970s. It is very difficult to obtain the results of such measurements, particularly as far as the primary results are concerned, i.e. the field diaries and background materials providing the data on the location of geophysical measurements. The authors of this paper managed to obtained the outputs of some work, namely at the geological workplaces in Dushanbe and Tashkent. It is probable that all the data were also stored in some of the Moscow archives, but these are now unavailable to the authors of this paper. Despite all such problems, we were successful in obtaining an overview of the types of geophysical work that had been carried out at the site of interest. We want to share the results obtained in this period of work with all colleagues and show what knowledge has been gained using geophysical measurements, what can be acquired by possible reinterpretation

- 2 -

and what other possibilities of geophysical work exist in the investigation of the site concerned, particularly with the use of new methods of measurements and their processing. In the past, geophysical work was chiefly focused on the body of the dam that had formed by slope movement on the right slope of the River Murgab. The purpose of these studies was to identify the structure of the natural dam and to contribute to the knowledge of the seepage pathway that enables a discharge of about 45 m3/s. The other group of work can also include measurements of resistivity and temperature of water just behind the dam. Also, geophysically, slope deformations were studied on the banks of Lake Sarez. The location of the site is depicted in Figure 1. In addition to the dam lake, the position of individual landslides and main watercourses, the upper part of the photograph also shows a satellite view of Lake Sarez (©GoogleEarth 2011). The map of the area of interest also indicates the measurements that were carried out at the individual sites. The background information that we have managed to obtain shows that the following types of work were applied at the individual sites: • The Usoy landslide (the body of the dam)

o Gravimetric measurement o Magnetometric measurement o Vertical electrical sounding o Low-frequency sounding o The charged body o Seismic refraction o Non-longitudinal seismic refraction o Measurement of water resistivity on the lake o Measurement of water temperature in the lake o Monitoring (leveling, geodetic monitoring)

• The Right-Bank landslide (“Pravoberezhniy sesuv”) o Seismic refraction o Non-longitudinal seismic refraction o Monitoring (extensometry, leveling, geodetic monitoring)

• The Left-Bank landslide (“Levoberezhniy sesuv”) o Seismic refraction o Non-longitudinal seismic refraction o Geoelectrical measurements o Magnetometric measurements o Monitoring (leveling, geodetic monitoring)

• The Bazaytash landslide o Non-longitudinal seismic refraction o Monitoring (geodetic monitoring)

• The Batasayf landslide o Non-longitudinal seismic refraction

• The Severniy Kazankul landslide o Non-longitudinal seismic refraction

• In addition, gravimetry was used at two sites on the left bank of the lake (Fig. 1). Profile measurements made on the dam of the lake are shown in Figure 2. Only some results obtained from the individual methods were selected for the figure. The left upper part of the figure shows a map of the Usoy landslide with depicted profiles according to the type of measurements made. We can see that the whole area of the landslide (dam) was covered with magnetometric measurement; in addition, the area of the dam crest also with gravimetric measurement. In the places in which the seepage of water was expected from the lake into the River Murgab, more magnetometric and gravimetric profiles were added and the measurement was supplemented with the methods of vertical electrical sounding, low-frequency sounding and the charged body. In addition to these measurements, seismic profiles (one of which drawn through the entire dam) and one long profile using low-frequency electrical sounding were made on the dam. An illustration of the results of vertical electrical sounding is given in the upper right part of the figure. The field measurement was obviously carried out with a smaller depth range, hence it was impossible to judge the thickness of the slipped material. However, we consider important the possibility to determine the places in which an increased flow of groundwater through the dam can be expected (the blue areas in Fig. 2). The clayey or fine sandy fraction was washed out by water flowing from the lake, or from a tectonic fracture in the left slope of the valley. As a result, the resistivity values of this layer increased to 220 – 450 Ωm. It is therefore possible to express an assumption that the vertical electrical sounding would enable the preferred pathway of groundwater to be determined, both from the lake and also from the right side of the mountain range.

