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IJEGE-11_BS-Gavardashvili-&-Ayyub

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Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
63
DOI: 10.4408/IJEGE.2011-03.B-008
THE FIELD INVESTIGATION OF EROSION AND DEBRIS FLOW
PROCESSES IN CATCHMENT BASIN OF THE DURUJI RIVER
G
ivi
GAVARDASHVILI
(*)
& b
ilal
m. AYYUB
(**)
(*)
Georgian Water Management Institute - 60 I. Chavchavadze Avenue - 0162 Tbilisi, Georgia
E-mail: gwmi1929@gmail.com; givi_gava@yahoo.com
(**)
University of Maryland - Center for Technology and Systems Management Department of Civil and Environmental Engineering
College Park, USA - E-mail: ba@umd.edu
INTRODUCTION
Taking into account that the scientific paper con-
cerns the protection of Kvareli population (10-12
thousands) from debris flow on the Duruji River, the
problem described in this paper is very important for
Georgia. In accordance with this purpose and the as-
signment of the President’s authorities (Letter No.
3/29, 20/11/2008), a working group was organized un-
der the guidance of the Institute of Water Management.
The objective of this group is to develop an in-
tegrated general scheme for the protection of Kvareli
population from debris flows using modern methods
and technologies. This scheme will include the follow-
ing: adjusted predictions of erosive - debris flow proc-
esses formed in the bed of Duruji River and, at the next
stage, development of new safe and economic protec-
tive measures using the above-mentioned results; re-
views of possibilities to use the mass of debris in rural
economy on the basis of the appropriate cost-estimate.
The problem is complicated by the fact that the sur-
face of debrisflow fan of the Duruji River is located 10-
12 m above the Mountain (2994 m above sea level), the
northern range of which borders on Dagestan (Russia),
see Fig. 1). The total basin area of the Shavi and the
Tetri Duruji Rivers is equal to 3,08 sq. km, including
the area of 0,25 sq. km) located in subalpine and alpine
zones, and 60-70 hectare located in forest line adjoining
ground surface of the town of Kvareli. This difference
is caused by accumulation of debris flow deposits after
a protective dam was built along the river in 1949.
ABSTRACT
For the effective protection of the population of the
town of Kvareli in Georgia from debris flow formed on
the Duruji River, the critical places on the river-bed of
Duruji, where overflow of debris flow is possible, were
identified. Erosion coefficients of mountain slopes
with debris flowing into the basin of Duruji River,
which establishes links between the class of erosion
and degree of damage of a slope, were explored. Maxi-
mum charges on debris flow of river Duruji in differ-
ent provisions were established, through which, at a
following stage of an ongoing project, anti-debris flow
structures are planned and designed. Using the theories
of reliability and risk, probability distributions of the
maximum charges of debris flow formed on river Du-
ruji were examined including the suitability of using
the Weibull probability distribution.
The reliability of new springboard type debris flow
protection structures and associated risk profiles in the
case of joint and separate dynamic and statistic influ-
ences of debris flow on the structures were assessed.
Results from this investigation enabled us to predict
effectively erosive-debris flow processes in the river-
bed of Duruji, and introduce new ecological measures
engineered to ensure the effective protection of the
population of the town of Kvareli in Georgia and con-
tiguous territory of the Duruji River from debris flow.
K
ey
words
: Duruji River, kvareli Town, erosion coefficient,
debris flow.
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G. GAVARDASHVILI & B.m. AYYUB
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
catchment basin of the Duruji River is subdivided into
the following parts: 1. shale stratum; 2. strata with in-
clusions of clay-shales and sandstones, and: 3. quater-
nary sediments.
Climate. The average annual temperature of the
Duruji River basin varies within +12.2-14 oC, is this
12.2 to 14 mm, the average Soils. Generally, the fol-
lowing six types of soils are distributed in the basin
of the Duruji River: cinnamonic forest soils, brunisol,
outwashed soils (slopes), soils of mountain-forest-
valleys, light chestnut soils, which can be observed
generally in alpine and subalpine zones, proalluvial
and deluvial soils (G
avaRdasHvili
& C
HakHaia
, 2002).
