Mudflow hazard in the foothill and mountainous regions of Uzbekistan

The article presents the results of research work on the study of mudflows in the territory of the Republic of Uzbekistan and transboundary territories. The relevance of studies of mudflow phenomena is determined by the intensive development of economic and recreational development of mountain and foothill territories, which in the conditions of the Republic of Uzbekistan are subject to mudflow processes that cause material damage to the objects of the national economy and are often accompanied by human casualties. About a thousand active mudflow channels have been counted in the study area, of which over 270 descend into the Fergana Valley. The most mudflow-prone regions in Uzbekistan are: Namangan - 19% of all registered mudflows, Fergana - 16%, Surkhandarya - 13%, Tashkent - 12%, Kashkadarya - 11% and Samarkand - 9%. In general, the Fergana Valley accounts for 41% of the total number of all registered mudflows. A sharp increase in mudflow activity is observed in April and May. During these months, respectively, 25% and 35% of mudflows descended. As a rule, these are mudflows that came down as a result of a large amount of precipitation. The most mudflow-prone regions in Uzbekistan are: Namangan - 19% of all registered mudflows, Fergana - 16%, Surkhandarya - 13%, Tashkent - 12%, Kashkadarya - 11% and Samarkand - 9%. In general, the Fergana Valley accounts for 41% of the total number of all registered mudflows.


Introduction
When people talk about mudflows, as a rule, the imagination of its phenomenon is very contradictory. In Central Asia, according to the concept of local residents, it is customary to call a mudflow of short-term high intensity precipitation (showers), as a result of the fallout of which a mass of small streams is formed, from the confluence of which powerful flows of enormous destructive force often arise. This last, which has already been transformed in the modern concept, is called mudflow.
Mudflows are mountain streams saturated with solid material that are formed in some basins mainly from rainfall [1].
Mudflowis a natural disaster causing enormous damage to the national economy of many regions of our republic. Mudflows cause human casualties and death of livestock, destroy industrial facilities and residential buildings, hydraulic structures, bridges, roads, communication lines and power transmission lines, bring in agricultural fields and the irrigation network, destroy orchards, vineyards and crops.
The study of the engineering-geological conditions for the formation of mudflows, the state and properties of mudflow-forming rocks in the system of the Ministry of Geology of Uzbekistan began in 1964 by engineering-geological teams under the direct methodological guidance of VSEGINGEO and GIDROINGEO.
To understand the essence and regularities of the formation of mudflow centers, their relationship with the main types of mudflow formation mechanism, the nature of the development and transformation of mudflows, specialized engineering-geological and hydrogeological studies of individual regions of the republic and mountainous regions surrounding it were carried out.
A systematic study of mudflows in Uzbekistan was first organized in the southwestern spurs of the Gissar ridge in 1928. Mountain-mudflow parties were created (Fergana, Namangan, Kashkadarya, Surkhandarya). The mudflow regime of watercourses in the area was investigated by employees of hydrometeorological stations. In 1966-1968 V. A. Kudyshkin and V. A. Bondar carried out a regional study of mudflows. In 1972, Yu. N. Ivanov and VL Babko identified mudflow centers and flooding zones of the Kashkadarya region. At the end of the last century, NIGMI carried out a large number of works on the study of mudflow formation, the study of synoptic processes affecting mudflow, developments were carried out in the field of forecasting mudflow hazard [3][4][5][6][7][8][9][10]. All these developments formed the basis of the modern stage of research in the field of mudflow formation and the spread of mudflows in the territory of the Republic of Uzbekistan.
Studies carried out by international experts provide evidence of a close relationship between climate change and an increase in the frequency and intensity of dangerous hydrometeorological phenomena leading to climatic disasters, which justifies the need for a comprehensive study of mudflow phenomena in the main mudflow-prone areas located in the basins of mountain and foothill rivers. In recent decades, research in this area has been Priority attention is given, since the creation of early warning systems contributes to improving environmental safety, protecting the economy, population and vital human interests from the possible negative impact of dangerous hydrometeorological phenomena and is of particular relevance [11][12][13][14][15][16][17][18].

Initial data and research methods
When conducting research on mudflow phenomena, the main methods of obtaining information are expeditionary observations, route geomorphological mapping, as well as operational information coming from the Uzhydromet network. The materials of the Scientific Research Hydrometeorological Institute and the data of hydrometeorological observations of the Center of the Hydrometeorological Service of the Republic of Uzbekistan were used as the main initial information for this study. These materials are supplemented with data from expeditionary observations and field experimental materials used after their processing by conventional methods, including methods of mathematical statistics -correlation and multivariate analysis, an objective method of aligning and normalizing correlations. In the process of performing the work, the methods of cartographic research, comparative geographical, the method of geographical generalization and analogy were widely used.

