CC BY
3https://doi.org/10.55764/2957-9856/2022-2-28-34.10
УДК 627.141.1
E. Tsereteli1, N. Bolashvili2, G. Gaprindashvili3, M. Gaprindashvili4
doctor of Sciences in Geography, main scientist (Tbilisi State University, Vakhushti Bagrationi Institute of Geography, National Environment Agency, Tbilisi, Georgia) 2Doctor of Geography, main scientist (Tbilisi State University, Vakhushti Bagrationi Institute of Geography,
Tbilisi, Georgia)
3Doctor of Geography, scientist (Tbilisi State University, Vakhushti Bagrationi Institute of Geography,
National Environmental Agency of Georgia, Tbilisi, Georgia) 4PhD student (Department of Geology, National Environmental Agency of Georgia, Tbilisi, Georgia)
MUDFLOW PROCESSES IN GEORGIA
Abstract. Natural calamities become more topical in the beginning of XXI century, as the pressure of them on human environment becomes much heavier. Background of global climate change processes immeasurably increases the risk of uncontrollable natural catastrophes. Among the multi-spectral geological processes in Georgia the most impressive phenomena are landslides and debris/mudflows, washing out of marine coasts and river banks within the limits of settlements. According to special research data, the landslide, mudflow, and river bank erosion out reactivation processes are growing exponentially from year to year.
Keywords: Climate change, Debris flow, Geology, Hazard, Mudflow.
Introduction. Georgia is one of the mountainous countries, where the multi-spectral natural catastrophes are distinguished by development scale, recurrence frequency, and negative consequences for population and economy. Besides that, the territory of the country is located within the limits of 7-9 point intensity earthquake risk area. The earthquakes are directly connected with stimulation of landslide-gravitational and debris/mudflow phenomena. Major part of Georgian population, agricultural lands, roads, oil and gas pipe-lines, hydro-technical and irrigation facilities, electric transmitting lines, and mountainous tourism facilities periodically endure the attacks of natural phenomena. The risk area is rapidly increasing, that can be proved by the data of "SakGeologia" (Geology service of Georgia) collected in areas of risk zone on caused damage in different years (figure 1).
5
1970 1977 1981 1987-1988 1991-1992 1997 2009 2020
Figure 1 - Areas of the risk zone of natural geological processes and areas damaged in different years in Georgia
According to data of UN experts, more than a half of damage caused by elemental processes to the world population and economy, including casualties, is related to Debris/mudflows, Landslides and Floods. These processes are fully connected with climatic factors. Despite the continuous efforts of human
to overcome these dangerous phenomena, the risk of them remains the same, even at the background of modern sciences and technologies. There are not still invented any reliable ways for solving this problem.
These hardly predictable phenomena represent one of the most serious problems for Georgia. 40% of territory of the country is under the threat. While floods are mostly threatened lowland population, debris/mudflow risk must be taken into account almost for all geo-morphological zones, starting with foothills, and ending by high mountain-nival zone. Among 5 000 rivers transformable into mudflows in the Caucasus, about 3 000 are within the borders of Georgia. It should be taken into account as well, that about 60% of population live in the small river basins, most of which are also debris/mudflow transformable. Hundreds of settlements are located within the area of mudflow activity (in Tbilisi it is recorded more than 50 debris/mudflow gorges), as well as highways, railways, trans-Caucasian gas pipe-line and Baku-Tbilisi-Ceyhan oil pipeline, irrigation facilities and agricultural lands.
Caucasian region is under big interest of researchers for already more than 150 years because of complex natural conditions of mudflow development processes and because of significant damage caused to population and engineering facilities [1]. For instance, the mudflow developed in Telavi (1977) ravine damaged the infrastructure of town Telavi, calculated as 30 million dollars. Mudflow developed in the same year in upper stream of river Tskhenistskali caused damage of about 100 million dollars to local population and economic facilities. Mudflows developed in mountainous Ajara in 1982-84 and 1989-91 caused damage of 300 million USD.
The discussion of the results. Not only high intensity mudflows are dangerous for mountain population and their engineering-economic facilities, but also the low and medium intensity. These types of mudflows developing in extremely sensitive geological conditions of Tsiv-Gomboro, Saguramo-Ialno, Kartli, Iagluji, Kvernaki ridges, and surrounding hills of Tbilisi, are characterized by intensive development of mudflows and high recurrence (downpours of more than 30-40 mm/per 24 hours always cause mudflow transformations). They are highly dangerous for population and engineering-economic facilities (figures 2, 3).
