What is a mudflow, and how to escape from this phenomenon? Mudflow (mudflow).

Mudflow (mudflow)- a stormy mud or mud-stone flow that suddenly appears in the beds of mountain rivers.

The immediate causes of mudflows are heavy rainfalls, washing out of reservoirs, intensive melting of snow and ice, as well as earthquakes and volcanic eruptions. Anthropogenic factors also contribute to the occurrence: deforestation and degradation of soil cover on mountain slopes, rock explosions during road construction, stripping operations in quarries, improper organization of dumps and increased air pollution, which has a detrimental effect on soil and vegetation cover.

The likelihood of mudflows occurring depends on the composition and structure of rocks, their ability to weather, the level of anthropogenic impact on the area and the degree of its environmental degradation.

Under weathering refers to the process of mechanical destruction and chemical change of rocks and minerals. The intensity and speed of weathering are characterized by natural processes ( precipitation, wind, air temperature fluctuations, etc.).

A mudflow occurs when a number of conditions coincide in time: a certain, sufficiently large supply of rock destruction products, a significant volume of water to carry debris from the slopes of the mudflow basin, and a steep drainage. A mudflow basin includes a mountainous area covering the slopes that feed the mudflow with rock destruction products, its sources, all its channels, the catchment area, as well as the area of ​​its impact.

The processes of occurrence and development of mudflows depend on such characteristics of mudflow basins as the height of the sources, mudflow activity, as well as the geological structure and erosion of rocks. Based on the height of mudflows, the basins are divided into high-mountain (2.5 km), mid-mountain (1.0-2.5 km) and low-mountain (up to 1 km). The basins are also characterized by the volume of debris flow. The higher the source, the greater the volume of debris flow from 1 km 2 of the basin surface.

Based on mudflow activity, pools are divided into three groups:

1) highly seleniferous, characterized by intensive formation and the presence of loose clastic material; their mudflow capacity is equal to 15-35 thousand m 3 of outflow from 1 km 2 of active area per mudflow;

2) medium-seleniferous, distinguished by intense processes of weathering and erosion; their mudflow capacity is significantly lower and ranges from 5-15 thousand m 3 ;

3) weakly seleniferous, have a less intense weathering process and an undeveloped hydrographic network with some deformation of the channel and slopes; their mudflow capacity is up to 5 thousand m 3 .

The process of formation and development of mudflows goes through 3 stages:

1. Accumulation of loose material in the channels of mudflow basins due to weathering of rocks and mountain erosion.

2. Movement of loose rock materials along mountain beds from elevated areas to lower areas.

3. Concentration of mudflows in mountain valleys.

Mudflow movement is a continuous stream of mud, stones and water. Mudflows can transport individual rock fragments weighing 100-200 tons or more. The leading front of the mudflow wave forms the “head” of the mudflow, the height of which can reach 25 m.

The duration of movement of mudflows is most often 1-3 hours, less often - 8 hours or more. The structural composition is determined by the content of solid material in the flow volume, which accounts for up to 75%. The density of the mudflow mass (volumetric weight) ranges from 1.2-2 t/m 3 . It depends on the structural composition.

The frequency of mudflows in different mudflow-prone areas varies. In areas of rain and snow feeding, they can be repeated several times during the year, but more often - once every 2-4 years. Powerful - observed once every 10-12 years or less.

Mudflows are divided according to the composition of the transported material, the nature of movement and power (volume).

According to their composition, mud flows are distinguished - a mixture of fine earth water and a small amount of small stones; mud-stone - a mixture of water, fine earth, gravel, pebbles and small stones; water-stone - a mixture of water with large stones.

According to the nature of movement, there are connected and disconnected mudflows. The former consist of a mixture of water, clay, sand and are a single plastic substance. Such a mudflow, as a rule, does not follow bends, but straightens it. The second is a mixture of water, gravel, pebbles and stones. It rushes along the bends of the riverbed at high speed, subjecting it to destruction.

By power (volume), mudflows are divided into catastrophic, powerful, medium and low power. Catastrophic ones are characterized by the removal of more than 1 million m3 of material. They are registered on our planet, as a rule, once every 30-50 years. Powerful ones carry material with a volume of 100 thousand m 3 or more. These rarely occur.

In mudflows of low power, the removal of material is insignificant and amounts to less than 10 thousand m 3. They occur annually, sometimes several times a year.

Collapses

Landslides (mountain landslide) - separation and catastrophic fall of large masses of rocks, their overturning, crushing and rolling down steep and steep slopes.

Landslides of natural origin are observed in the mountains, on the shores of seas and oceans, and on the cliffs of river valleys. This is the result of a weakening of the cohesion of rocks under the influence of weathering, erosion, dissolution and the action of gravity. Their formation is facilitated by the geological structure of the area, the presence of cracks and zones of crushing rocks on the slopes.

Most often (up to 80%) modern collapses are associated with the anthropogenic factor. They arise mainly when work is carried out incorrectly during construction and mining.

These emergency situations are characterized by the power of the landslide process (the volume of falling rock masses) and the scale of manifestation (the area involved in the process). According to the power of the landslide process, they are divided into large (rock detachment of 10 million m 3), medium (up to 10 million m 3) and small (rock detachment of less than 10 million m 3). “The scale of manifestation of landslides allows us to define them as huge (100-200 hectares), medium (50-100 hectares), small (5-50 hectares) and small (less than 50 hectares). In addition, landslides can be characterized by the type of collapse, which is determined the steepness of the slope of the landslide masses.

Protection of the population in case of threat and during landslides, mudflows and landslides. The population living in landslide-, mudflow- and landslide-hazardous zones should know the sources, possible directions and main characteristics of these dangerous phenomena. Based on the forecast data, people are provided with information in advance about identified landslide, mudflow, landslide sources and possible zones of their action, about the periods of passage of mudflows, as well as about the procedure for submitting signals about the threat of these emergency situations.

If there is a threat of a landslide, mudflow or landslide, and if there is time, advance evacuation of the population, farm animals and property to safe places is organized. Before evacuating a house or apartment, everything must be done to weaken the damaging factors of a natural disaster, prevent the occurrence of secondary factors and facilitate subsequent possible excavations and restoration. To do this, all things necessary for the family must be moved from the yard or balcony into the house; the most valuable property that cannot be taken with you must be protected from moisture and dirt. Close doors, windows, ventilation and other openings tightly. Turn off electricity, gas and water supply. Highly flammable and toxic substances removed from the house and, if possible, buried in remote pits or separate cellars. In all other respects, citizens act in accordance with the procedure established when organizing the evacuation.

When there is no advance warning of danger and residents are warned about the threat only immediately before the onset of a natural disaster or notice its approach themselves, each of them, without worrying about property, urgently and independently selects a safe place. At the same time, relatives, neighbors, and all people encountered along the way should be warned about the emergency situation.

Natural safe ways for immediate evacuation are the slopes of mountains and hills that are not subject to landslide processes or those between which there is a mudflow-hazardous direction. When climbing to safe slopes, valleys, gorges and recesses should not be used, as side channels of the main mudflow may form in them. During evacuation, assistance should be provided to the sick, elderly, disabled, and weak children.

It happens that people, residential buildings, and other structures find themselves on the surface of a moving landslide area. Then, having left the premises, you need to move upward and, acting according to the situation, beware when braking the landslide, boulders, stones, fragments of structures, and an earthen rampart appearing from the rear part of it. Moreover, a landslide can also take over an overthrust of immovable rocks, and if its speed is high, a strong shock is possible at the moment it stops. All this represents great danger for people in the landslide.

After the end of a landslide, mudflow or landslide, people who had previously hastily left the disaster zone and waited out it in a nearby safe place (after they are convinced that there is no repeat threat) should return to the emergency zone to search for victims and provide assistance to them.

Consequences of landslides, mudflows and landslides. Landslides, mudflows, landslides cause great damage to the national economy, natural environment, often result in human casualties.

The main damaging factors of disasters are impacts from moving rock masses, as well as the collapse or flooding of previously free space. As a result, residential buildings and other structures collapse, and entire settlements, national economic facilities, agricultural and forest lands are buried under layers of rock. River beds and overpasses are blocked, people and animals die, and the landscape changes.

Landslides, mudflows, landslides are the most dangerous enemies of agriculture. Mudflows lead to flooding and obstruction of agricultural crops with debris over areas of hundreds and even thousands of hectares. Arable lands located below landslide areas often become swampy. All of the above leads not only to crop loss, but also simply to the removal of land from agricultural use.

The scale of the consequences of landslides, mudflows, landslides is determined by:

The size of the population caught in the landslide zone;

The number of dead, wounded and homeless;

The number of settlements caught in the natural disaster zone and national economic facilities, medical, health and socio-cultural institutions that were destroyed and damaged;

The area of ​​flooding or obstruction of agricultural land;

The number of dead farm animals.

