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Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
913
DOI: 10.4408/IJEGE.2011-03.B-099
FORECAST OF DEBRIS FLOW HAZARD IN
THE NORTHERN SIDE OF THE GREATER CAUCASUS
O.A. k
umukova
, I.B. s
eynova
, A.H. a
dzHiev
, N.V. k
ondRatJeva
(*)
(*)
High-Mountain Geophysical Institute, Nalchik, Russia
INTRODUCTION
The northern slope of the Greater Caucasus
consists of 6 main ridges which lower from south to
north. In its Central part the range of altitudes var-
ies from 5.642 m in the Elbrus Mountain to 900 m
in the low mountains. A significant glaciation of 850
km
2
is typical in the case -study area of the Greater
Caucasus. Complex natural and climatic conditions
of the region predetermine high activities of de-
bris flow of pluvial, glacial, snow and its polygenic
glacial-pluvial and snow-pluvial origin (a
dzHiev
&
b
oGaCHenko
, 2003).
In period of 1951 to 2009 there has been recorded
1679 debris flow events of various genesis and mag-
nitude observed in 215 mountain river basins which
covered 5000 km
2
of the study territory. The events
featured magnitude heterogeneity as regards territory
and time. They included annual single and mass of
disastrous accidents with repeatability in 20-50 years
when up to 100 simultaneous debris flows were de-
scending through the inflows and channels of the main
rivers. Debris flows magnitude regulations caused by
glaciation process was defined (s
einova
, 2001).
As a result of the observation we obtained numer-
ical characteristics of meteopredictors promoting the
debris flow formation and the range of its maximum
and minimum (critical) values.
We applied a statistical method which allows
considering complex physical processes of debris
flow formation, virtually coded in the occurred de-
ABSTRACT
The paper presents a method of a short-term
forecast for meteorologically initiated debris flows
of different genesis. A diversity of an environment
of Greater Caucasus predetermines a wide spectrum
of geologic-geomorphologic processes and non-reli-
able meteopredictors which cause debris flows for-
mations. The water impulse which causes the debris
flows formation is connected with showers (pluvial
genesis) and also with glaciers thawing and snow
(glacial genesis and snow genesis). However debris
flows of polygenic meteo genesis, glacial-pluvial
and snow-pluvial are the most widespread. The last
is connected with fluctuation of the air humidity and
weather temperature that makes forecasting of the
hazardous events considerably difficult.
The proposed method of the debris flows fore-
casting is based upon numerical values resulted from
continuous long-term observation, since 1951 up to
2009. On the first stage we classified river basins by
prevailing debris flows genesis (pluvial, glacial-plu-
vial and etc.).The numerical mapping of the territo-
ries was made according to above mentioned basins
classification was made. The main meteo predictors
for each group of basins with homogeneity of debris
flows formation and their critical values were ob-
tained. The prediction of the dates of debris flows
events rely on a short-term daily temperature and
precipitation forecasting.
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O.A. kUMUkOVA, I.B. SEYNOVA, A.H. ADZHIEV & N.V. kONDRATJEVA
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
within the whole study area excepting some basins
with modern glaciation. When the frontal heavy
rains are durable, the air temperature in the place of
debris flow origin above 3000 m considerably drops,
causing solid precipitation and drastic reduction of
water flaw that prevent debris flow formation proc-
esses. For the last 50 years the mass pluvial debris
flows in nival-glacial zone were observed only in
1953 and 1967 with frontal rainfalls from 70 to 120
mm. In the middle mountains for the same period
such mass disastrous debris flow events were regis-
tered in 1953, 1958, 1967, 1975, 1977, 1986, 1996
and in 2002 (a
dzHiev
et alii, 2003, 2004) .
The rainfall-induced debris flows on the whole
study area occur during June-August.
GLACIAL-PLUVIAL AND GLACIAL DE-
BRIS FLOWS DISTRIBUTION
The area includes Vodorazdelny, Bokovoy and
Peredovoy, the highest part of Caucasus with aver-
age altitude of 4000 m and maximum above 5000
m. Disastrous debris flows of glacial-pluvial and
glacial genesis are induced by intensive degradation
of modern glaciation. As to the magnitude modern
glacial debris flows were not less disastrous than an-
cient debris flows the evidences of which remained
over the mountain valleys landscape. Debris flows
of polygenic glacial-pluvial genesis are more typical
for these areas. Mass debris flows were recorded in
1953, 1966, 1967, 1975, 1977, 1983 and 1995.
