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Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
417
DOI: 10.4408/IJEGE.2013-06.B-40
PREDICTION OF FLOODED TERRITORIES
IN CASE OF POSSIBLE BREAKDOWN OF THE SIONI EARTH DAM
G
ivi
GAVARDASHVILI
(*)(**)1
(*)
Water Management Institute of Georgian Technical University 60, Ave. I. Chavchavadze, 0162, Tbilisi, Georgia
E-mail: givi_gava@yahoo.com - Phone: + 995 32 2 224 094
(**)
Ecocenter for environmental Protection Varketili 3, 2 m/r, bull. 29-a, App. 17, 0163, Tbilisi, Georgia
E-mail: ecocenter1985@gmail.com - Phone: + 995 32 2 796 796
Among the various natural reasons causing
floods, particular attention should be paid to the faults
or knocking down of waterworks facilities, which on
their turn can be caused by different natural calami-
ties, such as earthquake, as well as by the accidents of
outdated hydraulic structures. Dam breakdown is also
possible through terrorist acts.
In practice, the reliability of dams of different des-
ignations has been the subject of interest for the man-
kind since the ancient times, evidenced by the water-
retaining facilities of different heights built in Babylon,
China, Egypt and Italy several thousand years ago.
The specialists have considered the little depth of
the material laid in a dam foundation as the main rea-
son for dam failures with the second most widespread
reason being the overloading of an earth dam above
the acceptable level and so on.
Besides, studying the effect of seismic impact is
one of the central issues when considering the stabil-
ity of slopes. Earthquakes with the magnitude of over
5,5 are capable of causing the landslide of natural and
artificial slopes.
For instance: the 1920 earthquake caused more
than 100.000 victims; the Alaska earthquake in 1964
with large-scale destruction; the landslide in the ba-
sin of Vajont arched Dam in Italy in 1963 having
taken away the lives of 2.300 people (G
avardashvili
,
2010a) and the landslide in Philippine in February
2006 with 2.000 victims.
Below, we report some dam failures in the world with
ABSTRACT
1
In order to carry out a computer simulation of a
flood originating in the case of a possible breakdown
of the Sioni earth dam, the author has re-worked the
algorithm of the Volna-2”, which allows, in the case
of a possible breakdown of the dam, to calculate the
wave velocity, the run-out distance according to the
topography of river.
In the case of a possible breakdown of the Sioni
earth dam the population of the Iori valley as well
as the areas adjoining the Iori River comes under
great flooding.
As to the spread of the waters it occurs in the
north - eastern and south - western directions.
K
ey
words
: earth dam, imitation of a flood, prediction,
break down
INTRODUCTION
Floods, with their recurrence, frequency and
generated rank are the first among the natural calami-
ties in the world. By the UN data, in the past century
(1900-2000) floods took away the lives of approxi-
mately 10 million people in the world if not talking
about the damages caused by them (G
avardashvili
et alii, 2009).
1
Experience within the NATO SfP 983833 project entitled “Risk-
Based Security Analysis of the Hydraulic Systems in the River
Network in the South Caucasus Regions (Armenia, Azerbaijan
and Georgia)”
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G. GAVARDASHVILI
418
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
ple died (G
avardashvili
, 2010b).
The problem is further complicated by the impos-
sibility of making an accurate forecast or arresting of
a natural calamity - wreckage of a dam and its result-
ant flood. Reduction of the damages and improvement
of the population safety need accurate forecasting of
floods and risk-factor assessment of natural calami-
ties, as well as continuation of the diagnostic and in-
tensifying the scientific-practical studies of the out-
dated hydraulic structures.
As it is known, an accurate forecast of flood is
possible if the data and characteristics of hydrographic
networks, topography of the study area, natural bar-
riers and factors capable of changing the hydrologi-
cal regime, as well as technical data of the outdated
hydraulic structures in the area are known in advance.