The secondary consequences of these natural disasters are emergency situations associated with the destruction of technologically hazardous objects, as well as the interruption of economic and vacation activities.

On the territory of the Russian Federation, landslides, mudflows and landslides occur in the mountainous regions of the North Caucasus, the Urals, Eastern Siberia, Primorye, on the island of Sakhalin, Kuril Islands, Kola Peninsula, as well as along the banks of large rivers.

Landslides often lead to large-scale catastrophic consequences. Thus, in 1982, a mudflow 6 m long and up to 200 m wide hit the villages of Shivel and Arenda in the Chita region. Houses, road bridges, 28 estates were destroyed, 500 hectares of cropland were washed away and covered, people and farm animals died. Economic damage amounted to about 250 thousand rubles.

Usoi collapse (1911) on the river. Murghab in the Pamirs with a volume of 2.2 billion m3 formed a natural dam 8500 m high, and Sarez Lake 56 km long and up to 500 m deep appeared.

A landslide in Italy (1963) with a volume of 240 million m3 covered 5 cities, killing 3 thousand people.

In Colombia, following the eruption of the Rusch volcano in 1985, a giant mudflow occurred, which, after traveling 40 km, overwhelmed the city of Armero, where 22 thousand people died. and 4.5 thousand residential and administrative buildings were destroyed.

In 1989, as a result of landslides in Checheno-Ingushetia in 82 settlements, 2,518 houses, 44 schools, 4 kindergartens, 60 healthcare, cultural and public service facilities were seriously damaged.

Measures to prevent landslides, mudflows, landslides and reduce damage. Preventive measures to protect against landslides, mudflows, landslides are divided into passive and active .

The first group includes measures of an organizational, economic and security-restrictive nature: prohibition of the construction of industrial enterprises, residential buildings, iron and highways without reliable structures to protect them from mudflows; limit in necessary cases movement railway trains in areas adjacent to landslide or landslide areas; prohibition of the construction of ponds, reservoirs, and water-consuming facilities on slopes without taking measures to completely prevent water leakage into the ground, etc.

The second group includes active measures, the implementation of which is associated with the construction of engineering and hydraulic structures.

To prevent landslide processes, retaining walls, counter-banquets, pile rows, etc. are used. The most effective anti-landslide structures are counter-banquets. They are located at the base of a potential landslide and, by creating a stop, prevent the soil from moving.

The group of active measures to reduce the risk of landslides also includes fairly simple measures that do not require significant resources for their implementation, especially in terms of the consumption of building materials. To reduce the stressed state of slopes, cutting off earth masses in the upper part and laying them at the foot is often used. The interception of groundwater above a possible landslide is carried out by installing a drainage system. Protection of coasts and seas from landslides is achieved by importing beach material.

Hydraulic structures are used to protect against mudflows. Based on the nature of their impact on mudflows, they are divided into:

Selereregulating;

Seedling;

Mud-retaining;

Seletransforming.

Among the mudflow-controlling hydraulic structures, in turn, there are mudflow-control structures (chutes, seleduks, mudflow diversions), mudflow-control structures (dams, retaining walls), mudflow-removing structures (dams, thresholds, drops) and mudflow-control structures (half-dams, spurs, booms). All of them are built in front of dams, belts and retaining walls.

Mudflow dividing hydraulic structures are cable mudflow cutters, mudflow barriers and slot dams. They are designed to retain large pieces of debris and allow small pieces of debris flow to pass through.

Mudflow-retaining hydraulic structures include dams and pits.

Mudflow transforming structures (reservoirs) are used to transform a mudflow into a flood by replenishing it with water from reservoirs. Along with preventive and protective measures, an important role in preventing the occurrence of these natural disasters and in reducing damage from them is played by monitoring landslide, mudflow and landslide-hazardous areas, harbingers of these phenomena, and predicting the occurrence of landslides, mudflows and landslides.

As a result of excessive concentration of industry in certain regions, the complication technological processes, the use of a significant number of explosion, fire, radiation and chemically hazardous substances, wear and tear of equipment, there is an increase in the number of accidents and disasters, the number of human casualties is increasing, and material damage from man-made emergencies is increasing. The socio-economic consequences of natural emergencies are also great.

All this forces us to increase the efficiency and reliability of managing processes of both prevention and elimination of consequences.

We need a lot of systematic work, which is expected to be completed over several years. For this purpose, a special program has been developed and approved,

consisting of subroutines that are executed in two stages.

The first - 1993-1995. and the second - 1995-1997. As a result of its implementation, an automated information and control system for warnings and actions in emergency situations (AIUS RSChS) appeared, which will interface with local and regional links of similar systems.

This will allow advance warning of the population, authorities, enterprises, organizations, institutions and educational establishments about the occurrence of emergency situations and, therefore, respond adequately to the prevailing conditions. Ultimately, reduce losses in people and material assets to the maximum extent possible.

MINISTRY OF EDUCATION AND SCIENCE OF THE RUSSIAN FEDERATION

FEDERAL AGENCY FOR EDUCATION

State educational institution

higher professional education

"ROSTOV STATE CIVIL UNIVERSITY"

Department of Engineering Geology, Foundations and Foundations

Essay

on the topic: "Mudflows"

Completed:

student of group PZ-119

Maliko Elena

Checked:

Prof. Peredelsky L.V.

Rostov-on-Don 2013

Chapter 1. General information

1.1 The concept of mudflow

1.2 Genetic classification of mudflow events

Chapter 2. Conditions for the formation and development of mudflows

Chapter 3. Mudflow disasters

Chapter 4. Protection of territory and structures from mudflows

4.1 Preventive measures

4.2 Engineering protection

Bibliography

Chapter 1. General information

1.1 The concept of mudflow

Mudflows (from Arabic, "sayl" - a stormy stream) are sudden short-term mountain streams consisting of a mixture of solid material and water. Mudflows occur as a result of heavy and prolonged rainfall, during periods of rapid melting of snow and glaciers, as well as when dams, dams, etc. break.

Mudflows are a formidable natural phenomenon, often of a catastrophic nature. A huge mass of water rushes down the gorges, washing away and capturing eluvium and colluvium along the way. As a result, the water flow is enriched with solid material and turns into a mud-stone flow.

In the area of ​​mudflows, there is a constant threat of destruction of bridges, dams, pipelines, buildings and structures in populated areas, blockage of perennial plantings, crops, etc. with mud-stone masses. Areas prone to mudflows are called mudflow-dangerous.

The huge mudflow on July 8, 1921, which suddenly burst out of a mountain gorge on the river, is well known. Malaya Almaatinka near Almaty and collapsed on the city. More than 200 buildings were ripped off their foundations and destroyed, killing about 400 people. The mudflow carried 1.5 million tons of mud-stone material onto the city area.

Mudflows are common in all mountainous regions of the world, except Antarctica. In Russia, 25% of its entire territory is classified as mudflow-prone areas (North Caucasus - Kabardino-Balkaria, Dagestan, North Ossetia; Kola Peninsula, Sayan Mountains, Baikal region, Kamchatka, etc.). The classic areas where mudflows occur in the CIS are the mountainous regions of Central Asia, Transcaucasia and Kazakhstan.

The characteristic features of mudflows, in addition to suddenness and short duration of action, are the pulsating nature of the movement (due to the resulting congestion), very high speed of movement (up to 10 m/s), high erosive and impact-destructive ability due to the presence of solid material. The volume of individual blocks entrained by a mudflow can reach more than 60 m3, the mass is about 150 tons, and the energy of mudflow pressure on an obstacle is from 5 to 12 tons per 1 m2.

The great destructive impact of mudflows is due to high movement speeds and the presence of rock fragments in them. Along their path, mudflows often create deep channels that are usually dry or contain small streams. Mudflow material is deposited in the foothill plains. Useful areas are buried under a layer of mud, sand and stones.

If we take these properties as guiding ones, mudflows or mudflow-like phenomena, in addition to mudflows themselves, should include flows in which the solid component is represented by snow and ice, as well as specific flows formed in the subaquatic environment. Based on the systematization of the main types of mudflows and mudflows, taking into account the manifestation environment, material composition and parameters. Four groups of flows are identified.

Actually mudflows - mud and water-stone flows, mudflows.

Paracelaceae, including snow-water and ice-water flows. The solid component in them is represented almost exclusively by snow and ice. They differ from the actual mudflows in their significantly lower density and weak erosion-accumulation activity.

. Ultra mudflows: gigantic in scale (they are in the nature of geological disasters), unique in terms of formation conditions.

. Quasi-debris flows - mudflow-like phenomena on the bottom of seas and oceans, known as turbidity currents. Their scale exceeds the scale of ultra-mud flows on land, and the movement continues on the almost flat surface of the abyssal plains. Includes two types of flows - high and low density.