Debris flows glacial genesis was resulted from
inrush of glacial lakes and of moraine-glacial break-
down. The most destructive debris flows from the
middle of the 20
th
century were in 1960-1962, 2000,
bris flow events.
The main idea of the method is in priority of com-
bined influence of meteopredictors (temperature and
precipitation) on debris flow.
REGIONAL FORECAST OF DEBRIS
FLOWS OF DIFFERENT GENESIS
The principles of the suggested method proceed
from the previous studies devoted to the debris flows
of glacial-pluvial genesis forecast (a
ndReev
, s
eyno
-
va
, 1984, a
dzHiev
et alii, 2008).
A step-by-step differentiated approach has been
designed to forecast debris flows of different genesis.
It consists of the following items:
• classification and mapping of debris flow basins ac-
cording to the predominant genesis of debris flows;
• determination of the optimal values of meteo data
necessary and sufficient for debris flow process.
The interaction of climate factors and potential
sediment mass in debris flow origin basin is suggested
as the physical basis of the proposed methods.
BASINS CLASSIFICATION
We initially classified the basins by the predomi-
nant genesis of the debris flows formation using the
observed debris flow events in the case-study area
as the base. In accordance with such classification a
digital area mapping has been performed (s
eynova

et alii, 2001).
SNOW-PLUVIAL AND PLUVIAL DEBRIS
FLOWS DISTRIBUTION
The area includes several mountain ridges - Mel-
ovoy, Lesisty, Pastbichshny and Skalisty, rising to
the south-west from 500 m up to the escarp of Ska-
listy ridge with 3500 m - 4000 m altitude range. The
mass debris flows events were observed from April
till June initiated by heavy snow winters and com-
pleted by spring showers (s
eynova
, 1997).
A very dramatic activity of snow-pluvial and
snow debris flows proceeded since 1987 till 2002
due to the snowy winters and contrast climate fluc-
tuations. The contrasts of meteorological charac-
teristics in the mountain regions were intensified by
global warming. Consequently it caused disastrous
debris flows and floods after extremely snowy and
warm winters in 2001-2002.
Debris flows of pluvial genesis are widely spread
Fig. 1 - The map of the debris flows of rain, rainfall-snow
genesis distribution over kabardino-Balkarian
Republic (Central Caucasus)
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FORECAST OF DEBRIS FLOW HAZARD IN THE NORTHERN SIDE OF THE GREATER CAUCASUS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
915
above 0 until the debris flow.
Meteo predictors values of the items 1-4, deter-
mine directly the impulse to the debris flow initiation.
Meteo predictors of the items 5-6 display the level
of the preliminary readiness for potential debris flow
mass formation.
We found out that the magnitude of debris flow
for each individual event depends on the combina-
tion of the peak or exceeding it values of the above
meteorological characteristics. For every genetic type
of the debris flow we defined values of the critical pa-
rameters and their effect on the debris flow formation.
All 6 factors need to reach their peak values or
above simultaneously to form the debris flow stuff.
The allocated 6-dimensional area of the most prob-
able debris flow is the basis for forecast construction.
SHORT-TERM FORECAST STATISTICAL
FORMULA CONSIDERING THE PLU-
VIAL AND GLACIAL-PLUVIAL GENESIS
The range of critical meteoparameters ensures
the experts to determine probability of the debris flow
initiation. Forecast statistical formula is built on this
range of critical meteoparameters. It is possible to
present physical process of the debris flows formation
in formula modifying with parameters andvalid in
specified critical area.
This technique implies following steps:
1) we multiplied meteoparameters to give the
quasiphysical descript of accumulation and materi-
alization of the debris flows hazards considering tem-
perature and precipitation amount. Product of these
parameters presents one of the hydrothermal charac-
teristics widely used in climatology.
2006 and 2007.