- 3 -

The middle part of Figure 2 shows the results of profile measurements on profiles P6 and 2S. The magnetometric measurements show that the detected anomalies are local and cannot be correlated to a greater distance. The anomaly of the vertical component of the Earth’s magnetic field (Z), having a magnitude of about 300 nT and detected on profile P6, could not be correlated to other profiles. The anomaly is thus obviously caused by a sporadic block of magnetic rocks, which was snatched and dragged down with other non-magnetic rocks during slope movement. Residual anomalies of ∆g were detected on gravimetric measurements, having magnitudes up to 3 milligals (mGal). The interpretation of gravimetric measurements will be described below. The resistivity of the surface layer was plotted into a graph from the measurement of low-frequency electrical sounding on profile P6. This varies from 10 to 380 Ωm. This, together with the rapid changes in its thickness (10 to 180 meters), indicates a large variability of the materials of the dam. The lowest graph in Figure 2 shows the results of seismic measurements, both longitudinal and non-longitudinal. The results of measurements show

Engineering-geological mapping (scale 1:100000)

Engineering-geological mapping (scale 1:25000)

Engineering-geological mapping (scale 1:5000)

Seismic refraction

Nonprofiling seismic refraction

Geoelectrical measurement

Gravimetric measurements Geodetic measurements

Magnetometric measurements Leveling

Extensometry

S

S

S

E

E

e

e

g

g

g

gg

gg

gEM

N

N

N

N

N

N

N

M

M

G

G

S

Usoy Landslide

Shabay River

Limgar R. Katta M

ardjaraya R.

Batasaif R.

?

?

Daguk R.

Kadara R.

Birom Bonf R.

Sat Kon R.

Bist R.

Berguobin R.

Murgab R. Pravoberezhniy L.

Levoberezhniy L.

Bazaytash L.

Batasayf L.

Severniy Kazankul L.Zeneniy L.

Zeneniy R.

Lake Sarez

l

l

ll

) 0 5 10 km

Fig. 1 Lake Sarez, positions of , geophysical measurements, monitoring and satellite image( GoogleEarth 2011)

landslides©©

Adapted after Gubanova V. – Chernicina E.

- 4 -

Adapted after Gubanova V. – Chernicina E.

Adapted after Gubanova V. – Chernicina E.

10

6

3S

4S

2S

Map explanations

Landslide boondary

Canyon

Sarez Lake

Magnetic measurement

Magnetic and gravimetric measurement

Vertical electrical sounding

Low-frequency measurement

Mise-a-la-masse method

Magnetic, gravimetric and seismic measurement

0 0,5 1,0 km

)

Map of geophysical measurements

N

N

S

S

450

150

120 130110 180

250

150150 180

550

870 1120 mΩ

910 23602280 610

750 600720

2250

1200

220 400

3000

3100

3200

3300

1300

120 - 650 mΩ

m a.s.l.

Debris and loams

Loose material

Loose material - saturated?

Loose material - coarse grained

VES profile 10

Landslide material - no loose

Z (P6)

∆g (P6) ∆g (2S)

Z (2S)

ρ1 (P6)

10

100

-2

0

2

∆g [mGal]

Z [nT]

ρΩ

1 [

m]

0

200

Gravimetric, magnetic and resistivity measurements

Seismic measurements

2,0 km/s

3,53 3,162,7

2800

3000

3200

m a.s.l.

nonprofile measurement

t0 and Θ measurement

N S

Fig. 2 Geophysical measurements on the Usoy dam - landslide

Adapted after Lake Sarez risk mitigation projekt“ ”

- 5 -

that it was possible to determine the total thickness of the slipped materials, i.e. the height of the dam. Further subhorizontal division of the dam body was not successful either by longitudinal or non-longitudinal measurements. The gravimetric measurements interpreted as areal measurements in the area of the “crest” of the dam indicated good possibilities of gravimetry, even in these complicated conditions of measurement (Fig. 3). It was possible to identify two areas with a lack of materials (the green areas) and places, in contrast, with a relative surplus of materials (the orange areas). Particularly the places with a lack of materials are important for the understanding of the behavior of the dam and for the prediction of the behavior for the future. The more extensive gravimetric minimum in the northwestern part of the studied area corresponds to the place described as the “Usoydarya Fan”. It is possible that this fan (dejection cone) is responsible for the whole lack of materials, but it is rather probable that clayey and fine sandy fractions were washed out in this fan and its basement, and even today there is an intensive flow of groundwater in it, including water that can flow in from the Usoy Fault. This whole belt leads into the canyon. The second place with a lack of materials corresponds in all likelihood to those places in which water infiltrates from the lake through the dam body into the canyon. The regional gravimetric field shows reduced values upstream from the dam, but so far no attempt has been made to interpret these anomalies quantitatively. Modern computation methods would certainly made such a procedure possible.