Figure 1. Rain mudflow.

.2 Genetic classification of mudflow events

Classes	The main factor of formation	Main features of distribution and mode		Cause and mechanism of origin
I. Mudflows of zonal manifestation	climatic (variability of hydrometeorological elements)	distribution is widespread and zonal in nature; mudflows are systematic; the escape paths are relatively constant	1) rain	showers and prolonged rains, causing erosion of slopes and riverbeds, landslides
			2) snowy	intense snow melting, causing a shift of waterlogged snow or soil masses, breakthrough of snow dams
			3) glacial	intensive melting of snow and ice, causing a breakthrough of accumulations of melted glacial waters, collapse of moraines and ice
P. Regional mudflows	geological (active endogenous processes)	distribution is limited to areas of greatest tectonic activity; Mudflows are episodic; the exit paths are not constant	4) volcanogenic	explosive volcanic eruptions, accompanied by the descent of crater lakes, rapid snowmelt, etc.
			5) seismic - genic	earthquakes with a magnitude of 8 and above, causing the disruption of soil masses from the slopes
			6) limno - gene	destruction of natural lake dams, accompanied by erosion of the riverbed by a breakthrough wave
Sh. Anthropogenic mudflows	Economic activity (violation of the stability of mountain landscapes)	They develop in areas of greatest economic pressure on the mountain landscape; the frequency of disappearance is increased compared to the natural background, less often it is episodic in nature; the emergence of new mudflow basins is typical	7) anthropogenic (technogenic)	storage of mine dumps on steep slopes and their subsequent erosion; construction of low-quality earthen dams and their destruction, etc.
			8) natural-anthropogenic	deforestation and degradation of meadow vegetation due to irrational exploitation of the territory, unleashing erosion and mudflow processes

2.1 Rain mudflow is one of the genetic types of mudflows, formed as a result of heavy rains and prolonged rains. The mechanism of generation of d.s. in most cases it is of the erosion type:

2.2 Snow mudflow is one of the genetic types of mudflows, the occurrence of which is caused by the processes of accumulation and melting of snow cover and snowfields.

There are two types of s. With. - snow flows and snowfalls. The first serves as the main type of mudflow phenomena in the middle mountains of the subarctic zone. Snow mudflows are common both in the Subarctic and in the alpine and subnival zones of the highlands of the temperate zone. Most common the mechanism of their generation - breakthrough of temporary dams formed by channel and avalanche snowfields in narrowing valleys. Such breakthroughs usually form water-stone streams or mudflows; most typical for the Subarctic. The second, more rare mechanism for the origin of snow mudflows is associated with the accumulation (mainly through avalanche demolition and weathering) on ​​the benches of the longitudinal profile of denudation incisions and channels of loose clastic mass, which, when waterlogged, is capable of self-flowing; thus forming mud-stone streams. This type of mudflow occurs in the highlands of the temperate zone. The main impulse ensuring the descent from. pp., is served by intense snowmelt, sometimes with the participation of rain. The period of descent from. With. in the subarctic zone it occurs in spring, in the highlands of the temperate zone - in summer. By volume mudflows With. s belong to the medium group.

2.3 Glacial mudflow is one of the genetic types of mudflows, the formation of which is associated with a violation of the stability of glacial-moraine complexes, and the liquid component is formed mainly due to melted glacial waters.

The emergence of l. With. is caused by the breakthrough of glacier-dammed lakes and intraglacial reservoirs, as well as the sliding or disruption of moraine and ice masses.

By composition mudflow mass l. With. can be water-stone, mud-stone, water-ice.

L.S. the most powerful mudflows in the highlands; their distribution zones border the areas of modern mountain glaciation. Activation l. With. characteristic of the stage of degradation of glaciation, especially for its initial stages.

Syn: glacial debris flow.

2.4 Volcanogenic mudflow - one of the genetic types mudflow events, the formation of which is caused by a volcanic eruption of a predominantly explosive type. Mechanism of nucleation V. With. associated with the descent of crater lakes, with intense melting of snow and ice, etc.

V. s. - the most powerful among all types of land mudflows (see. Ultra mudflows). The length of their path reaches 300 km, the volume of displaced debris masses is 500 million/m³, the thickness of sediments is 20 m. With. differ in the inconsistency of the descent path; participate in the formation of volcanogenic-proluvial volcanoes.V. With. - one of the main sources of danger during volcanic eruptions.

2.5 Seismogenic mudflow is one of the genetic types of mudflows, which is caused by an earthquake of magnitude 8 or higher. The origin of the village With. associated with the removal of soil masses from slopes, sometimes with the release of water from mountain lakes. Slides caused by an earthquake can be transformed into a mudflow directly; landslides and landslides create temporary dams, the breach of which serves as an impetus for the occurrence of mudflows.S. With. - rare type mudflow events, characteristic of areas with high seismic activity.

2.6 Limnogenic mudflow is one of the genetic types of mudflows, the occurrence of which is associated with the erosion of natural lake dams and the release of part or all of the water of a mountain lake. Outburst-dangerous lakes are of the dammed (dammed) type; they are formed as a result of damming the river by landslides, landslides, lava flows, ancient glacial moraines, and alluvial cones of lateral tributaries. Similar types of lakes exist for hundreds to first thousand years, and their breakthrough is prepared by long processes of evolution of the lake dam, including suffusion, etc.

L.S. - a rare type of mudflows, characteristic of seismically active highlands.

K l. With. It also does not include some of the rain and snow types of mudflows, the formation of which involves breakthroughs of small ephemeral dammed lakes in river beds; their existence is limited to hours, less often to days.

2.7 Anthropogenic mudflow is one of the genetic types of mudflows, the formation of which is directly related to the consequences of economic activities that radically change environmental conditions.

The centers of origin of a. With. most often serve dumps and reservoirs; the former provide the solid component of mudflows, the latter - the liquid component during a breakthrough. Repeatability A. With. increased compared to the frequency of mudflows of natural origin, less often of an episodic nature; The distribution is local and includes lowland areas.

2.8 Natural-anthropogenic mudflow is one of the genetic types of mudflows, the conditions for the formation of which are associated with a situation in which the consequences of economic activity serve as an impetus for changing the course of natural processes and subsequent development mudflow phenomena. As a rule, the reason for the formation of p. - a. With. deforestation, degradation of meadow vegetation in the mountains due to overgrazing, plowing of steep slopes; this leads to increased erosion, increased sediment runoff, and then the development mudflow processes. P-a. With. characterized by high repeatability. and low density (often dominated mudflows), abundance slope mudflow basins. Distribution of p. - a. With. is regional in nature, covering both territories that survived the industrial revolution and areas of ancient civilizations.

Chapter 2. Conditions for the formation and development of mudflows

The main conditions for the development of mudflows are:

) large area of ​​the mountain river drainage basin;

) accumulation of a sufficient amount of loose weathering products in the drainage area and in the beds of watercourses;

) prolonged heavy rains after a dry period or rapid snowmelt; less often - a breakthrough of water from natural or artificial reservoirs (moraine lakes, reservoirs, etc.).

Human engineering and economic activity, and primarily the denudation of mountain slopes through predatory deforestation and destruction of bushes, can have a significant impact on the formation of mudflows.

During engineering-geological surveys for construction in mudflow-prone areas, it is customary to distinguish (Fig. 26.6):

The zone of formation (feeding) of mudflows is the upper part of the mudflow basin, within which the accumulation of loose material occurs;

Transit (transfer) zone - ‘the middle part of the basin, where the movement of the mudflow occurs and its replenishment with solid material;

The deposition zone is the lower part of the basin, in which the velocity of the mud flow sharply decreases, and the transported material is deposited in the form of alluvial cones.

At the initial stages of engineering-geological research, it is necessary to establish the degree of danger of the territory planned for construction development. It is estimated by the volume of material removed after the passage of one mudflow (G.I. Klio-rina, V.A. Osin et al., 1984). The first degree of danger includes territories where the volumes of removal exceed 1 million m3, the second - with volumes of removal from 0.5 to 1 million m3, and the third - less than 0.5 million m3.

Engineering-geological surveys in mudflow-prone areas are carried out in conjunction with engineering-hydrometeorological surveys in agreement with the territorial service of the Ministry of Natural Resources of Russia, which monitors (observes) mudflows in this area.

A mudflow, like any flood, is associated primarily with the intense runoff of surface (rain and melt) waters, which erode, wash away and transport loose material accumulating in the drainage basin of a mountain river, temporary watercourse or some part of them. There are known examples of mixed feeding of mudflows by rain and melt water. Finally, mudflows also occur during outbursts of glacial (for example, on the Malaya Almaatinka River in 1973) and non-glacial lakes and artificial reservoirs.

As is known, the water balance of rivers

Q = x- (z + u).