The debris flow season lasts 2 months (July - Au-
gust).Figures 2, 3 present the map of glacial-pluvial
and glacial debris flows expansion over the territory
of Kabardino-Balkarian Republic (Central Caucasus)
METHOD OF SHORT-TERM FORECAST
OF DEBRIS FLOWS WITH DIFFERENT
GENESIS
The proper analysis and interpretation of the de-
bris flows events based on reliable observations define
the validity of forecast. The study of the debris flows
risk situations for each group of the basins has been
carried out on the basis of debris flows statistical data
of the events observed in high mountains of the Cen-
tral Caucasus in the period of 1951-2008.
We sampled the dates of debris flows events in-
duced by climatic conditions recorded with suffice ac-
curacy by meteo stations «Terskol» (2100 m a.s.l.) and
«Nalchik» (548 m a.s.l.). It included the dates of mass
debris flows (up to 100 events) over the whole Central
Caucasus in such years as 1967, 1977, 1983 et al., local
debris flows (10-20 events) in Baksan and the adjacent
valleys in 1966, 1975, 1980, 1995, as well as singular
debris flows took place nearby the meteo stations.
6 factors causing debris flows formation revealed:
1. daily precipitation, mm;
2. air temperature in a day with precipitation, °C;
3. six days precipitation amount prior to debris flow,
mm;
4. six days temperature amount prior to debris flow, °C;
5. precipitation amount (mm) from the day with t°
above 0 until the debris flow;
6. positive temperature amount from the day with t°
Fig. 2 - The distribution of glacial-pluvial debris flows
on the territory of kabardino-Balkarian Republic
(Central Caucasus)
Fig. 3 - The glacial debris flow expansion on the territory
of kabardino-Balkarian Republic
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O.A. kUMUkOVA, I.B. SEYNOVA, A.H. ADZHIEV & N.V. kONDRATJEVA
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
∑T
6
– summarized temperatures for the current 6 day
period, °C.
The prognosis for the debris flow forecast is made
when
FORECAST FOR RAINFALL DEBRIS
FLOWS
Rainfall debris flows are the most frequent within
the study area. Mass debris flows along the numerous
tributaries of interconnected net in big rivers basins
during frontal rainfalls 1% of provision (80-120 mm)
are the most disastrous in manifestation scales. From
1953 to 2003 rainfall debris flows were observed in
50% of all debris flows events including situations.
The analysis revealed that the rainfalls initiated
the debris flows events when the weather conditions
were as follows:
1. daily precipitation, (mm):
87,9 ≥ x ≥ x critical (x critical = 40);
2. air temperature on the day with precipitation,
(°C):
25,5 ≥ t ≥ t critical (t critical = 15);
3. precipitation amount for six days prior to the
debris flow, (mm):
69,0 ≥ ∑x
6
≥ ∑x
6
critical (∑x critical = 11);
4. daily temperature amount for six days prior to
the mudflow, (°C):
155,7 ≥ ∑t
6
≥ ∑t
6
critical (∑t
6
critical = 95);
5. precipitation (mm) amount from 0° prior to the
day of mudflow, (mm):
526, 7 ≥ ∑x ≥ ∑x critical (∑x critical = 200);
6. positive temperature amount from 0° prior to
the day of mudflow, (°C):
2311,2 ≥ ∑t ≥ ∑t critical (∑t critical = 902).
Dates of rainfall debris flows caused by meteo
factors as they were fixed in meteo station «Nalchik»
(548 m) and hydrologic stations «Zayukovo» (665
m), «Belaya Rechka» (672 m), «Kashhatau» (708 m),
«Nizhni Chegem»(880 m) are represented in table 1.
FORECAST FOR SNOW-RAINFALL DE-
BRIS FLOWS
Thus nature observations confirmed that a mass
snow-rainfall debris flow formation in the Greater Cau-
casus takes place after an extremely snowy winter season.
2) we summarized preceded the debris flows daily
meteoparameters to describe preparatory measures
For debris flows of glacial-pluvial genesis mostly
typical for high-mountain area it looks like:
where A and B are constant coefficients of the me-
teoparameters, obtained by means of statistical algo-
rithms.