Plants. The whole area in the catchment basin
of the Duruji River is subdivided in the following
sequence: forests 76% (0.0066 sq. km), without for-
ests 4.3% (0.00039 sq. km), summer pastures 16 %
(0.0014 sq. km), rocks 4.3 % (0.00033 sq. km).
GENERAL DESCRIPTION OF THE CATCH-
MENT BASIN OF THE DURUJI RIVER
The Duruji River can be considered as one of the
most active rivers with debris flow processes among the
mountain rivers comprising the catchment basin of the
Southern Caucasus (Georgia, Azerbaijan, and Armenia).
Field investigations during 2000 to 2009 imple-
mented in the catchment basin of the Duruji River re-
vealed that the ecologicalconditions are disastrous in
the basins of the Tetri and the Shavi Duruji.
It is well known that the bed of Shavi Duruji is erod-
ed because of the Shavi Mountain (2200 m above sea
level), and the bed of Tetri Duruji is eroded because of
the Southern range of the Pokhalo (G
aGosHidze
,1970;
t
seReteli
, etc. 2001; G
avaRdasHvili
, 2003).
The total area of the catchment basin of the Du-
ruji river including its debris flow cone is equal to 116
km
2
, among which the area of debris flow cone by it-
self is equal to -36 km
2
.
The length of debris flow cone from the mouth
of the Duruji River up to the so called Kherkheulidze
structure is equal to 8.0 km, and the length of the
river in the gully is equal to 18 km. Thus, the total
length of the river is equal to 26 km, and its average
gradient is i=0.222.
The average width of the catchment basin of the
Duruji River is about 4.3-4.5 km, and the maximum is
equal to 6.5-7.0 km (G
aGosHidze
, 1970, G
avaRdasH
-
vili
& C
HakHaia
, 2002).
Geology. The catchment basin of the Duruji River
is subdivided into two geographical parts: the Main
Caucasian Range and Alazani Valley (G
aGosHidze
,
1970). In accordance with the lithological section, the
Fig. 1 - The catchment basin of the Duruji River
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THE FIELD INVESTIGATION OF EROSION AND DEBRIS FLOW PROCESSES IN CATCHMENT BASIN OF THE DURUJI RIVER
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
65
basin of the Duruji River was covered by the avalanche
(5-6 m thickness, 150 m long) slipped from the gully
of the Tsipel Gori River (the left tributary of the Shavi
Duruji River) (see Fig. 4). In accordance with the lon-
gitudinal profile of the Duruji River, the gradient of this
section is equal to 17°, the width of channel -4.6 m, and
the depth of water flow -0.32 m (G
avaRdasHvili
, 2003;
G
avaRdasHvili
& C
HakHaia
, 2002).
The field surveys implemented in the catchment
basins of the Shavi and the Tetri Duruji Rivers have
produced a conclusive evidence that the ecologi-
cal conditions of the mentioned areas as disastrous,
which requires immediate implementation of appro-
priate measures.
To assess the erosive processes for the gullies with
active erosive - debris flow processes in the catchment
basin of the Duruji River,
the erosion coefficient (E) has been calculated on
the basis of dependence obtained as a result of field
works and interpretation of aerial and satellite images
(G
avaRdasHvili
et alii, 2006):
E = [0,58 + 1,40 (F
1
/ F
0
)] · (t / T)
0,21
(1)
PREDICTION OF EROSIVE - DEBRIS
FLOW PROCESSES IN THE BED OF THE
DURUJI RIVER
Implemented field investigations confirm that in
the future the power of debris flow formed in the Duruji
riverbed will not be only under the influence of erosive
and landslide processes, but also under the influence of
avalanches. During the expedition, we have noticed a
big boulder of 63.1 tons (see Fig. 2), which has been
moved downwards for the distance of 200 m as a result
of flood and average debris flow in the Shavi Duruji riv-
erbed during the period of 2 months. The implemented
investigation revealed that the above-mentioned boul-
der belongs to the catchment basin of the Savepkho-
Gori river (the left tributary of the Duruji River).
The tectonic break of mountainous strata has
been observed on the Pokhalo Mountain (springs of
the Tetri Duruji River), 2990 m above sea level (see
Fig. 3). In the future, this break can activate annual
temperature is - 3.7 oC in winter, and the highest tem-
perature is +25 oC in summer.