Since mudflow phenomena are short-term and develop in mountains, i.e. rough terrain, evaporation G and infiltration And within drainage basins compared to the amount of incoming rain and melt water X negligible. Consequently, the flow rate Q should be determined by the amount of rain and melt water entering the drainage basin, the speed and simultaneity of their reaching the main watercourse on which the mudflow is formed.

The speed and simultaneity of water reaching the main watercourse are determined by the size and shape of the drainage basin and the slopes of the surface of its relief. The amount of expenditure, other things being equal, will depend on the size of the basin and the intensity of precipitation.

In conditions of an asymmetrical pool (Fig. IV-3, b) surface runoff will be regulated at the site P the flood will increase gradually, it may be longer, but its magnitude (other things being equal) is less than in a symmetrical basin.

Consequently, the climatic and often microclimatic conditions of water supply of mountain rivers, which determine the intensity of runoff surface waters hydrological conditions are the first and most important factor in the formation of mudflows.

The great living destructive force of mudflows occurs under the influence of gravitational forces, which cause the movement of huge water-stone and mud-stone masses at high speeds. The action of these forces characterizes the energy of the relief and is proportional to the excess of the drainage basin over the erosion base and the magnitude of the surface slopes of its relief.

Consequently, geomorphological conditions are the second indispensable factor in the formation of mudflows.

Observations show that the valley of the most mudslide-prone rivers can be divided into three parts.

The upper part (upper reaches of the river), where the valley is expanded and is shaped like a semicircle with steep (from 30-40 to 50-60°), steep slopes in sections, covered with screes, stone placers, with traces of landslides, various landslide movements. The slopes are often dissected by deep gullies, ravines and ravines, along which rain and melt water flow from all sides, forming the main stream. This is the main part of the river’s drainage basin, where mudflows mainly form. The area of ​​this part of the catchment area can vary from several square kilometers to many tens of square kilometers.

The middle (transit) part of the valley, which is a canyon, gorge or a narrow part of the valley with steep and high slopes. The slope of the river bed remains high - up to 25-30°. Even during low-water periods, the river here often occupies the entire bottom of the valley, flowing in one stream or several among piles of blocks, boulders and smaller debris. During a flood, the stream is partially saturated with debris due to the erosion of the river bed, valley slopes, and accumulations at their base.

The lower (mouth) part of the valley, gradually turning into a foothill plain or intermontane depression. This part of the valley is mainly an area of ​​removal and accumulation of proluvial material. Here the slopes of the longitudinal profile of the valley sharply level out and the living force of the flow weakens.

This structure of valleys is not typical for all mudflow-prone mountain rivers and temporary streams, although it is often observed.

There are examples when the middle (transit) part has a small extent or is almost absent. In such cases, the entire valley participates in the formation of a mudflow flood.

The main drainage area of ​​a mountain river valley can be located at different absolute and relative altitudes.

For high-mountain basins located above the upper limit of forest distribution, i.e. at elevations approximately above 2500 m, there is a wide distribution of products of physical (frost) weathering, various colluvial accumulations in the form of stone placers, ridges, as well as glacial (mainly moraine) deposits. In such basins, in the formation of mudflows, along with rainwater, a significant role is played by meltwater from glaciers and snowfields, as well as water outbursts from glacial lakes. Mudflows that form in such basins are very dangerous; they are characterized by large volumes, flow rates and enormous destructive power.

In mid-mountain basins, usually located at elevations from 1000-1200 to 2000-2500 m, the filling of floods with solid debris occurs due to the erosion and washing away of various formations - accumulations of landslides, screes, landslides, colluvium, eluvium, alluvium, less often moraine and fluvio-glacial . The formation of mudflows in such basins occurs mainly due to torrential rains. Mudflows here are also quite dangerous.

In low-mountain basins located at elevations below 1000-1200 m, the formation of mudflows also occurs mainly due to rain (storm) water and a wide variety of types of loose formations - colluvial, deluvial, eluvial and alluvial. These sediments contain more clayey rocks and clayey impurities, since chemical weathering processes play a significant role here. Therefore, mud-stone mudflows often form in such basins.

The composition of the mudflow mass is influenced not only by the dominant type of weathering within the basin, but also by the composition of the rocks composing the basin. If the structure of the mountain ranges of a particular drainage basin involves clayey, carbonate-clayey, sandy-clayey rocks, the loose material formed during their destruction will also be clayey to one degree or another. Accordingly, the mudflow will be mud-stone or mud.

The volume of debris flows and flow rates within low-mountain basins is usually less than in others.

The most important condition determining the formation of mudflow floods is the accumulation of loose clastic and clayey-clastic material within the drainage basin or in some part of it accessible to washout and erosion by surface river, as well as rain and melt water. This material can be of very diverse origin: colluvial, colluvial, eluvial, alluvial, glacial and fluvio-glacial. In terms of its composition, it can also be very heterogeneous and consist of blocks, fragments, boulders, pebbles, crushed stone, sand, gruss and gravel, sandy loam and loam of different sizes.

The composition of loose material within the drainage basin is also influenced by other geological processes that take part in its formation, such as landslides, screes, landslides, glacial and water-glacial activity, etc. These processes create hotspots in certain areas of the drainage basin loose material washed away during floods.

Important to note that since a mudflow occurs suddenly and develops at high speed (“avalanche”), the loose material carried away and eroded by it during the transfer process does not have time to undergo any noticeable differentiation and sorting, although it continues to be destroyed, crushed, processed, etc. .d. Therefore, mudflows, both water-stone and mud-stone, are characterized by a large heterogeneity of the composition of solid material, and this should be considered one of their characteristic features. In the zone of removal and accumulation of loose material, where flow rates sharply decrease, the differentiation and sorting of the material brought by it is noticeable and significant.

It was noted above that depending on the altitudinal position of the drainage basin and, consequently, its physical and geographical conditions, the type and composition of loose material changes. In high-mountain basins, conditions are favorable for the accumulation of loose clastic material. Along with this, moraine and fluvio-glacial deposits are common here. Within the mid- and low-mountain basins, along with the accumulation of loose clastic material, the development on the slopes of various clayey deluvial, eluvial, landslide and other formations is characteristic.

Among other geological conditions influencing the formation of mudflows, it is necessary to pay attention to the tectonics of the region; ancient tectonic movements usually cause tectonic disturbance and fragmentation of rocks, zones of disturbance, brecciation, mylonitization, etc. All this further facilitates their erosion and the replenishment of floods with solid material . Therefore, zones and areas of large fragmentation of rocks are also sources of accumulation of loose material for mudflows. The newest and modern tectonic movements, firstly, usually maintain the contrast of the relief, its energy and thereby constantly influence the living force of floods and, secondly, cause earthquakes and, as a consequence, the massive formation of landslides, screes, landslides, avalanches, the role of which in accumulation of loose material within the catchment area has already been noted.

Despite the fact that loose formations accumulating within drainage basins play a large role in the formation of mudflows, their properties, as well as the properties of the mudflow mass, have been studied by almost no one anywhere, although knowledge of these properties is of undoubted interest. There are only fairly numerous data on their granulometric composition. Among the properties characterizing the mudflow mass, there is data on its density, which is determined indirectly - by the method of calculating the possible maximum saturation of mudflows with solid material. The properties of individual facies of proluvial deposits have been studied in detail, but they do not at all characterize the loose formations of catchment areas and mudflow mass.

Thus, the main conditions on which the formation of mudflows depends are the following.

Climatic and microclimatic conditions of the region, which are associated with uneven distribution of precipitation, the formation of showers, accumulation of snow and glaciers and their rapid melting during indefinite summer periods.

Geomorphological conditions that determine the size and shape of drainage basins, their altitude position, slopes of relief surfaces and the structure of mountain river valleys and temporary watercourses.

Geological conditions that determine the accumulation of loose material in drainage basins or in some parts thereof, the development of various geological processes (weathering, gravitational, etc.) involved in the formation of this material, as well as ancient, recent and modern tectonic movements.

Human activities causing disruption of natural balances in watersheds.

The cause of mudflow processes, their driving force, are floods - intense surface runoff as a result of rainfall, rapid melting of snow and glaciers in the mountains, and sometimes water breakthroughs from natural and artificial reservoirs.

Chapter 3. Mudflow disasters

There are many known mudflow disasters. For example, on the night of August 17-18, 1891 in Tyrol, a mudflow wave from a gorge in the Austrian Alps reached a height of 18 m, as a result of which a vast area was covered in a short time with a thick layer of mud-stone material. One of the largest cities on the US Pacific Coast, Los Angeles, repeatedly suffered from mudflows (January 25, 1914, January 1, 1934 and March 1, 1938). The mudflow of 1938 carried out a mud-stone mass from the mountains with a volume of more than 11 million m8 at an average flow rate of 2000 m8/sec and caused colossal losses, killing more than 200 people.