The cadastre of reservoirs, carried out in Geor-
gia in the 1960-1980, recorded 64 large and small
reservoirs on the entire territory of the country. As is
known, along with the basic economic purpose of res-
ervoirs, special role is assigned to dams as one of the
means of regulating natural disasters, including floods
and freshets.
Scientific observation of the world climate has
shown that rise of temperature is noticeable on our
planet, facilitating intensive melting of glaciers,
which in turn is one of principal causes of the forma-
tion of floods, freshets and many different types of
instabilities.
In the modern world a frame treaty based on
risk analysis is given special attention by scientist
for the analysis of various types of hazard (a
yy
-
ub
, 2003; G
avardashvili
, 2010b; G
avardashvili
,
2011a; G
avardashvili
, 2011c; G
velesiani
et alii,
2003) for by this method not only the expected risk
is assessed but it becomes possible to plan measures
for averting or mitigating the expected catastrophe.
With account of all these factors, loads are gradually
increasing on water-management facilities, includ-
ing obsolescent dams. Account should also be taken
of the studies started in 1969 by Acad. Tsotne Mirt-
skhoulava (M
irtskhoulava
, 1993; M
irtskhoulava
,
2003) that are related to the so-called “aging” of
dams, which reduces the reliable work of dams and
raises the probability of the risk of their collapse.
To assess the damages caused by the destruction
of Sioni earth dam (Georgia) (Fig. 1) and analyze the
expected results of hydrodynamic calculations, by con-
great numbers of human victims (G
avardashvili
, 2011).
• In 1864, the failed Bradfield earth dam in the
USA. The dam upstream wall was faced with con-
crete tiles, and clay-loamy ground was placed in
the dam center. The dam accident took away the
lives of 239 people.
• On May 31, 1889, the 92-metre-high South Fork
earth dam in the State of Pennsylvania (USA) fai-
led and took away the lives of 2.500 people.
• On February 22, 1890, the 33,6-metre-high em-
bankment dam in the State of Arizona (USA) fai-
led and taking away the lives of 129 people.
• On April 27, 1895, the 22-metre-high Bouzev
embankment dam failed in France, and 156 peo-
ple died.
• On September 30, 1911, a concrete dam near the
city of Austin (State of Pennsylvania, USA) failed
taking away the lives of 100 people.
• On August 13, 1935, a 16,5-metre-high concrete
dam in the village of Zerbino (Italy) failed cau-
sing the death of over 100 people.
Dam accidents also happened in the former Sovi-
et Republics, but due to the Soviet politics, the cases
of accidents were never published. Therefore, the in-
formation about the number of victims is unknown.
For instance, in 1955, an accident happened at Gorki
hydroelectric power plant dam; in 1956, there hap-
pened an accident with Luzhskyi dam (Leningrad
oblast), in 1958, an accident happened with Irkutsk
dam and so on.
Some of the most recent failures are given hereafter:
• The failure of the earth dam in the basin of the
Tangjiashan River caused by the earthquake of
2008 in China (Sichuan Province), thousands of
hectares of the area got flooded because of the
ground block-up in the riverbed.
• The failure of an earth dam (built in 1930) in the
city of Jakarta in March of 2009 took away the
lives of over 20 people.
• The failure of Saino-Shushenskyi dam in Russia
on August 17, 2009, which took away the lives of
17 people (the newspaper “Vzgliad”) and so on
(G
avardashvili
et alii, 2009).
As for Georgia, there is only one accident of an earth
dam happened on the night of May 14, 1987, in set-
tlement Tskneti, near Tbilisi. The dam height was 11.9
m. The catastrophe happened 30 years after the dam
was built as a result of a 3-hour-long downpour. 3 peo-
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PREDICTION OF FLOODED TERRITORIES IN CASE OF POSSIBLE BREAKDOWN OF THE SIONI EARTH DAM
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
419
tion sites lying downstream the hydraulic-engineering
scheme, as well as the duration of the passage of the
wave through the indicated sites (T), equal to the sum
of time of rise of levels (T
r
) and time of fall (T
fl
) or the
difference between (T
t
and T
cr
).