To obtain coefficients we used:
1. critical characteristics of the meteofactors
which define boundary conditions for debris flow and
non-debris flow hazards. Their X
cr
, T
cr
, ∑T
6
, ∑t, ∑x
parameters were defined using reliable observation
data verified and confirmed statistically;
2. weighted characteristics of each meteofactor of
Px, Pt, or their combined effect on debris flow haz-
ards Pxt, P.. The factors weight was defined by fre-
quency of debris flows events relevant to total number
of daily observation in the range of optimal meteopa-
rameters characteristics used for forecast formula con-
struction
where Nr is number of daily observation of the debris
flows events, caused by achieving or exceeding the
critical points of each meteopredictor its;
Ni total number of daily observations in a range of
optimal meteoparameters.
To obtaine A and B coefficients we took weighted
characteristics of each meteofactor or their joint influ-
ence on the debris flows hazard in the range of criti-
cal parametres:
where Рxt, P∑T
6
is a weight of the joint factors;
X
cr.
, T
cr
. - critical value of meteofactors.
The total formula which describes additional sub-
stance that starts debris flow activity, has a sight of:
х – predicting amount of precipitation, mm;
t - predicting air temperature in a day of precipitation,
°C;
(1)
(2)
(3)
(4)
(5)
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FORECAST OF DEBRIS FLOW HAZARD IN THE NORTHERN SIDE OF THE GREATER CAUCASUS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
917
13,9 ≥ t ≥ t critical (t critical = 9);
3. precipitation amount within six days prior to
the debris flow, (mm):
59,6 ≥ ∑x
6
≥ ∑x
6
critical (∑x
6
critical =0);
4. daily temperature amount within six days prior
to the debris flow, (°C):
100 ≥ ∑t
6
≥ ∑t
6
critical (∑t
6
critical = 72);
5. precipitations amount (mm) from the day with
t° above 0° until the date of debris flow, (mm);
478,1 ≥ ∑x ≥ ∑x critical (∑x critical = 187);
6. positive temperatures amount from the day
with t° above 0° until the date of debris flow, (°C).
1455,1 ≥ ∑t ≥ ∑t critical (∑t critical = 670).
In table 2 the dates of debris flows of glacial -
rainfall genesis with specified meteo factors are repre-
sented according to dataset obtained by meteo station
«Terskol» (2100 m).
This prediction is based firstly on estimation of
preliminary humidification resulted from snow melt-
ing process in spring as the quantity of precipitation
during cold period are constantly observed with high
accuracy by the meteo stations and hydrologic sta-
tions. Forecast of rainfall - snow debris flows is car-
ried out according to the acknowledged methods of
hydrological forecast of spring floods
FORECAST FOR GLACIAL - RAINFALL DE-
BRIS FLOW
Calculations made show that the formation of de-
bris flow of glacial - rainfall genesis resulted from the
following weather conditions:
1. daily precipitation, (mm):
69,9 ≥ x ≥ x critical (x critical =22);
2. air temperature in a day with precipitation, (°C):
Tab. 1 - Dates of rainfall debris flows with causing them
meteo factors (according to data weather meteo
station «Terskol» , «Nalchik», hydrologic stations
«Zayukovo»,«Belaya Rechka», «Sovetskoe»
(kashhatau), «Nizhni Chegem») Categories: m –
mass debris flows (more than 20 simultaneously),
l - local debris flows (10-20 simultaneously),
s - single debris flows (up to 10 simultaneously);
∑t °C- sum of positive air temperatures from
the passage date through 0 to the date of debris
flows; ∑t °C- sum of positive air temperatures
for six days before the debris flow; t °C- avera-
ge temperature on the day of debris flows; ∑x
mm- sum of precipitations from the date positive
temperatures up to on the date of debris flows;
∑x6 mm- sum of precipitations for six days befo-
re debris flows; x mm – precipitation on the day
of debris flows
Tab. 2 -. Dates of glacial - rainfall debris flows according
to dataset of meteo station «Terskol» (2100m).