July 1921, after a heavy rainfall in the Trans-Ili Alatau mountains, a mud-stone mudflow struck the city of Alma-Ata, passing in waves every 30-60 seconds. He brought more than 3.5 to the city. million m* of solid material. At the Medeo site, its consumption amounted to 1-1.5 million m3.

Over the past decades, numerous mudflow events have been observed in the mountainous regions of Central Asia, the Caucasus, Crimea, the Carpathians, and Transbaikalia.

Among foreign examples, the most famous are the mudflow disasters of 1970 in Peru, as a result of which more than 60 thousand people died and 800 thousand were left homeless. Several cities were destroyed.

Figure 3 Passport for the Medeu mudflow control dam

Figure 4 Cross and longitudinal sections of the dam. Medeu

On July 1973, at 17:55 local time, as a result of the breakthrough of moraine lakes in the upper reaches of the basin, a mudflow was formed, which rushed along the Mynzhilka trough valley into the bed of Malaya Almaatinka.

The formed mud-stone flow filled the reservoir in front of the Medeo dam in 2 hours and brought 4 million m3 of mudflow deposits. The maximum flow rate of the mudflow reached 2-3 thousand m*/sec, the average - 500 m*/sec.

On the evening of July 16, two more mudflow waves passed along the bed of Malaya Almaatinka. On July 18, about 0 m remained to the lower point of the dam crest. This, as well as the possibility of repeated mudflows, created a threat of overflowing the dam and required urgent measures. The government commission recommended the following as priority measures:

a) pumping out water and suspended matter accumulated in front of the dam;

b) filling the sinus with rock mass in the left abutment of the dam, left for the construction of a mudflow;

c) organizing regular observations of dams and glacial lakes;

d) preventing the filling of glacial lakes;

e) timely discharge of water from them in the event of a tendency for such filling.

The first two recommendations made it possible to quickly obtain additional mass storage capacity of up to 4 million m9, i.e. the same volume as the mudflow that occurred on July 15, 1973. Thus, the mudflow protection dam in the Medeo tract made it possible to completely accumulate the masses of the mudflow, reliably protect the city of Alma-Ata located below the gorge and prevent a disaster.

As a result of heavy rains, several incidents occurred on the Black Sea coast.

August, a mudflow descended on a section of the M-27 federal highway Dzhubga - Sochi. Because of heavy rainfall A mudflow blocked the road at the Agoi Pass.

Chapter 4. Protection of territory and structures from mudflows

Protecting areas and structures from mudflows is a difficult task. It can only be solved with an integrated approach, i.e. with a combination of both engineering (active) and preventive measures. Otherwise, the formation of powerful mudflows and numerous destructions is possible.

4.1 Preventive measures

Preventive measures include measures that prevent the formation of mudflows or weaken their effect at the very beginning of their development. The list of these measures includes:

· stopping deforestation on mudflow-prone mountain slopes,

· reforestation and shrub planting,

Limitation of livestock grazing

· early release of existing reservoirs (moraine and glacial lakes),

· terracing of mountain slopes,

regulation of surface runoff

and other forest reclamation and agrotechnical measures.

4.2 Engineering protection

For engineering protection of territories, buildings and structures from mudflows, mudflow retention, mudflow passage, mudflow control and stabilizing structures and measures are used (SNiP 22-02-2003).

They are designed and erected to retain a mudflow in the upstream and to form mudflow reservoirs, pass mudflows through an object or bypass it, direct a mudflow through an object or bypass it, direct a mudflow into a mudflow passage structure, stop the movement of a mudflow or weaken it (cascade of dams, retaining walls, drainage devices, etc.).

4.2.1 Extract from SNiP 02/22/2003

Type of structure and event	Purpose of the structure, measures and conditions for their use
IMud-retaining
Concrete, reinforced concrete, masonry dams: spillway, through. Dams made of soil materials (solid)	Retention of debris flow in the upstream. Formation of mudflow reservoirs
IIMudflow checkpoints
Channels. Selespuski	Passing mudflows through or bypassing an object
IIISelena guides
Guide and containment dams. Spurs	Direction of mudflow into the mudflow control structure
IVStabilizing
Cascades of dams. Retaining walls. Drainage devices. Terracing of slopes. Agroforestry	Stopping the movement of a mudflow or weakening its dynamic characteristics
VDebris-preventing
Dams for regulation of mudflow-forming floods. Spillways on lake dams	Prevention of mudflows
VIOrganizational and technical Organization of surveillance and warning service	Forecast of mudflow formation

4.2.1.1 Debris retention structures

6.10 Mudflow retention dams, the destruction of which threatens catastrophic consequences, must be checked for the impact of a mudflow caused by a flood with a probability of exceeding 0.01%. In this case, the project should provide for the installation of surface mudflow structures that ensure the discharge of excess (compared to the calculated) volume of mudflow or raising the elevation of the dam crest, ensuring the accumulation of the entire volume of mudflow.

6.11 When designing mudflow retention dams, it is necessary to provide culverts for the passage of domestic river flow into the lower pool, as well as for the discharge of the water component of sediment-borne mudflows. In this case, the discharge flow should not exceed the critical mudflow flow determined for the area below the dam site.

6.12 As a rule, mudflow retention dams should be designed without anti-filtration devices and without gates on culverts. For the accumulation of mudflows, it is allowed to provide dams with a through design. Loads on through dams should be taken as on dead ones.

6.13 The elevation of the crest of blind mudflow retention dams made of soil materials above the level corresponding to the design volume of the mudflow storage facility should be taken to be no less than the height of the last mudflow shaft, determined at the maximum design mudflow flow rate and the average inclination angle, equal angle slope of the area in front of the mudflow reservoir. In this case, for mud-stone mudflows, the height of the mudflow levee at the dam is assumed to be equal to the depth of the mudflow at the entrance to the mudflow reservoir.

.2.1.2 Mudflow control structures

6.14 The main types of mudflow control structures are:

channels - for passing mudflows through populated areas, industrial enterprises and other objects, allowing mudflows to be passed through the object or bypassing it at the same level as them;

mudflows - for passing mudflows through linear objects (cars and railways, canals, gas pipelines, oil pipelines, etc.).

Note - The use of pipes to pass mudflows is not allowed.

6.15 The use of mudflow passage structures to pass mud-stone mudflows is allowed only if the longitudinal slope of the structure is at least 0.10.

6.16 The dimensions of mudflow passage structures with inlet and outlet sections, as well as the outlet tract, should be determined based on the condition of ensuring the necessary transporting capacity of the flow, in this case:

the slope of the bottom of the structures must be taken to be no less than the average slope of the approach section of the mudflow channel, the length of which is taken to be equal to at least twenty widths of the mudflow;

the width of the structures, as a rule, is assumed to be equal to the average width of the mudflow in the approach section of the mudflow channel;

the longitudinal axis of the mudflow control structure must be aligned with the dynamic axis of the mudflow; if it is necessary to rotate the structure, the angle between the axes should be no more than 8°;

the elevation of the walls (floors) of mudflow structures above the maximum level of mudflow should be taken equal to 0.2 N max, where H max - the maximum depth of the mudflow, but not less than 1 m for trays and not less than 0.5 m for channels.

6.17 It is recommended to orient the entrance section of the mudflow passage structures in such a way that the installation angle of the mating walls relative to the axis of the main channel does not exceed 11°.

mudflow engineering protection

Figure 5 Mudflow control structure at PC 5+80. Rosa Khutor plateau. Krasnodar region.

4.2.1.3 Sewer control structures

6.18 Debris flow control structures should be provided to direct the flow to mudflow passage structures, divert mudflow from the protected object or prevent erosion of the protected area.

6.19 The angles of rotation of guide dams in plan should be taken, as a rule, in accordance with the requirements of 6.17<#"648513.files/image013.gif">

.2.1.4 Stabilization structures

6.22 The design of slope stabilizing structures (retaining walls and drainage devices) should be carried out in accordance with the requirements of section<#"648513.files/image014.gif">

.2.1.5 Debris prevention structures

6.30 Dams are used in conditions when the source of formation of a rain or glacial mudflow is located below the source of formation of a mudflow-forming flood and the relief between these areas allows the creation of a regulating capacity. The dam must be equipped with a water outlet that ensures automatic emptying of the control tank with a flow rate not exceeding the mudflow, as well as a catastrophic spillway.

The required capacity of the control tank should be determined by the volume of the flood with a probability of exceeding 1% minus the volumes discharged into the downstream during the period of accumulation of this flood.

6.31 Spillways should be implemented to prevent lake outbursts. The type of spillway (trench, siphon, tunnel, etc.) is determined by the construction conditions and the nature of the lake dam.

Spillways should be designed for discharge with a probability of exceeding 2%.