The fourth figure shows the results of the measurement of resistivity and temperature of water in Lake Sarez, in the part adjacent to the Usoy landslide. The results in all places of measurement are similar and the mean values of both the variables are depicted in the left partial graph. First, the resistivity of water moderately rises from the water surface down to a value of about 48 Ωm. Then, a relative rapid drop follows down to a depth of 130 meters where the value of resistivity reaches 20 Ωm; the subsequent drop continues down to the final depth of 350 meters where the lowest value of 14 Ωm was measured. The maximum deviations of resistivity up to 15 Ωm were detected in place T1. The mean temperature of water decreases from the water surface from a value of 9.2°C to 5.2°C at a depth of about 70 meters. Then, the temperature rises to 7.2°C at the final depth that was reached (about 450 m). The maximum deviation – 0.4°C – was detected in place N3. The results obtained

Lake Sarez

0 0,5 1,0 km

Usoy Fault

Sarez Formation

Permo-Triassic

Frontal and secondary massif

Zones of

arching and bulging

After Lim, V.V. et al. 1999

Lake Sarez

Triassicmaterial

Usoydarya Fan

Glacierdeposits

Scarp of UsoyLandslide

Boundary of measured area

∆g > 1.0 mGala

0.0 mGal < g < 1.0 mGal∆ a

-1.0 mGal < g < 0.0 mGal∆ a

-2.0 mGal < g < -1.0 mGal∆ a

∆g < -2.0 mGala

seepage pathway

probable seepage pathway

Gravimetric measurementGeological mapof landslide area

)

Fig 3. Geological map of Usoy dam and result of gravimetric measurement(adapted after Lim, V. and Akdodov, J., 1998 and Lim, V. 1999)

After Lim, V. and Akdodov, J., 1998

- 6 -

clearly confirm that water in Lake Sarez changes from place to place and that greater deviations are in resistivity. To explain this in more detail, it would be necessary to make more measurements in a time series that would describe at least one year. The last illustration from geophysical measurements is from seismic measurements on the Right-Bank landslide. In the profile in Fig. 5, both longitudinal and non-longitudinal measurements were used. In contrast to the Usoy landslide, these measurements yielded interesting and valuable results. It was possible to determine the depth of the shear

plane from both the types of measurement. The velocity in the deepest layer is in full compliance with the velocity in the basement of the Usoy dam. The velocity of seismic waves is surprisingly high and the values detected there are usually measured only at greater depths. It is probable that the increase of velocities is caused by high mechanical stress in the rock mass. In addition to the determination of the base of the fractured rocks, it was also possible to identify a sub-boundary in a slope deformation, which can be described as a different degree of rock fracturing or as different rock moisture. The first two layers are characterized by low moisture and have the character of debris rather than that of solid rock material. The layer above the shear plane has higher velocities, but the growth of velocities is caused by higher moisture rather than by the better character of the slipped material. The lower right part of this figure shows a drilling log of the only borehole at the site. We can see that the lithological description of the borehole has no direct relationship to the results of seismic measurements. A view of the Right-Bank landslide from the opposite slope is given in Figure 6 and its upper left part depicts a section of the slope which can be seen on the skyline of the right bank (a computer composite of two slides).

10 20 30 40 50 ρ Ωw [ m]0

d [m]

100

200

T1

0

100

200

d [m]

2 4 6 8 10 t °[ C]

N3

10 20 30 40 50 ρ Ωw [ m]0

100

200

300

d [m]

400

Mean valuesof water temperatureand water resistivity

Mean valuesMean values

Maximal deviationof water resistivity

Maximal deviationof water temperature

Fig. 4 Water resitivity and water temperarure in Lake Sarez( 197 ) Adapted after Gubanova V. – Chernicina E. 6

2 4 6 8 10 t °[ C]

0,8

1,01,5

4,5

4,5

2,5

1,1

0,6

0,5

1,0

2,1

0,6

1,1

5,0

0,4

0,8

2,5

5,0

0,6

0,6

0,9

1,3

5,5

2,0

4,7

0,6

0,6

1,6

4,3

0,9

1,8

2,1

4,5 5,2

0,8

1,8

2,2

0,3

1,5

2,3

4,0

6,0

0,5

1,1

2,6

0,5

1,0

2,5

6,0 km/s

6,0

5,5

3200

3400

3600

3800

4000

m a.s.l.