Main part
Mudflows are widespread in the mountainous regions of Central Asia and South-East Kazakhstan, representing a characteristic feature of the regime of many rivers and temporary streams (Fig. 1). Information about them has been available since 1874. Mudflows were most developed in the Fergana and Issyk-Kul basins, southwestern regions of Uzbekistan, in the Tashkent oasis, the Nuratau mountains, the Zarafshan river basin, the northern and southwestern parts of Tajikistan, the mountains of Turkmenistan, the northern ridges of the Tien Shan, the Dzhungar Alatau, Saur -Tarbagatai and the Kazakhstan part of Altai. About a thousand active mudflow channels have been counted on this territory, of which more than 270 descend into the Fergana Valley. It is necessary to take into account the fact that many mountain territories within Kazakhstan and Central Asia are still far from insufficiently studied in terms of mudflows [15][16][17].
Mudflow basins, within the above territory, have catchment areas from a fraction of km2 to 100 km2 and more. Most of them (76%) are up to 100 km2 (Fig. 2).  The main mudflow areas on the territory of the Republic of Uzbekistan are currently the following: 1 Fergana Valley with its mountainous framing (the southeastern slopes of the Kuramin and Chatkal ridges, the southern and southwestern Atoynak, the Isfanjailo, Baubashat ranges, the southwestern slopes of the Fergana, northern Alay and eastern parts of Turkestan, the Mogoltau ridge and the Utoynak). The Fergana Valley is a zone of the most active mudflow and, in general, can be considered as one of the most significant regions in Central Asia in terms of the development of mudflow processes. Almost all slopes (channels) descending to it are more or less mudflow hazardous, but among them there are areas of maximum development of mudflows, which include, first of all, the southeastern slopes 3 Mountains of Tashkent oasis (Karzhantau ridges , Ugamsky, Pskemsky, Sandalashsky and southwestern slopes of the Chatkal ridge). The Chirchik river basin is most muddy, especially in the middle and lower reaches, as well as the Chirchik-Akhangaran (Angren) interfluve, where the selenos are Sukoksay, Bashkyzylsay, Parkentsay, Zarkentsay, Altynbelsay, Aksakatasai, Karamazarsay, Karankulsay. The Akhangaran basin is less mudflow active, however, there are frequent cases of catastrophic mudflows. The main mudflow streams are located on the right bank within the low mountains (southern slopes of the Chatkal ridge). These are Yakkarcha, Toganbashisay, Dukantsay, Karabausay, Akchasay, Shavazsay. A number of mudflow channels descend from the northern slopes of the Kuraminsky ridge (Naugarzan, Nishbash, Shaugazsay, Almalyksay, Karakiyasay). The Tashkent group also includes mudflow streams of the Keles River basin and located on the southwestern slopes of the Kuraminsky ridge (Sordobsay, Utkansai). [21,22]  5 Valley of the Zarafshan River (southern slopes of the western part of the Turkestan ridge, northern and southwestern -Zarafshan, northern -Gissar with its western spurs). The main mudflow streams are located in the middle and lower parts of the basin. The most muddy-ridden is the northern slope of the Zarafshan ridge (middle reaches of the Zarafshan), where the basins of the Fandarya, Kshtut, Magiandarya and a number of sais (Madm, Vashan, Zavron, Chinorsay, Saursay, Zebonsai) are distinguished. A number of mudflow channels exist in the Kshtut-Fandarya interfluve (left bank). On the right bank of the selenose forest there are Obikrut, Duoba and several nameless sais. In the upper part of the basin, the southern slopes of the Zarafshan Range, where there are a number of mudflow streams, are prone to mudflow. In the lower part (northern and southwestern slopes of the Zarafshan ridge), Urgut, Tersaksay, Ayakchidarya, Gavkhonasay, Kalkamassay, Kuruksay, Taragaysay, Lyangar, Tolokolsay, Kiyakulisay, Sazagansay, Aksaiysh, as well as the Saai Uplands belong to the seleniferous ones. The Zerafshan basin sometimes also includes selenium-bearing watercourses in the Sanzar and Zaaminsu basins, as well as those located in this interfluve (Achisay, Karamazarsay, Pshagarsay, Kuzhapishkent, and a number of others). In the Sanzar and Zaaminsu basins, mudflows occur on the northern slopes of the Turkestan ridge and, less often, on the western ones.
Mudflows are mainly formed in the basins of the Surkhandarya river in March -June with a maximum in April and the Kashkadarya river in April -May with a maximum in April due to rainfall, intense snow melting and heavy rains.
Also in April, the maximum mudflow activity occurs in the Samarkand and Tashkent regions. In May, there is a peak in Namangan, Fergana, Andijan, Jizzakh, Syrdarya and Navoi regions (Table 1). In general, in Uzbekistan, the maximum number of mudflows occurs in May (Fig. 3).
In connection with the enormous potential danger of mudflows, it becomes necessary to assess the possible risk to people. Risk is understood as the possibility of undesirable consequences from any action or undesirable course of events. There are two categories of risk. One category characterizes the risk to human life and is defined as the number of victims per unit of time. Another category is related to material damage and is measured by cost indicators per unit of time.  Mudflow events in Uzbekistan are accounted on the basis of "information about past mudflows", where the mudflow is recorded simply as a spontaneous phenomenon, without taking into account the flow rate and flow rate, and is characterized by two gradations: OY -a dangerous phenomenon that causes material damage, and OHL -spontaneous a hydrometeorological phenomenon accompanied by human casualties (Table 2). I categorywith mudflow discharge over 500 m 3 /s; II categorywith discharge from 100 till 500 m 3 /s; III categorywith discharge less than 100 m 3 /s; IV categorywith discharge of 10 m 3 /s. 96 settlements of our republic are located in the territories under the II, III and IV categories of mudflow hazard. In Kashkadarya region, 3 settlements are located in the zone of the 1st category of mudflow hazard with a possible discharge more than 500 m3/s.

Conclusion
Analysis of materials on mudflows and mudflow activity showed that mudflows of all types are observed in Uzbekistan, but mudflows caused by heavy rainfall dominate (85% of the total number of registered mudflows).
Mudflows of this type occur during intense and prolonged precipitation. Mudflow activity in Uzbekistan manifests itself mainly in the period from March to August. In some years, the first mudflows are possible in February. A sharp increase in mudflow activity is observed in April and May. During these months, respectively, 25% and 35% of mudflows descended.
As a rule, these are mudflows that came down as a result of a large amount of precipitation. The most mudflow-prone regions in Uzbekistan are Namangan -19% of all registered mudflows, Fergana -16%, Surkhandarya -13%, Tashkent -12%, Kashkadarya -11% and Samarkand -9%. In general, the Fergana Valley accounts for 41% of the total number of all registered mudflows.