Figure 2 - Debrisflow in Rikoti Pass Figure 3 - Debrisflow in Tbilisi (Svanidze str), June 2015
(Khashuri Municipality), June, 2011 (Photo George Gaprindashvili)
(Photo George Gaprindashvili)
Large scale development of diverse mudflow processes (caused by downpours or developed in result of clogging of ravines by landslide processes) in Caucasus in general and particularly within the territory of Georgia is conditioned by extremely 'sensitive' geological environment and specific climatic features. Mudflows provoking by downpours (65-85%) dominate on others, also considering particular geological conditions, caused by landslides and rock avalanches (10-30%) [2].
Intensity of the development of mudflows in Georgia (as regards time and space) is increasing from North-West towards South-East. This is conditioned by increasing of climate continentality, by increasing of aridity and decreasing of humidity coefficient, by narrowing of mountain forest belt and gradual decreasing of plant cover, and, which is more significant, by wide distribution of geologically unstable rocks in regard to erosive and denudation processes.
According to statistical analysis data the same amount of mudflow forming downpours cause different effects in different areas according to geological environment all over the world mountain countries. The same amount and duration of precipitations can cause either high waters, or typical mudflows. For instance, the minimal amount of daily precipitations for Carpathians is 30 mm, for Crimea Mountains -from 25 mm to 70-100 mm, Altay and Jungarian mountain areas - from 30-40 mm to 70-90 mm. In Tien Shan and Pamir-Alay mountain system the daily precipitations over 60-100 mm take place once in 100 years, while in the rest regions of Middle Asia 50-80 mm of precipitations take place once in 20 years in average [3].
Distribution of downpours in space and time in Caucasus is not still well investigated. According to I. Salukvadze [1]. the percentage of downpours in the whole number of precipitations in South Caucasus is highly changeable, depending on the distance from sea and the relief. In particular, for Poti it is over 80%, for Samtredia - 23%, for Tsipa - 12%, for mountain Sabue and Khashuri it is approximately 5%, for Tbilisi - 49%, and for Telavi - 44%. Though the daily distribution of precipitations in space is quite complicated, it can be said that, taking into consideration specific sensitivity of a given geological environment, the lower threshold of a mudflow forming sum precipitations is 30-40 mm per day. At the same time, the shorter is period, during which this amount is performed, the higher is probability of intensive mudflows, and in other words, period and intensity are in invert correlation. Cases of duration of precipitations, from 4-6 days to 32-48 days during warm season are described in Black Sea coastal zone and mountain regions of Georgia. Almost the same mean amounts, 30-50 mm of downpours are described in eastern part of Caucasus. Difference is noticed only in their recurrence frequency. Mudflow transformations can be observed in almost all geologically 'sensitive' river catchment basins in case of daily downpours of 50-80 mm. Together with increasing of intensity of precipitations, geographical scale of mudflows is also increasing. It is proved by investigations that in case of daily precipitations of over 80120 mm, catastrophic mudflows develop in all climatic-geological environments. For instance, downpours of frontal character (over 120 mm per day) at Caucasus scale caused in June, 14, 1944 and August 17, 1953 catastrophic mudflows at regional level. Precipitations in amount of 170-185 mm fallen in one day (10-11 August of 1977 and 19 July of 1983) on the both slopes of Caucasus caused catastrophic mudflows in basins of rivers Tskhenistskali, Alazani, and Baksani and their tributaries. It should be noted that if until 70s of XX century the recurrence mean frequency of mudflow forming precipitations (over 80-120 mm) for the Caucasus was described as once per 20 years, and once in 40 years for the Lesser Caucasus, significant increasing of the recurrence frequency is observed during the last period. For instance, according to data of Lagodekhi Meteorological Station, the maximal amount of such type of precipitations (over 150 mm) was registered 3 times in 1983, 2 times in 1986, and once in 1988. Each time catastrophic mudflows developed in Kakheti river basins.
It should be noted that at the edge of XXI century the activation periods of mudflows (like of other exo-geological processes) and their geographical scale are being considerably increased. Data given in table and figure 4 prove the above-mentioned observation. This must be connected first of all to the in-creased frequency of mudflow forming precipitations, which in its turn is provoked by global climate change [4, 5].