The following are the initial data necessary for
calculations of the parameters of the breach wave
(s
hterenlikht
, 1984):
- The capacity of the reservoir, W
R
:
where H
R
- is the depth of the reservoir at the dam (m);
S
R
- is the area of the surface of the reservoir (area of
flowage) m
2
;
- Slope of the river bottom:
where h
G
- is the depth of the river downstream the
dam; М - is the parameter describing the form of river
cross-section, assumed according to Fig. 3; B
W
- aver-
age width of the river at the height h
G
; h - water river
depth in downstream (s
hoiGu
, 1998).
In order to predict the catastrophe of the Sioni
earth-fill dam, the algorithm of the "Volna-2" program
was re-worked, allowing calculating the rate of the
wave in case of collapse, the run-out distance and,
sidering the hydro-geological and morphological char-
acteristics, the calculation models for the considered
area have been designed. As for the assessment of the
risk-factor of a natural calamity, this was done by con-
sidering various cases of different degrees of damage of
hydraulic structures (0.25%, 0.50% and 1.0%).
The article considers a concrete example, in par-
ticular, the case of the total wreckage of Sioni earth
dam with the destruction coefficient of 1.0%.
METHODOLOGY FOR ESTIMATING
THE LOSSES IN THE CASE OF AN ACCI-
DENT AT THE SIONI EARTH DAM
The main striking factors of catastrophic flooding
are: breakthrough wave (height of the wave, rate of
movement) and the duration of flooding.
The breakthrough wave is one formed at the front
of the water rushing through the breach. It has a con-
siderable height of crest and rate of movement, pos-
sessing a great destructive force and energy.
From the hydraulic point of view, a breach wave
is a moving wave which, unlike wind waves rising
on the surfaces of large reservoirs, has the capacity
to transport in the direction of its movement large
masses of water. Therefore, a breach wave should be
considered as a definite mass of water moving down-
stream the river and continuously changing its form,
dimensions and rate. A longitudinal section of such
wave is schematically shown in Fig. 2.
The breach wave is the principal striking factor
for the destruction of a hydraulic-engineering struc-
ture, hence in order to determine the engineering situ-
ation it is necessary to define its parameters: the height
of the wave (H
w
), depth of the stream (H), rate of
movement and time of arrival at various characteristic
points of the wave (front, crest, tail) at the calcula-
Fig. 1 - General view of Sioni earth dam upstream wall
Fig. 2 - Diagrammatic longitudinal section of a breach wave
(1)
(2)
Fig. 3 - Values of the parameter M related to the form of
the cross-section of the river-bed
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G. GAVARDASHVILI
420
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
Tab. 1 - Initial data on the hydro scheme
where W
R
- is the reservoir capacity; A - is the co-
efficient of the reservoir curvature; for approximate
calculation it is assumed to equal 2; µ - is the pa-
rameter characterizing the shape of the river-bed;
В
i
- is the width of breach, m; H - is the depth of the
reservoir in front of the hydroelectric scheme.
3. Determination of the time of arrival of the breach
wave to the 1
st
site
where L
1
- is the distance of the 1st river section
(km); V
1
- is the rate of movement of the breach
wave at the 1st section (km/h).
4. Determination of the arrival of the breach wave at
the 2
nd
and site
where, L
2
- is distance from the 1
st
to the 2
nd
site,
in km; V
2
- is the rate of movement of the breach
wave at the 2
nd
section, in km/h.
To obtain the parameters of the breach wave at the sub-
sequent sites, an analogous method is used. According
to the results obtained of the breach wave at all sites, a
graph of movement of the breach wave is built.