Categories: m – mass debris flows (more than
20 simultaneously), l - local debris flows (10-20
simultaneously), s - single debris flows (up to 10
simultaneously); ∑t °C - sum of positive air tem-
peratures from the passage date through 0 to the
date of debris flows; ∑t6 °C - sum of positive air
temperatures for six days before the debris flows;
t °C - average temperature on the day of debris
flow; ∑x mm - sum of precipitations from the date
of positive temperatures up to the date of debris
flow; ∑x6 mm - sum of precipitations for six days
before debris flows; x mm - precipitation on the
day of debris flow
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O.A. kUMUkOVA, I.B. SEYNOVA, A.H. ADZHIEV & N.V. kONDRATJEVA
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5th International Conference on Debris-Flow Hazards Mitigation: Mechanics, Prediction and Assessment Padua, Italy - 14-17 June 2011
FORECAST FOR GLACIAL DEBRIS FLOwS
The proportion of debris flows of glacial genesis
is only 10% of the total quantity of debris flows on the
territory of KBR for 50 year period.
Data analysis exhibited that debris flows of gla-
cial genesis occur in the following weather conditions
(Tab. 2):
1.
daily precipitation, (mm):
9,2 ≥ x ≥ x critical (x critical = 0);
2. daily air temperature with precipitation, (°C):
19,9 ≥ t ≥ t critical (t critical = 15);
3. precipitation amount six days prior to the de-
bris flow, (mm):
28,2 ≥ ∑x
6
≥ ∑x
6
critical (∑x
6
critical = 0);
4. daily temperature amount for six days prior to
the debris flow event, (°C):
107,1 ≥ ∑t
6
≥ ∑t
6
critical (∑t
6
critical = 94);
5. precipitation (mm) amount from t 0° till the
date of debris flow event, (mm):
553,5 ≥ ∑x ≥ ∑x critical (∑x critical = 260);
6. positive temperatures amount from 0° prior the
date of debris flow event, (°C):
1438,9 ≥ ∑t ≥ ∑t critical (∑t critical = 950).
It is determined, that for forecast the glacial debris
flows meteo predictors in the items 2 and 4, are of a
great significance.
CONCLUSION
The method of regional forecast is based on the
verified data analysis of the debris flows hazards mag-
nitude in space and time in the northern slope of the
Greater Caucuses from 1951 to 2010.The physic and
statistic analysis of the long term observations al-
lows forecast required numerical values obtaining for
meteopridictors and relative calculation algorithms
avoiding. Genesis and parameters of debris flows for
each event were determined by field data. Weather
conditions for all debris flows risk situations have
been studied using data of the meteo stations, water
power stations and observations in debris flow basins.
The complex analysis, detail study of the debris flows
mass formation in the study case territory and mete-
orological statistical dataset processing resulted:
a) classification and mapping of the debris flows
basins that are homogeneous by predominant debris
flows formation (glacial, glacial-pluvial, pluvial,
snow-pluvial types) and
b) numerical threshold values for the set of the
meteopredictors which cause debris flows descending
in the basins of the same genesis.
The debris flows forecasting is carried out by pre-
cipitation and air temperature prognosis considering
the precipitation rate occurred in the basins during the
warm period. The inspection on regional debris flows
forecast verification in the period of 2008-2010гг.
(60%) authorized including the designed method into
the Guidance document on debris flows forecast in the
system of the National hydrometeorology and envi-
ronment monitoring.
The authors consider the designed method as a
required transforming stage in further study of the de-
bris flows forecast in the basins with most risky situa-
tion for the population.
This work continues.
Tab. 3 - Dates of glacial debris flows with contributing
meteo factors according to the datasets of weather
station «Terskol» (2100 m). Categories: m – mass
debris flows (more than 20 simultaneously), l - lo-
cal debris flows (10-20 simultaneously), s - single
debris flows (up to simultaneously); ∑t6 °C - sum
of positive air temperatures from the passage date
through 0° to the date of debris flows; ∑t °C - sum
of positive air temperatures for six days before the
debris flow; t °C - average temperature on the day
of debris flow; ∑x mm- sum of precipitation from
the date positive temperatures up to the date of
debris flows; ∑x6 mm - sum of precipitation for
six days before debris flows; x mm - precipitation
on the day of debris flow
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FORECAST OF DEBRIS FLOW HAZARD IN THE NORTHERN SIDE OF THE GREATER CAUCASUS
Italian Journal of Engineering Geology and Environment - Book www.ijege.uniroma1.it © 2011 Casa Editrice Università La Sapienza
919
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