On May 17, 2014, a catastrophic debris/mudflow event occurred at the confluence of the Tergi River and the Devdoraki-Amali River in the Dariali Gorge. On May 17, a rock-avalanche came down from Mt. Mkinvartsveri (figure 5), bringing along five million cubic meters of rock, which was covered by ice and snow. The rock mass fell down on the Devdoraki glacier, deformed it and went on to the Devdoraki River. From the confluence with the Amali River, the flow transported the rock debris and mud downstream to the lower reaches. At the confluence of the Amali and Tergi rivers, the flow created a huge debris cone, approx. 2 mln m3, that totally blocked the Dariali Gorge (figure 6) and took the lives of eight people. On August 20, 2014, heavy rainfall in Devdoraki valley triggered the movement of the huge debris mass that had accumulated there on May 17, 2014, turning it into a mudflow and killing two people working at a hydroelectric power plant construction site near Tergi River. The events of May 17 and August 20 caused major material damage to the country as a whole, disrupting the Georgian Military Highway, the North-South Gas Pipeline, cutting a high-voltage power transmission line, damaging vehicles, blocking the access to a border defense facility and customs checkpoint, the Residence of the Georgian Patriarchate, and causing huge everyday problems to people working there. The main causes of the disaster were the geological structure of the area, local tectonics and morphology, as well as the negative impacts of climate change [4, 6].
Extreme activation years of mudflow processes in Georgia
River basins Years Mean recurrence frequency, year
Chorokhi- Ajaristskali basin 1921, 1932, 1948, 1953, 1961, 1970, 1972, 1977, 1982, 1984, 1986, 1988, 1987-89, 1991, 1996, 1998, 1999, 2001, 2003, 2004, 2005, 2008, 2014, 2018, 2020 3.6
Enguri basin 1954, 1955, 1959, 1960, 1964, 1966, 1968, 1970, 1972, 1975, 1976, 1977, 1981, 1982, 1987, 1988, 1989, 1992, 1997, 2002, 2003, 2004, 2005, 2019, 2020 2.2
Tskhenisrskali upper basin 1915, 1921, 1932, 1934, 1939, 1940, 1953, 1961, 1963, 1966, 1970, 1973, 1975, 1976, 1977, 1982,1984, 1987, 1988, 1992, 1997, 2003, 2004, 2005, 2008, 2010, 2021 3,6
Rioni upper basin 1921, 1932, 1939, 1940, 1953, 1961, 1963, 1966, 1970, 1973, 1975, 1976, 1977, 1982, 1984, 1987, 1988, 1992, 1997, 2003, 2004, 2005, 2008, 2010, 2020 3.6
Tergi upper basin 1776, 1778, 1785, 1808, 1817, 1827, 1832,1842, 1897, 1909, 1910, 1929, 1935, 1937,1944, 1953, 1955, 1956, 1957, 1959, 1966, 1967, 1968, 1970, 1981, 1982, 1996, 2002, 2003, 2004, 2007, 2014 7,45
Aragvi basin 1897, 1903, 1920, 1926, 1931, 1940, 1952, 1953, 1954, 1960, 1963, 1964, 1967, 1969, 1971, 1972, 1973, 1975, 1977, 1978, 1979, 1980, 1981, 1982, 1983, 1986, 1987, 1988, 1992, 1994, 1996, 1997, 1998, 2000, 2002, 2004, 2005, 2006, 2007, 2008, 2009, 2014, 2017, 2020 7,2
Kakhetian Caucasus 1899, 1903, 1906, 1922, 1934, 1947, 1949, 1951, 1952, 1956, 1957, 1958, 1961, 1962, 1963, 1967, 1970, 1973, 1975, 1976, 1977, 1981, 1983, 1984, 1988, 1989, 1990, 1991, 1995, 1998, 1999, 2002, 2003, 2005, 2010, 2018, 2020 3.02
Figure 4 - New / re-activated Debris/mudflows in Georgia, 2011-2018, by region [5]
Figure 5 - Rock-avalanche (Debrisflow source area) (Photo M. Gaprindashvili)
Figure 6 - Blocked Tergi river and created reservoir (Photo M. Gaprindashvili)
On June 13-14 2015, heavy rainfalls caused a sharp rise in water levels in the Vere River and its tributaries, and triggered large-scale landslides and debris/mudflows, which resulted in the disruption of adjacent highways. Landslides turned into muddy streams, the river waters full with the debris mass flooded some districts of the Georgian capital (figure 7), Tbilisi, and washed away and/or inundated houses and infrastructure at the lower reaches of the Vere valley, killing 23 people. The disaster almost destroyed the Tbilisi Zoo, many animals were killed and others were found outside the zoo. Together with other triggers (geology, morphology, tectonics, hydrogeology), the natural disaster on the Vere river was caused by the fast increasing of the river level resulting from heavy rainfalls (about 149 mm) associated with climate change, and primarily by a landslide with an area of 32 hectares and a volume of 1 mln cubic m that had formed between the villages of Tskneti and Akhaldaba (figure 8), a significant part of which clogged into the Vere riverbed. At the same time, more than 100 landslides were activated in the valley on June 13-14. Long-term geological observations and analyses show that debris/mudflows occur in relevant geological conditions in case of 40-50 mm rainfall per day. The stronger the rainfall, the more extreme mudflows would occur [4, 7].