In areas of settlements and individual structures located in the zone of proluvium deposition, diversion channels are installed, guide dams are installed, and river beds are taken into high stone banks that limit the spread of the mudflow. To protect road structures, the most efficient are mudflow drains in the form of reinforced concrete and stone chutes that allow mudflows to pass above or below structures.

The most reliable means for protecting settlements and territories from possible mudflows are high, massive dams and dams that block the beds of mountain rivers. An example is the 115 m high dam built in 1971 on Malaya Almaatinka in the Medeo tract. The dam was created from local stone materials using a directed explosion method, followed by building up the blasted material in the form of an embankment. With its help, in 1973, a catastrophic mudflow with a volume of up to 4.0 million m3 of mud-stone mass and up to 1.5 million m3 of flood water was stopped. Thus, the city of Alma-Ata was saved from great destruction and loss of life.

It must be emphasized that the fight against mudflows is one of the most important issues of protection and rational use of the geological environment. The design and construction of anti-mudflow structures without proper consideration of the features of this dangerous geological process and without forecasting its possible negative consequences may not only be ineffective, but also cause significant harm to the environment.

Bibliography

1. L.V. Peredelsky, O.E. Prikhodchenko "Engineering Geology".

2. V.P. Ananyev, L.V. Peredelsky "Engineering geology and hydrogeology".

V.P. Ananyev, A.V. Potapov "Engineering Geology"

A.I. Artsev "Engineering-geological and hydrogeological research for water supply and sanitation."

V.F. Perov "Mudflow phenomena. Terminological dictionary"

Mudflows consist of large masses of destroyed rocks in a loose state, which accumulate over years at the bottom of gorges and steep slopes. During intense rainfalls or during the outburst of glacial lakes located above, mud-stone mudflows are formed and flow down, destroying everything in its path.
In mountainous areas, heavy rainfall or rapid snowmelt causes the formation of temporary torrential streams. A powerful stream flowing down steep slopes has enormous force and, like mountain rivers, carries along small rock fragments, large blocks and boulders. Acting like a battering ram with captured debris, such a stream destroys the ledges and unevenness of mountains encountered along the way, carries them along with it and becomes more and more saturated with stone material.

Next, the flow captures the upper layers of fine-clastic material and soils and gradually turns from water into mud-stone. Such a flow is called mudflow or silt. Temporary mud-stone flows are widespread in the Caucasus and Central Asia. The content of transported material in debris flows is very high and sometimes exceeds the water content. Erupting from a mountain gorge onto the plain, the mudflow quickly loses speed and spreads over a relatively large area in the form of a fan. Water from a mudrock flow filters to its base, and the transported rock material settles to form a fan or dry delta.

Mudflows are a mixture of soil, stones and water with a fairly high density of 1.2-1.9 t/m³, which flows down the beds of various mountain rivers and dry valleys after rainstorms at a speed of up to 6 m/s. When leaving the ravine, in places where the slope decreases, the velocity of the mudflow also decreases and an alluvial cone is formed.

The detrital mass brought by such a flow consists of almost unrounded fragments and is completely unsorted: among large blocks and boulders there are gravel-sand-clay particles. Deposits of debris flow cones are called proluvial or proluvium. Debris flows pose a great danger to populated areas located in their zone of action. The famous mudflow of 1921, which burst out of a mountain gorge near the city of Alma-Ata, demolished all the buildings located at the foot of the mountain. Then he burst into the city, turning the streets into raging mud-stone rivers.

Houses were torn off their foundations and carried away along with people. A mass of stone material of about 1.5 million tons was carried out onto the city.

Picture 1. Destruction of populated areas caused by mud-stone flows

Mudflows arise suddenly and last a relatively short time, lasting a few hours, but are capable of forming significant volumes of mud-stone materials that are washed away in one mudflow. A mudflow is capable of washing away and carrying stones with a diameter of up to 1.5 meters. Considering the high speed of the mudflow and the volume of transferred stones, the protection of cities and villages, as well as various structures located in the action area, is a big problem.

To solve such problems, it is necessary to erect expensive and complex structures such as retaining walls or dams. Depending on how much water the mud-stone flows contain, the mudflow can move as a homogeneous viscous mass or as a turbulent flow of water, stones and mud. The stream carries along a huge number of stones of various diameters and washes away huge volumes of soil from the surface. In a mudflow, small stones move in suspension, while larger ones move by rolling along the bottom of the thalweg.

Methods for protecting buildings from mudflows

Mountain rivers and mudflows are capable of carrying stones of enormous size and in large quantities, which can pose a threat not only to various structures and communications such as bridges, roads, but also to nearby cities. If construction is inevitable in the area where mudflows form, various measures are taken to protect structures from mudflows.

For example, bridges are built with spans that do not restrict the flow of mudflows, and single-column supports are used. The openings of bridges are significantly increased, since it is difficult to predict the volume of mudflows, which vary depending on the amount of precipitation. The openings of small bridges quickly become clogged with sediment and in this case the mudflow flows over the bridge and embankment.

In order to protect cities and large structures of great importance, sediment-retention dams are installed on the upper side of mountain slopes. Such dams slow down the speed of mudflows and cause sediment deposition. There are two types of dams: continuous and intermittent. Continuous dams are built when the width of the river bed exceeds 100 meters.

In this case, the required length of the dam depends on the width of the channel and also on the size of the particles that mudflows deposit. The length of the dam in this case is determined by the formula:

L=b*B, where b is the coefficient of restriction of the channel by the dam, B is the width of the channel.

Dams of intermittent type are built when the width of the channel is up to one hundred meters. In this case, the length of the dam is determined by the formula and the opening of the dam is determined depending on the passage of the required amount of mudflows with a given frequency. In the transverse profile, such dams are built with a trapezoidal cross-section. The width of the dam at the top ranges from 0.5 to 2.0 meters, depending on the size of the transferred stones and the intensity of the mudflow.

Figure-2. Construction of partition walls to combat mudflows

A measure to combat mudflows is, first of all, the restoration of vegetation cover with a powerful root system, as well as the installation of partition walls (Figure 2). The construction of terraces can be used as an anti-mudflow measure (Figure 3).

Figure-3. Terracing scheme to combat mudflows

Along the terraced slope, the mudflow will flow from step to step, ending up in the ditches prepared for it. Recently, dams constructed using the directed explosion method have been used to combat mudflows. For example, such a dam was created in 1966 in the Medeo tract in the mountains near Alma-Ata. With the help of an explosion, almost 2 million tons of rock were placed into the dam. Along with mudflows, there are channelless flows from slopes. A complex of loose formations that accumulate at the foot of mountains as a result of temporary mountain flows washing away the clastic material that appears during the weathering of the bedrock composing these mountains is called proluvium.

Table 1. Comparison of properties of water-continental sediments

Proluvium is characterized by poorly sorted and weakly rounded fragments. It forms alluvial cones that can merge into one strip bordering the base of the horizon. The difference is in power, duration of action and direction water flows determines the difference in the properties of the rocks they deposit.

This difference is most clearly visible from the comparison shown in Table 1. From Table 1 it is clear that with a fairly close mineralogical and granulometric composition Various types deposits of flowing surface water have different properties. This should be taken into account when designing and constructing structures.

Classification of mudflows

The study of the formation and action of mudflows made it possible to classify them according to a number of characteristics. According to the research of E.K. Rabkova, it is possible to distinguish between cohesive or structural mudflows, turbulent-flowing water-stone and turbulent-flowing mud-stone. Structural or cohesive mudflows form in mountainous areas. The geological structure of the drainage basin necessarily contains clay rocks and clays. In addition, there are rocks that can produce screes and difficult-to-crush fragments: limestones, shales, crystalline rocks.

The volumetric mass of the flow is very high and amounts to 1.9-1.6 t/m³. Clay fractions make up no more than 25-30% of the solid part of the flow. The rest consists of sand, crushed stone, gravel and boulders. Water is included in the mudflow mass as one of the components. To maintain the movement of the flow, a straight direction is necessary, without bends. Such a flow moves as one structural whole and, when stopped, freezes without breaking up into its component parts. Structural flows destroy all structures and other obstacles encountered along the entire width of the movement. With slopes of 0.05-0.06 degrees on the alluvial cone, the bottom of the channel is covered with a layer of frozen mudflow.

Turbulent-flowing water-stone mudflows also form in mountainous zones. The drainage area of ​​such flows is composed of intrusive rocks, as well as limestones, sandstones and well-cemented conglomerates. The presence of coarse material: gravel, pebbles, coarse sand is also possible. The presence of clayey rocks is not significant. The volumetric mass of the mudflow in such streams it is 1.6-1.3 t/m3. The stream is poorly saturated with fine earth. Individual boulders and boulders reach 1-2 m in circumference. The nature of the movement of individual flow waves is pulsating and jammed. The presence of large fragments and the jammed nature of the movement determines a large destructive force. Some sorting of the carried out material is possible on the alluvial cone.