Lake

level

0,8 velocity of direct wave [km/s]

boundary velocity [km/s]

boundary from profile measuring

boundary from nonprofile measuring

2,5

loose material

intense rocksly fractured

f rocksractured

intact rocks

Borehole J10

50

100

150

200

loose material

sandstone and siltstone(shale intercalation)

sandstone and siltstone(shale intercalation)

sandstone and siltstone(shale intercalation)

sand

breccia

d [m]

Borehole J1

- 7 -

3. A Proposal of Other Geophysical Work The results of the previous work and the development of instrumentation equipment and processing methods show that at the site it would be possible to come up to a new stage of geophysical measurements. New instrumentation equipment offers the application of new methods, and the implementation of the modern component base into the construction of instruments has significantly reduced the weight of apparatus used. Therefore, it would be possible to move in the terrain more easily with modern equipment, and thus to have the possibility of measuring even those areas which were practically inaccessible with old equipment. Prior to starting new geophysical measurements, we recommend that all available materials about the already accomplished geophysical measurements be found. It is necessary to attempt to obtain these materials not only in Tajikistan, but also in Tashkent and, if possible, also in Moscow. It is necessary to reinterpret previous measurements using new methods of geophysical measurement processing and to evaluate all measurements comprehensively, not only each method separately. As the second step we propose to process satellite images which cover the site. It would be most suitable to obtain images in a broad time span to monitor changes that took place over a given period at the site. For study we consider appropriate using classical images with low resolution, but particularly multispectral images and images with high resolution. It is known to the authors of this paper that there are available archive images from the ASTER satellite (in sixteen periods of time in a range of 2001 – 2008), from the SPOT satellite (with resolution up to 2.5 meters in a range from 2000 to 2008) and from the IKONOS and QUICKBIRD satellites. We propose to use the following methods as new geophysical measurements: • Time-Domain Electromagnetic Exploration to detect subhorizontal boundaries down to a depth of 500

meters. This method can be applied both on the dam of the lake (the Usoy landslide), and also on all slope deformations in the area.

• Microgravimetric measurement with a microgal gravimeter to locate places of low density and thus also to determine predisposed seepage pathways. It would be appropriate to apply this method mainly to the northern part of the Usoy landslide for specifying two potential seepage pathways.

• Measurement of spontaneous polarization using special electrodes to locate seepage pathways on the downstream side of the dam.

• The method of the charge body using special electrodes to locate seepage pathways. • Seismic measurements in the form of seismic refraction and reflection, including the possibility of applying

measurement using transverse waves. • The application of modern 3D sonar devices for the accurate description of slopes below the groundwater

table. And • The use of laser scanners to monitor changes in the ground surface, particularly to observe changes in the

canyon being formed by water seeping through the dam. Scanning of this site from the right and left slopes of the River Murgab would enable a perfect 3D model of the area of interest and a 3D visualization of the chronology of its development to be obtained.

angle of bite

Fig 6. Panoramativ view of Pravoberezhniy landslide

- 8 -

4. Conclusion The results obtained from the preliminary study of the previous geophysical measurements have confirmed the vision of the authors of the usefulness of the application of geophysical methods in the study of the area in the vicinity of Lake Sarez. The study of the archive materials (though incomplete) has shown that the measurements already made have indicated much of the structure of the Usoy landslide itself (the natural dam of Lake Sarez), but also of the other monitored areas. The processing of the results of the previous measurements by new interpretation techniques together with the application of new geophysical measurements in combination with the use of the methods of remote sensing would undoubtedly help supplement the knowledge of the structure of the dam, the position of the shear planes of the individual landslides and possibly also the geological structure of other important sites around the lake. Such knowledge would certainly enable the risks of individual natural processes to be specified more precisely and the critical states to be determined better, thus contributing to the reduction of the risk of the origination of unpredictable events. All these circumstances would increase the safety of the population not only in the basin of the River Murgab, but also in the basins of other rivers through which the water from Lake Sarez travels into the Aral Sea. References: 1. GUBANOVA, V. – CHERNICINA E., Rezultati inzhenerno geologicheskich issledovaniy v rayone