The average annual quantity of precipitations in
the Duruji River basin is equal to 960 mm, and 901
mm in Kvareli (G
avaRdasHvili
, 2002). The maximum
quantity precipitations is observed in spring-summer
periods (May-June).
In accordance with the data of meteorological sta-
tion the maximum quantity of precipitations (1/4) can
be observed in May-June.
landslide processes, which can be considered as
the initial stage intensify the erosive-debris flow proc-
esses (G
avaRdasHvili
& C
HakHaia
, 2002).
The influence of avalanches can be added to the
erosive-debris flow and landslide processes in the basin
of the Duruji River. On the 22 June 2001, the catchment
Fig. 2 - Boulder (63.1 ton) in the Duruji Riverbed
(Photo G.G
AvArDAShvili
)
Fig. 3 - Tectonic fault zone, Pokhalo Mountain. 22
June, 2001 (Photo G.G
AvArDAShvili
)
Fig. 4 - Avalanche in the Shavi Duruji valley, 2001 (Photo
G.G
AvArDAShvili
)
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G. GAVARDASHVILI & B.m. AYYUB
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
collected data, and we found that their error varies
between 5-20% in case of 0.95% probability, which
are considered as satisfactory values for hydrologi-
cal calculations.
To predict the quantity of debris mass collected
in the catchment basin of the Duruji River, we have
measured general features of mass slid from the moun-
tainous slopes in the Noga riverbed. These features are
as follows: geometrical dimensions of talus train, slope
angles of solid fractions on the talus train and internal
friction angles, average diameters of fractions etc.
Fig. 4 shows general view of eroded slopes in 700
m from Shavi Klde near the upper reaches of the Shavi
Duruji River, and Fig. 5 shows the erosional slope of
Pokhalo mountain in the upper reaches of the Tetri
Duruji river, 2800 m above sea level.
The results of granulometric analysis concern-
ing the samples of solid composition obtained from
the talus train of the Duruji river are given in Tab. 2
(G
aGosHidze
, 1970). The chemical analyses of col-
loidal mass needed to use debris mass in production
(G
avaRdasHvili
& C
HakHaia
, 2002) are given in Table
3 (value of chemical elements is given in %).
where, F
1
- erosive area (km
2
) in the catchment basin
of the river, F
0
- area (km
2
) of the whole catchment
basin, t - time interval surveyed (year), T - total obser-
vation period (in our case T=30 years).
(1) - limit dependencies are as follows:
0.061 ≤ (F
1
/F
0
) ≤ 0.24 ; 0.1 ≤ (t/T) ≤1.0
(2)
The values of erosion coefficient for the moun-
tainous slopes of the Duruji river basin are calculated
by the dependencies (1) taking into account the appro-
priate values of damage rate given in Table 1.
The frequency of ravines and flumes observed in
some sections of so called “Black Mountain” in the
upper reaches of the Duruji River (2002) is equal to
15-20 m. In accordance with the classification of Prof.
R. Morgan (m
oRGan
& H
ann
, 2001), this value is ap-
propriate to the 7
th
class of erosion with the intensity
of erosion more than 500 (t/ha) per year.
As about the association (Table 1) between the
erosion class and the erosion coefficient, it has been
calculated in accordance with the scale of Prof. R.
Morgan (m
oRGan
& H
ann
, 2001)].
To assess the stability of the Duruji riverbed, we
have measured the widths of Tsotskhali section (b) and
Noga channel (B), depths of water flow (h), gradients of
the riverbed (a) and flow velocities (V). Then, we have
measured the discharges of water flow (Q
0
). The number
of statistical measurement is equal to 177 points.
The empirical values have the following forms:
(h / b) = 0,3 (a)
-0,62
(3)
(b / B) = 0,001(a )
2,11
(4)
Limitations on the dependencies (3) and (4) are
as follows:
To assess the reliability of dependences (3),
the resulting values have been compared with the
Tab. 1 - Erosion coefficient and erosion class of mountainous slopes in the catchment basin of the Duruji River
(5)
Fig. 4 - Erosional Slopes of Shavi klde. 21 June, 2001
(Photo G.G
AvArDAShvili
)
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THE FIELD INVESTIGATION OF EROSION AND DEBRIS FLOW PROCESSES IN CATCHMENT BASIN OF THE DURUJI RIVER
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
67
The coefficient of variation of debris discharge is
equal to (a
yyub
, 2003):
The coefficient of asymmetry was calculated on
the basis of the following dependences:
C
S
= 2 · C
V
= 2 · 1,128 = 2,256
Using the values obtained, we have calculated debris
discharges of different provisions of the Duruji River.