Turbulent-flowing mud-stone mudflows are formed in both mountain and foothill zones. The drainage area is characterized by a predominance of fine-clastic and clastic material, sandy loam and loam. There is a large amount of crushed stone and pebbles. The volumetric mass of the mudflow is relatively small and amounts to 1.4-1.05 tons /m³. The flow is saturated with suspended fine fractions and pebbles drawn along the bottom.

The deposition of large masses on the alluvial cone leads to the flow overflowing the barriers, accompanied by the destruction of roads, bridges and other structures. Unlike structural flows, destruction occurs not by impact, but by erosion. The nature of the flow movement is congestion-free. At the removal cone, some sorting of the transported material by size occurs.

Table 2. Main types of mudflows and possible causes

Main types of mudflows and possible causes

Classification of mudflows according to the granulometric composition of the solid component:

1. Water-stone - is a mixture of dirty water with stones large sizes(rock fragments, boulders, etc.) with a volumetric weight of 1.1–1.5 t/m³. The water-rock flow is formed mainly in the zone of dense rocks.

2. Mud - is a mixture of dirty water with particles of clay and silty soil in the solid phase with a slight concentration of stones. Volumetric weight ranges from 1.5-2.0 t/m³.

3. Mud-stone flow is a mixture of water with fine earth particles and mostly small stones. The volumetric weight of such a flow is 2.1–2.5 t/m³.

4.Water-snow-rock consists mainly of water, snow avalanches and stones of different sizes. Such a mudflow is very heavy and the mudflow reaches up to 5–12 t/m².

Classification of mudflows by genesis:

1. Alpine type - this type is characterized by seasonal rapid melting of snow (Canada, USA, Andes, Himalayas, Alps)

2. Desert type - found mainly in semi-arid or arid areas that experience sudden heavy rainfall. Most often observed in areas such as Arizona, Nevada, California.

3. Lahars are mud flows of volcanic origin that appear on the slopes of volcanoes after heavy torrential rains.

The following mudflows are distinguished based on their frequency:

a) high activity (repeated within 3-5 years and maybe more often)

b) average activity (repeated within 6-15 years)

c) low mudflow activity (repeated once every 16 years).

By impact on structures:

1. Low-power - they create small erosions at the base and clog the culverts of structures.

2. Medium-power - they create strong erosion at the base of bridges and culverts, completely clog the openings of culverts. They can also demolish foundationless structures.

3. Powerful and has great destructive power. It can demolish bridge trusses, supports of bridges and overpasses, and also destroy roads.

4. Catastrophic - completely destroys buildings and sections of roads.

By water source:

1. Rain - such mudflows are typical for low-mountain and mid-mountain mudflow basins that do not have glacial feeding. The conditions for the formation of these mudflows are heavy rainfall, washing away destroyed rocks from the slopes.

2. Glacial - they are characterized by low-mountain and mid-mountain mudflow basins that do not have glacial feeding. They are formed due to heavy precipitation that can wash away the products of rock destruction.

3. Volcanogenic - formed mainly during earthquakes. Sometimes in some cases they are formed during a volcanic eruption.

4. Associated mudflows - can consist of water, sandy and clayey soil particles. The mudflow moves as one whole and does not follow the bends of the river bed, but flows over the banks. In some cases, it can destroy and straighten river beds.

5. Unbound flows are capable of moving at high speed, while constant rolling of stones and abrasion occurs due to frequent collisions. The flow usually follows the river bed, destroying it in places and repeating its bends.

By volume of transferred solid mass:

According to the main factors of occurrence

1. Zonal manifestation. They are formed due to heavy precipitation and are of a zonal nature. As a rule, mudflows occur systematically along the same paths.

2. Regional manifestation. They are formed due to geological processes. As a rule, the paths of movement of mudflows are not constant and the flow is episodic.

3. Anthropogenic. Occur as a result of human economic activity.

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Classification

By altitude position

According to the geomorphological structure of the basins

For reasons of occurrence

According to the degree of saturation with sediment and its fractional composition

Mud mudflows

Mud-stone mudflows

Water-rock (alluvial) mudflows

Emergence

Sometimes mudflows occur in the basins of small mountain rivers and dry ravines with significant (at least 0.10) thalweg slopes and in the presence of large accumulations of weathering products.

Characteristics

Mudflows are characterized by the advancement of its frontal part in the form of a shaft of water and sediment, or more often by the presence of a series of successively shifting shafts. The passage of a mudflow is accompanied by significant reformations of the riverbed.

Mudflows

Debris flows coming from volcanoes are called lahars.

The average speed of mudflows is 2-4 m/s, reaching 4-6 m/s, which causes their great destructive effect. Along their path, streams carve deep channels that are usually dry or contain small streams. Mudflow material is deposited in the foothill plains.

Messengers

Connected people include mud-stone streams, in which water is practically not separated from the solid part. They have a large volumetric weight (up to 1.5-2.0 t/m3) and great destructive power. Water-stone flows are classified as incoherent. Water transports debris and, as its velocity decreases, deposits it in the channel or fan area on the foothill plain. The volumetric weight of water-rock mudflows is 1.2-1.5 t/m3.

The following zones are distinguished in the mudflow basin:

1. Origin zone (feeding)
2. Transit zone
3. Accumulation zone.

Fighting mudflows

Mudflows can cause enormous destruction. The fight against mudflows is carried out mainly by securing soil and vegetation cover and constructing special hydraulic structures.

To combat mudflows, preventive measures and construction of engineering structures are carried out. The use of certain control methods is determined by the zones of the mudflow basin. Preventive measures are taken to prevent the occurrence of a mudflow or weaken its effect at the very beginning of the process. The most radical remedy is afforestation on mudflow-prone mountain slopes. The forest regulates flow, reduces the mass of water, and cuts streams into separate weakened streams. It is forbidden to cut down forests or disturb the turf cover in the catchment area. Here it is advisable to increase the stability of slopes by terracing, intercept and drain water with upland ditches and earthen ramparts. In mudflow channels, dams have the greatest effect. These structures made of stone and concrete, installed across the riverbed, delay the mudflow and take away some of the solid material from it. Half-dams push the flow toward the shore, which is less susceptible to rupture. Mud catchers are used in the form of pits and basins laid in the path of flows; they build bank-protecting retaining walls that prevent erosion of the banks of the riverbed and protect buildings from the impact force of mudflows. Guiding dams and mudflow reservoirs are effective. Dams direct the flow in the desired direction and weaken its effect. At the sites settlements and individual structures located in the proluvium deposition zone, diversion channels are constructed, guide dams are installed, and river beds are taken into high stone banks that limit the spread of the mudflow. To protect road structures, the most efficient are mudflow drains in the form of reinforced concrete and stone chutes that allow mudflows to pass above or below structures.

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See what “Mudflow” is in other dictionaries:

- (mudflow) a rapid channel flow, consisting of a mixture of water and rock fragments, suddenly appearing in the basins of small mountain rivers. S.p. characterized by a sharp rise in level, pulsating (wave) movement, short duration... ...

mudflow- A turbulent mud or mud-stone flow with great destructive power that suddenly appears in the mountains as a result of the breakthrough of water accumulated as a result of heavy rains, intense snow melting, the breakthrough of lakes or pulsating movements... ... Dictionary of Geography

Mudflow (from Arabic, sayl stormy stream), a stormy, sudden flood. in mountain river basins, carrying a large stake in mud or mud. sediment S. p. arise as a result of rainfall or rapid snowmelt; have great destroy... Big Encyclopedic Polytechnic Dictionary

mudflow, mudflow- mudflow, debris flow mudflow, mudflow is a rapid channel flow, consisting of a mixture of water and rock fragments, suddenly appearing in the basins of small mountain rivers. S.p. characterized by a sharp rise in level, pulsating (wave) ... ...

mudflow (mudflow)- Mountain channel flow, consisting of a mixture of water in a coherent (bound by monodisperse silt-clay particles) or incoherent state, rock fragments, tree remains (if they are present along the path of the mudflow). Note Most often... Dictionary-reference book of terms of normative and technical documentation

mudflow source- mudflow original site MURDFLOW CHAMBER is a section of a mudflow basin, usually in the upper reaches, where the origin of a mudflow occurs. With the erosion and breakthrough mechanism of nucleation of s.o. is fixed by the place of formation of a mudflow wave in the channel, below which... Mudflow phenomena. Terminological dictionary

mudflow basin- mudflow basin MUSDFLOW BASIN a drainage basin within which mudflows are formed, and their movement occurs along the main channel. S.b. serve as catchments of small and medium-sized watercourses (temporary and permanent) with an area from 1–2 to 100–200... ... Mudflow phenomena. Terminological dictionary

SEL, I, m. A stormy mud-stone stream that occurs in the mountains during heavy rains or melting snow. Came down from the mountains. Dictionary Ozhegova. S.I. Ozhegov, N.Yu. Shvedova. 1949 1992 … Ozhegov's Explanatory Dictionary

A section of a debris flow basin, usually in the upper reaches, where a debris flow originates. With the erosion and breakthrough mechanism of O.s. the location of the formation of a mudflow wave in the channel is recorded, below which there are continuous traces... ... Dictionary of emergency situations

snow-water stream- Mudflow, represented by a mixture of snow and water, as well as rock fragments. Syn.: snow mudflow... Dictionary of Geography

Mudflow is a mud or mud-stone flow that suddenly forms in the beds of mountain rivers as a result of rainfall, rapid melting of glaciers or seasonal snow cover. Moving at high speed, mudflows often cause major destruction in their path. In Peru in 1970, a mudflow destroyed several cities, killing more than 50 thousand people, leaving 800 thousand homeless. All movements of rocks and clay masses are preceded by various signals: the formation of new cracks and crevices in the soil; unexpected cracks in internal and external walls, water pipes, asphalt; falling stones; the occurrence of a strong roar in the upper reaches of mudflow-prone watercourses, which drowns out other noises; a sharp drop in water levels in rivers; manifestation of a cloud of mud dust accompanying the “head” of the mudflow.