Figure 7 - Debris.mudflow in Tbilisi Figure 8 - Akhaldaba "big" Landslide
(Photo G. Gaprindashvili) (Photo G. Gaprindashvili)
Conclusion. The territory of Georgia, is divided into 9 conditional areas (figure 9) [8] by damage caused by debris/mudflow processes, and according to the hazard risk which is based on syncretic synergism of the elements, which are part of geological environment system, characterized by extremely complex multifactorial features and debris flow processes stimulating factors:
Debrisflows
Figure 9 - Debris/mudflow hazard zones in Georgia
1. The area with very high damage probability and with high risk of recurrence (Ks-0.8-0.9), includes: Low and middles sized mountains constructed with Molasse sediments of Intermountain Belt of Eastern Georgia, Upper parts of riv. Rioni, Tskhenistkali, Enguri, Tergi, Aragvi basins. Transformation of debris/mudflows takes place almost every year (daily rainfall 30-50 mm and more). Often it is repeated several times in a year.
2. The area with high damage probability and hazard risk (Ks-0.6-0.8), includes: Area constructed with flysch rows and Mesozoic shale of north and south slopes of central and eastern segments of the Caucasus, highland of Adjara of Lesser Caucasus. Debrisflows recurrence period once in 2-3 years. Wide range of released materials volume - 0.1-0.2 mln.m3.
3. The area with significant probability of damage by debris flow transforming rivers and hazard risk (Ks-0.5-0.6) includes Trialeti and Meskheti ranges, middle and upper part of the river Kodori (western Caucasus) and river Bzipi basins. Debris flows recurrence period once in 3-5 years. The volume of material released by debrisflows from thousands of cubic meters to amounts 0.5-1.0 mln. m3.
4. The area with moderate risk of debrisflow hazards (Ks-0.3-0.5), includes middle part of the rivers Rioni, Tskhenistskali, Enguri and Kodori basins, headwaters of river Kvirila basin, low and middles sized mountain zone of Aphazeti Caucasus, the basin of river Algeti, Trialeti range on the territory of Tbilisi city, lowlands of Adjara. Debrisflows recurrence period once in 3-10 years.
5. The area with limited debris flow hazard risk (ks-0.1-0.3), includes: lowland zone of raised horst of the Dzirula, Khrami, and Loqi, Foothills of Guria and Imereti, debrisflows in the basins of rivers Psou, Sandripshi, and Zhoekvara take place once in 3-7 years, the volume of released material amounts 5-10 000 m3.
6. The area with low probability of damage caused by debris flow processes and hazard risk (Ks- 0.01-0.1), includes areas constructed by carbonate rocks of low and middle sized mountains of Racha, Askhi, Khvamli, Arabika, and rivers Bzipi and Kodori, foothills of Guria and Adjara.
7. The area with very low probability of damage caused by debris flow processes and hazard risk (Ks-<0.01), includes: Iori Plateau and part of the downstream of river Mtkvari;
8. The area weak probability of damage caused by debrisflow processes and hazard risk includes Akhalkalaki plateau and volcanogenic highland of Javakheti.
9. The area, where is no danger by debris flow hazard risk, includes Kolkheti lowland and Black Sea coast, plains of Eastern Georgia, Kartli and Alazani.
REFERENCES
[1] Salukvadze I. Storm precipitation in mountainous countries on the example of Transcaucasia. Tbilisi: TSU, 1988. 267 p.
[2] Tsereteli E.D. Natural-catastrophic effects and the problem of sustainable development of Georgia and border areas. Tbilisi, 2003. 109 p.
[3] Tatashidze Z., Tsereteli E., Bondirev I., Tsereteli N. Relevance of climatic anomalies in the development of exogeo-dynamic processes // Collected works of the institute of geography. Tbilisi, 2006. № 1(80). P. 107-120.