These values are given in the Table below (see Tab. 4)
To assess field data, which will allow us to predict
maximum debris discharges of different provision for
the Duruji river; we have used the following empirical
dependence (G
avaRdasHvili
et alii, 2006):
Q
max
= A · (34 + 400 · i) · F
0,61
(m
3
/sec)
(9)
where, A - coefficient, which is given with the coeffi-
cient of discharge in Table 5; i - average gradient of the
Duruji River, which is equal to i=0.222; F - area of the
catchment basin of the Duruji River, F = 80.0 sq. km;
As for the mass slid from the mountainous slopes
in the catchment basin of the Shavi Duruji River, it is
equal to 300 000 m
3
according to the data of June-July,
2001. This value can be considered as an average one
for the conditions of this channel.
Thus, the field investigations implemented in
summer (2001-2009) in the catchment basin of the
Shavi and the Tetri Duruji Rivers revealed that
the condition of erosion processes on the moun-
tainous slopes are disastrous and, in some sections, it
can be considered as equal to the 7
th
class of erosion.
DETERMINATION OF MAXIMUM DI-
SCHARGES OF DIFFERENT PROVISION
FOR DEBRIS FLOW FORMED IN THE
DURUJI RIVERBED
To determine maximum discharges of different
provision for debris flow formed in the Duruji Riv-
erbed, we have used scientific literature (G
aGosHidze
,
1970; G
avaRdasHvili
, 2003; G
avaRdasHvili
& C
Ha
-
kHaia
, 2002; М
iRtskHoulava
, 1998; n
atisHvili
&
t
evzadze
, 1996; t
akaHasHi
, 1994) and statistic line
developed and restored by the author on the basis of
data obtained in hydrometeorological observatory.
The accumulative value of relative maximum dis-
charge for the debris flows passed in the Duruji River-
bed (1899-1999) is equal to = 7,856 (m
3
);
the statistical value based on the field observation is
equal to N = 46 points.
The average value (Q
i
/ Q
max
) of relative discharge
for the debris flow is equal to:
Fig. 5 - Erosional Landslide Slope of Pokhalo
Mountain. 2001 (Photo G.G
AvArDAShvili
)
Tab. 2 - Mechanical composition of debris mass obtained on the
Debris Flow Cone of the Duruji River
Tab. 3 - Chemical analysis of colloidal mass
of the Duruji River
(6)
(7)
(8)
Tab. 4 - Discharges of Different Provisions of the Duruji River
Tab. 5 - Association between the coefficient
(A) and the discharge provision (P%)
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G. GAVARDASHVILI & B.m. AYYUB
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
We have determined that to predict the maxi-
mum discharges of the Duruji river, the values calcu-
lated on the basis of dependences (9) are correspond
more closely to the data of natural debris discharge
than to the values calculated on the basis of Weibull
formula (see Table 5).
The results were compared with the method-
ology developed by Acad. Tsotne Mirtskhulava
iRtskHoulava
. 1998), who determined the pattern
of change in maximum debris discharges using the
mathematical simulation, especially, probability theo-
ry. The coincidence between them is satisfactory.
Tab. 6 - Relative Values of Debris Dis-
charge per appropriate Intervals
(10)
The average square error of maximum debris discharge has been calculated on the basis of the following
dependence (a
yyub
, 2003):
The data needed to plot histogram are given in Table 6.
The mathematical expectation is determined on the basis of the following formula (a
yyub
, 2003; G
avaRdasH
-
vili
& C
HakHaia
, 2002):
(11)
The histogram of values relative to the maximum discharges of the Duruji river and the curve of appropriate
theoretical distribution are given on Fig. 6.