Sarezkogo ozera i dolin rek Murghob i Nartang, 1975 – 1976, Dushanbe, UGSM TSSR, 1976. 2. HORSKY, O. – BLAHA, P., The Application of Engineerin Geology to Dam Constriction, Repronis,

Ostrava, 2011, 3. Lake Sarez risk mitigation projekt, Stucky Consulting Engineers Ltd, Renens, 2003. 4. LIM, V.V. – AKDODOV, Y., Opolzni Sareza, Uzbekgidrogeologiya, Tashkent, 1998. 5. LIM, V.V. et al., Озеро Сарез и экологические проблемы СреднейАзии, 1999.

Ing. Shavkat Abdullaev, PhD. - (born 1948 in Fergana region, Uzbekistan) graduated from the Tashkent Polytechnical Institute, where he wrote a candidate dissertation focused on engineering geology-mineralogy science. He is currently the head of the Hydrogeology and Engineering geology laboratory and is teaching at the School of Geology at National University of Uzbekistan. He focuses on engineering geology, hydrogeology and utilization geophysics methods. He leads independent geotechnical control service in building damp of Uzbekistan. He is a fellow of the consultative committee of European association of geoscientist and engineers (EAGE). He has published 52 works, including 3 monographs and 5 copyright certificates. Ing. Umid Abdullaev - He has over 27 years of professional experience in water and agricultural sectors in Uzbekistan and Aral Sea Basin. He specializes in preparation, design, management and implementation of technical projects and feasibility studies on construction and rehabilitation of I&D systems, dams and pumping stations, water reservoirs, and development the irrigation and drainage strategies and water management projects in Uzbekistan, Turkmenistan, Tajikistan, and Mozambique, Columbia. He has significant experience working on projects in collaboration with the ADB, GEF, EC, WB, and FAO and other. His most significant experience and knowledge was gained in the framework of the GEF/WB Water and Environmental Management Project, the WB Karshi Pumping Cascade Rehabilitation project (2001-2003) and Drainage and Irrigation and Wetland Restoration Project (2005-2009) etc. Assoc. Prof. Dr. Pavel Bláha, D.Sc. – a geophysicist (Faculty of Natural Sciences at Charles University in Prague). His education consists of the following degrees: M.Sc. (1966), RNDr. (1969), CSc. (Ph.D. 1990), Associate Professor (1992) and D.Sc. (1998). In the company GEOtest, a.s., he holds the post of a branch manager. He specializes in geophysical surveys, remote sensing and engineering geology. He has worked not only in the Czech Republic, but as an expert also in other countries of the world, largely for short-term periods, giving expert opinions. He mostly worked in Asian countries. His is the co-author of the book “The Application of Engineering Geology to Dam Construction”. He has published more than 185 works, including 7 mono-graphs. His last work is the book “The Application of Engineerin Geology to Dam Constriction” (co-author). Ing. Akmal Akhmedov – an engineer geologist (Tajik state university). In 1982 courses for increasing qualifications under research institute VSEGINGEO (Moscow). From 1968 to 1990 senior geologist (South hydrogeological expedition under Main geological department Dushanbe), 1990 - chief of hydrogeo-logical group, 1991 – 2001 chief specialist – hydrogeologist of geological division, 2001 – 2011 - chief specialist – hydro geologist of geological division. Ing. Sharifa Khudobakshova, PhD. – a geophysist (Tashkent State Technical University, Faculty of Geology, Institute of Geology of Academy of Republic of Tajikistan – PhD), Certificate Seminar on Field Exploration and Assessment of Natural Risk Reduction Geneva, France, Italy Certificate, Trainers Course on Emergency Situations, Focus Humanitarian Assistance, Seniour Instructor of Geology Department (1998 – 2000), Researcher of Minerals Laboratory Institute of Geology of Academy of Republic of Tajikistan (2000 – 2006), Head of the Department of External Affairs, Head Department of Geology under the Government of Republic of Tajikistan (2006 – 2011), Published over 20 scientific works.