FORECASTING SIONI EARTH DAM AC-
CIDENT BY CONSIDERING THE RISK-
FACTOR
Sioni water reservoir is located near the village of
Sioni, Tianeti Region (70 km from Tbilisi), in the val-
ley of the river Iori. An earth fill dam is built across
the river Iori, at an elevation of 415 m above sea level,
with its upstream wall faced with concrete tiles. Data
of the dam are reported in Tab. 1 (h
ydroelectric
s
ta
-
tions
of
G
eorGia
, 1989).
most importantly, the geometrical dimensions of the
inundated territory.
The initial data were divided into two parts: first -
constant values, and second - variables. Parameters taken
into consideration in constant values do not depend on
any condition; as to variable values, they depend on the
degree of the destruction of the dam, flood, and so on.
The width of the river is taken from a topographi-
cal map (1:200.000). As to the number of points, they
should not exceed 3 points on one side of the river axis
(in all 6 points on both sides).
To determine the area of the flooded territory the
number of sections from the dam should not exceed 8
sections, the distance between which should be given
on the topographical map in advance.
The rate of wave (V) flooding in the tail-race of
the structure is calculated by the following formula
(G
avardashvili
, 2010
b
; G
avardashvili
, 2011
a
):
V
=
V
0
(H
1
/
H
0
)
2/3
where V
0
- is the rate of water in the river in the tail race
of the structure (m/s); H
0
- is the height of water in the
river in the tail-race of the dam (m); H
1
- is the height of
water in the river at the time of flooding (m).
The degree of destruction of the dam (E
P
) is deter-
mined by the following relation (s
hoiGu
, 1998; s
hter
-
enlikht
, 1984):
E
p
=
F
w
/
F
0
where F
w
- is the area of the collapse of the bank (m
2
);
F
0
- is the area of the surface (m
2
); in our case E
P
= 1.0.
In addition to the above, considered in the algo-
rithm are: the height (m) of river bank, the number of
section along the river, the distance between the sec-
tions (km), width of the river bed (m), the rate of the
water stream in the river bed (m/sec); the width of bed
of the river (m), etc.
ORDER OF CALCULATIONS OF THE PA-
RAMETERS OF THE BREACH WAVE
1. Determination of the height (H
BI
) (s
hoiGu
, 1998):
where H - is the depth of the reservoir at the dam
(m); h
G
- is the river depth downstream the dam (m).
2. Determination of the time passage of the breach
wave through the site of the destroyed dam (time of
complete emptying of the reservoir; s
hoiGu
, 1998):
(3)
(4)
(5)
(6)
(7)
(8)
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PREDICTION OF FLOODED TERRITORIES IN CASE OF POSSIBLE BREAKDOWN OF THE SIONI EARTH DAM
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
421
The volume of Sioni water reservoir is about 433 x
10
6
m
3
.
Aiming at specifying the flooded area as a result of a
possible accident of Sioni dam, the cross-sections near
the settled areas were selected (Fig. 4).
Distances and arrival times are given in Tab. 2.
By considering the sections selected across the
river Iori, hydraulic and hydrological characteristics
of Sioni earth dam, volume of the water reservoir and
topographic characteristics of the river, “Volna-2”
program algorithm was used (s
hoiGu
, 1998) and the
following values were acquired: the geometry of the
flooded area on the right and left sides off the river,
wave speed, depth of water, etc. in case of an accident
of Sioni dam across the river Iori.
The major hydraulic and hydrological characteris-
tics of the wave in case of an accident of Sioni dam are
given in Tables 3 and 4, and the graphs of the flooded
cross section are referred to in Figs 5-13 showing the
data of Sioni dam accident with the degree of the facil-
ity destruction of E
p
=
1,0% provision.
The results obtained for the case of breach of
Sioni dam are given in tables (see Tab. 2), while the
geometric dimensions of the territories flooded in the
river bed and adjoining territory are given in Tables
(see Tabs 3 and 4). The transverse view of Sioni dam
at the initial section is shown in Fig. 5-13.