The Weibull distribution (a
yyub
, 2003) appropriate to the curve given on Fig. 6 is as follows:
f (Q
i
/ Q
max
) = 0,035 · (Q
i
/ Q
max
)
-0,82
· exp [-0,192 · (Q
i
/ Q
max
)
0,18
]
(12)
Fig. 6 - Histogram of maximum debris
discharge (1) and curve of appro-
priate theoretical distribution (2)
If we calculate the maximum discharges of the Duruji River using Weibull distribution, the reliability of val-
ues obtained on the basis of dependence (12) should be calculated by the following formula:
Solving the equation (13) we receive the following value P (Q
i
/ Q
max
) = 0,549, and the non-performance
probability is as follows:
R = 1 - P (Q
i
/ Q
max
) = 1 - 0,549 = 0.461
(13)
(14)
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THE FIELD INVESTIGATION OF EROSION AND DEBRIS FLOW PROCESSES IN CATCHMENT BASIN OF THE DURUJI RIVER
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
69
the above-mentioned statistical line we receive em-
pirical dependence, which allows us to calculate the
volume of debris flow transported by debris flow in
the Duruji riverbed (w).
The mathematical expression is of the following type:
w = 0,138 · T
1,52
· Q
max
0,73
(m
3
)
where, T - travelling time of debris flow in the riverbed;
Q
max
- maximum discharge of debris flow (m
3
/ wm).
Limitations on dependencies (15) are as follows:
180 ≤ T ≤ 2160 (sec)
100 ≤ Q
max
≤ 2000 (m
3
/ sec)
Using the dependencies (15) we have calculated
PREDICTION OF DEBRIS MASS TRAN-
SPORTED IN THE DURUJI RIVERBED
To predict debris mass transported by debris
flow of the Duruji River, we have used the results
of field surveys implemented in the summer of
2001-2009 and the scientific literature published
during the recent period of time (G
aGosHidze
,
1970; G
avaRdasHvili
, 2003; n
atisHvili
& t
evza
-
dze
, 1996; t
seReteli
et alii, 2001).
The statistical line of debris flows in the Duruji
riverbed revised and, in some cases restored, is pub-
lished in the paper (G
avaRdasHvili
, 2003); processing
(15)
(16)
Tab. 7 - Coincidence of Debris Mass transported by Debris flow of the Duruji River
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G. GAVARDASHVILI & B.m. AYYUB
70
5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
the values of debris mass (w) transported by debris
flow in the Duruji riverbed, which were compared
with the natural data; the percentage indices of their
coincidence are given in Table 7).
Tab. 7 comparison between the values of debris
capacity transported by the debris flow in the Duruji
riverbed and the data calculated by formula (15) gives
us errors of 0.2 - 40 %, which can be considered as
satisfactory for hydrological calculations.
CONCLUSIONS
The following general conclusions and recom-
mendations can be drawn on the basis of field inves-
tigations implemented in the catchment basin of the
Duruji River (2001-2009) and scientific literature:
• To provide effective protection of Kvareli popu-
lation against debris flow in the Duruji riverbed, we
have determined those critical sections, where debris
flow can break the riverbed;
• We have studied erosion coefficients for the
mountainous slopes of debris tributaries sliding in
the catchment basin of the Duruji River. These coef-
ficients allow us to determine the coincidence between
the class of erosion and the damage rate of slopes;
• We have determined the maximum discharges
of different provision regarding the debris flow of
the Duruji river, which allow us to design structures
against debris flows;
• Using the theory of reliability and risk, we have
determined distribution law for the function of maxi-
mum debris discharges formed in the Duruji riverbed,
which has a form of Weibull;
• We have obtained empirical dependence, which
allow us to calculate the capacity of debris mass trans-
ported by debris flow in the Duruji riverbed;
• The results obtained in ceramics plant regarding
the chemical analysis of debris mass (10 - 20 M m
3
)
collected in the Duruji riverbed allow us to use Du-
ruji debris mass in construction works (facing slabs,
bricks, mortar, glass making etc.), in agriculture (in-
crease in output of Kindzmarauli wine, increase in sta-
bility of farmlands located on the mountainous slopes,
which are under the influence of erosion processes), in
production of ceramics and other products.
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yyub
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M.C. (1970) - Debris flow processes and their prevention measures. Tbilisi, 385(in Russian).
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avaRdasHvili
G., s
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inG
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ann
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atasHidze
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