[4] Gaprindashvili G. Geological Hazards in Georgia // Fourth National Communication of Georgia under the UNFCCC. Tbilisi, 2021. P. 258-290.
[6] Bolashvili N., Tsereteli E., Kutsnashvili O., Gaprindashvili G., Kurtsikidze O. Climate as an integral synthesizer in development-reactivation processes of landslide and diagnostic criterion of its evaluation // Engineering geology for Society and Territory, Springer. 2015. Vol. 2. P. 1781-1786.
[6] Gaprindashvili G., Gaprindashvili M. Catastrophic Debrisflow in Dariali (Georgia) in the Year 2014 // Natural Science. 2015. 7. P. 379-389. doi 10.4236/ns.2015.77041
[7] Gaprindashvili G., Gaprindashvili M., Tsereteli E. Natural Disaster in Tbilisi City (Riv. Vere Basin) in the Year 2015 // International Journal of Geosciences. 2016. 7. P. 1074-1087. doi 10.4236/ijg.2016.79082
[8] Tsereteli E., etc. Mudflows, map in National Atlas of Georgia. Stuttgart, 2018. P. 41.
Э. Церетели1, Н. Болашвили2, Г. Гаприндашвили3, М. Гаприндашвили4
1Г.г.д., бас гылыми кызметкер (Тбилиси мемлекетпк университет^ Вахушти Багратиони атындагы география институты, ¥лттьщ коршаган ортаны коргау агентпп, Тбилиси, Грузия) 2Г.г.д., жетекш гылыми кызметкер (Тбилиси мемлекетпк университет^ Вахушти Багратиони атындагы география институты, Тбилиси, Грузия) 3Г.г.д., гылыми кызметкер (Тбилиси мемлекетпк университет^ Вахушти Багратиони атындагы география институты, Грузияныц коршаган ортаны коргау ^лттык агентпп, Тбилиси, Грузия) 4PhD докторант (Грузия ¥лттык коршаган ортаны коргау агентппнщ геология департамент^
Тбилиси, Грузия)
ГРУЗИЯДАГЫ СЕЛ ПРОЦЕСТЕР1
Аннотация. ХХ1 гасырдыц басында табиги апаттар езекп бола тусуде, олардыц адамныц тiршiлiк ету ортасына кысымы айтарлыктай артып келедi. Климаттын жаhандык езгеруi процестерi аясында бакылан-байтын табиги апаттардын каупi елшеусiз есуде. Грузиядагы кеп спектрлi геологиялык процестердiн iшiнде ен эсерлi к¥былыстар кешк1н мен сел, тещз жагалаулары мен елдi мекендердегi езен жагалауларынын эро-зиясы болып табылады. Арнайы зерттеулер бойынша кешк1н мен сел процестерiнiн, жагалау эрозиясынын каркыны жылдан-жылга артып келедг
Непзп сездер: климаттын езгеруi, сел, геология, кауш, лайлы сел.
Э. Церетели1, Н. Болашвили2, Г. Гаприндашвили3, М. Гаприндашвили4
1Д.г.н., главный научный сотрудник (Тбилисский государственный университет, Институт географии
им. Вахушти Багратиони, Национальное агентство по охране окружающей среды, Тбилиси, Грузия) 2Д.г.н., ведущий научный сотрудник (Тбилисский государственный университет, Институт географии им. Вахушти Багратиони, Тбилиси, Грузия) 3Д.г.н., научный сотрудник (Тбилисский государственный университет, Институт географии им. Вахушти Багратиони, Национальное агентство окружающей среды Грузии, Тбилиси, Грузия) 4PhD докторант (Отдел геологии, Национальное агентство по окружающей среде Грузии, Тбилиси, Грузия)
СЕЛЕВЫЕ ПРОЦЕССЫ В ГРУЗИИ
Аннотация. В начале XXI века стихийные бедствия становятся все более актуальными, их давление на среду обитания человека значительно возрастает. На фоне происходящих процессов глобального изменения климата неизмеримо возрастает риск возникновения неконтролируемых природных катастроф. Среди многоспектральных геологических процессов в Грузии наиболее впечатляющими являются оползни и селевые потоки, размывы морских побережий и берегов рек в пределах населенных пунктов. По данным специальных исследований, из года в год происходит стремительный рост оползневых и селевых процессов, размывов берегов.
Ключевые слова: изменение климата, селевой поток, геология, опасность, грязевой поток.