The calculated geometry of the flooded area was plot-
ted on the map shown in Fig. 14.
Thus, by considering the degree of destruction of
Sioni earth dam (E
P
=
1,0 %), have established the ge-
ometry of the water-flooded areas in the bed of the
river Iori and its adjacent area, where is possible water
mass flooding.
Fig. 4 - Location of the area (a) and of the estimated
cross-sections (b)
Tab. 2 - Statistical and calculated indices of wave
Tab. 3 - Data calculated for the case of breach of Sioni dam
Tab. 4 - Data calculated for the case of breach of Sioni dam
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G. GAVARDASHVILI
422
International Conference Vajont 1963-2013. Thoughts and analyses after 50 years since the catastrophic landslide Padua, Italy - 8-10 October 2013
CONCLUSION
• Based on the published scientific literature, a
risk analysis-based upon CAPRA model (a
yyub
,
2003) for the analysis of different hazards. The
analysis of the statistical data of dam accidents
Fig. 5 - Initial section of Sioni hydro scheme
Fig. 6 - Section N1 - v. Nakalakari.
Time of arrival of wave front: 8 min; time of flood-
ing: 117 min; max. height: 22 m; max rate: 10 m/s;
mark of under flooding sea level: 1011 m a.s.l.
Fig. 7 - Section # 2 - v. Bochorma.
Time of arrival of wave front: 18 min; time of flood-
ing: 205 min; max. height: 21 m; max rate: 11 m/s;
mark of under flooding sea level: 961 m a.s.l.
Fig. 8 - Section # 3 - v. Sasadilo.
Time of arrival of wave front: 29 min; time of
flooding: 279 min; max. height: 12 m; max rate: 7
m/s; mark of under flooding sea level: 891 m a.s.l.
Fig. 9 - Section # 4 - v. Paldo.
Time of arrival of wave front: 40 min; time of
flooding: 340 min; max. height: 10 m; max rate: 7
m/s; mark of under flooding 844 m a.s.l.
Fig. 12 - Section # 7 - v. Mughalno.
Time of arrival of wave front: 70 min; time of
flooding: 474 min; max. height: 6 m; max rate: 5
m/s; mark of under flooding 715 m a.s.l.
Fig. 13 - Section # 8 - v. Sartichala.
Time of arrival of wave front: 77 min; time of
flooding: 499 min; max. height: 5 m; max rate: 4
m/s; mark of under flooding 694 m a.s.l.
Fig. 10 - Section # 5 - v. Ujarma.
Time of arrival of wave front: 59 min time of flood-
ing: 423 min; max. height: 8 m; max rate: 7 m/s;
mark of under flooding 766 m a.s.l.
Fig. 11 - Section # 6 - v. Khashmi.
Time of arrival of wave front: 63 min; time of
flooding: 443 min; max. height: 7 m; max rate: 6
m/s; mark of under flooding 737 m a.s.l.
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PREDICTION OF FLOODED TERRITORIES IN CASE OF POSSIBLE BREAKDOWN OF THE SIONI EARTH DAM
Italian Journal of Engineering Geology and Environment - Book Series (6) www.ijege.uniroma1.it © 2013 Sapienza Università
Editrice
423
worldwide is of particular interest allowing fo-
recasting the risk of possible catastrophes of old
earth dams in Georgia.
• By considering the degree of destruction of Sioni
earth dam (E
P
=
1,0 %), the geometric sizes of the
water-flooded areas in the bed of the river Iori and
its adjacent area were specified by considering the
major dynamic and hydrological characteristics of
a wave and topographic and time factors.
• Thus, the introduction of the gained results in
practice allows to effectively forecast the pre-
ventive measures for the population, which, if
realized, will significantly reduce the number of
possible human victim in case of the wreckage of
Sioni earth dam.
Fig. 14 - Layout of the areas flooded as a result of Sioni
earth dam accident (scale 1: 1 000 000)
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