Mudflows are floods with a very high concentration of mineral particles, stones and rock fragments (from 10-15 to 75% of the flow volume), occurring in the basins of small mountain rivers and dry ravines and caused, as a rule, by rainfall, less often by intense snow melting, as well as the breakthrough of moraine and dam lakes, landslides, landslides, and earthquakes. The danger of mudflows lies not only in their destructive power, but also in the suddenness of their appearance. Approximately 10% of the territory of our country is subject to mudflows. In total, about 6,000 mudflow streams have been registered, more than half of which are in Central Asia and Kazakhstan.

According to the composition of the transported solid material, mudflows can be mud (a mixture of water with fine earth with a small concentration of stones, volumetric weight y = 1.5-2 t/m3), mud-stone (a mixture of water, pebbles, gravel, small stones, y = 2 ,1-2.5 t/m3) and water-stone (a mixture of water with predominantly large stones, y==1.1-1.5 t/m3).

Many mountainous regions are characterized by the predominance of one or another type of mudflow in terms of the composition of the solid mass it transports. Thus, in the Carpathians, water-stone mudflows of relatively small thickness are most often found, in the North Caucasus - mainly mud-stone mudflows, in Central Asia - mud flows. The flow speed of a mudflow is usually 2.5-4.0 m/s, but when the jams break through, it can reach 8-10 m/s or more. The consequences of mudflows can be catastrophic. So, on July 8, 1921, at 21:00, a mass of earth, silt, stones, snow, sand, driven by a mighty stream of water, collapsed on the city of Alma-Ata from the mountains. This stream demolished the dacha buildings located at the foot of the city along with people, animals and orchards. A terrible flood burst into the city, turning its streets into raging rivers with steep banks of destroyed houses. The horror of the disaster was aggravated by the darkness of the night. There were cries for help that were almost impossible to say. Houses were torn off their foundations and, along with people, were carried away by a stormy stream.

By the morning of the next day the elements had calmed down. Material damage and loss of life were significant. The mudflow was caused by heavy rainfall in the upper part of the river basin. Malaya Almatinka. The total volume of mud-stone mass was about 2 million m3. The flow cut the city with a 200-meter strip.

Methods of dealing with mudflows are very diverse. This is the construction of various dams to retain solid runoff and pass a mixture of water and small fractions of rocks, a cascade of dams to destroy a mudflow and free it from solid material, retaining walls to strengthen slopes, upland runoff interception and drainage ditches to divert runoff to nearby watercourses, etc. There are currently no methods for predicting mudflows. At the same time, for some mudflow areas, certain criteria have been established to assess the likelihood of mudflows occurring. Thus, for areas with a high probability of mudflows of storm origin, the critical amount of precipitation is determined for 1-3 days; mudflows of glacial origin (i.e., formed during outbursts of glacial lakes and intraglacial reservoirs) - critical average temperature air in 10-15 days or a combination of these two criteria

Sel is something between a liquid and a solid mass. This phenomenon is short-term (usually it lasts 1-3 hours), characteristic of small watercourses up to 25-30 km long and with a catchment area of ​​up to 50-100 km2.

The mudflow is a formidable force. The stream, consisting of a mixture of water, mud and stones, rapidly rushes down the river, uprooting trees, tearing down bridges, destroying dams, stripping the slopes of the valley, and destroying crops. Being close to a mudflow, you can feel the shaking of the earth under the impact of stones and blocks, the smell of sulfur dioxide from the friction of stones against each other, and hear a strong noise similar to the roar of a rock crusher.

The danger of mudflows lies not only in their destructive force, but also in the suddenness of their appearance. After all, rainfall in the mountains often does not cover the foothills, and mudflows appear unexpectedly in inhabited areas. Due to the high speed of the current, the time from the moment a mudflow occurs in the mountains to the moment it reaches the foothills is sometimes calculated in 20-30 minutes. The entire area of ​​debris flow generation and impact is called mudflow basin .

The type of mudflow is determined by the composition of the mudflow-forming rocks. Basic types of mudflows :

water-stone(mixture of water with predominantly large stones, y==1.1-1.5 t/m3)

mud(a mixture of water with fine earth with a small concentration of stones, volumetric weight y = 1.5-2 t/m3)

mud-stone(mixture of water, pebbles, gravel, small stones, y==2.1-2.5 t/m3)

For a mudflow to occur, the simultaneous coincidence of three mandatory conditions :

the presence on the slopes of the mudflow basin of a sufficient amount of easily transportable rock destruction products (sand, gravel, pebbles, small stones);

the presence of a significant volume of water to wash away stones and soil from the slopes and move them along the riverbed;

sufficient slope steepness (at least 10-15°) of the mudflow basin and water flow (mudflow bed).

Direct the impetus for the occurrence of mudflows can be :

intense and prolonged downpours;

rapid melting of snow and glaciers;

earthquakes and volcanic activity, etc.

Mudflows often result from anthropogenic factors: deforestation carried out on slopes, blasting, quarrying, mass construction.

How to prepare for a mudflow

Usually the places where mudflows can occur are known. Before going to the mountains, study these places along your route and avoid them, especially after heavy rains. Always remember that it is almost impossible for someone caught in a mudflow to escape. You can only escape from a mudflow by avoiding it. Before leaving home, during early evacuation, turn off electricity, gas and water supply. Close doors, windows and vents tightly.

Early measures to prevent mudflows

In mudflow-prone areas, anti-mudflow dams and dams are constructed to retain solid runoff and pass a mixture of water and fine rock fractions, a cascade of dams to destroy the mudflow and free it from solid material, retaining walls to strengthen slopes, upland runoff interception ditches and drainage ditches to divert runoff to nearby watercourses, etc., bypass canals are constructed, the level of mountain lakes is reduced, the soil on the slopes is strengthened by planting trees, observations are carried out, a warning system is organized and evacuation is planned.

How to act in case of a mudflow

Having heard the noise of an approaching mudflow, you should immediately rise from the bottom of the ravine up the drainage, at least 50-100 m. You must remember that heavy stones can be thrown from the roaring flow over long distances, threatening your life.

Actions after a mudflow

Provide assistance to the victims and assistance to the formations and authorities clearing debris and drifts along the path of the mudflow and in places where the bulk of the mudflow was carried out. If you are injured, try to provide yourself with first aid. If possible, the affected areas of your body should be kept in an elevated position, ice (wet cloth) and a pressure bandage should be applied to them. See your doctor.

There are currently no methods for predicting mudflows. At the same time, for some mudflow areas, certain criteria have been established to assess the likelihood of mudflows occurring. Thus, for areas with a high probability of mudflows of storm origin, the critical amount of precipitation is determined for 1-3 days, mudflows of glacial origin (i.e., formed during outbursts of glacial lakes and intraglacial reservoirs) - the critical average air temperature for 10-15 days or a combination of these two criteria

Composition of mudflows

Based on the composition of these materials, mudflows can be:

Water-stone (water with large stones and rock fragments);

Mud (a mixture of water with fine earth and small stones);

Mud-stone (a mixture of water, fine earth, gravel, pebbles, stones).

Therefore they are very heavy. One cubic meter of mudflow (which is approximately the volume of your workplace including your desk) weighs from 1200 to 2000 kg. In other words, the density of the mudflow, depending on its structure, ranges from 1.2 to 2.0 t/cub.m.

The water in the river is also heavy, but it flows smoothly. And the mudflow rushes from the mountains at the speed of a running person, and sometimes faster (up to 40 km per hour). Therefore, the impact of a mudflow is equivalent to the impact of a moving bus, reaching a value of 5-12 t/sq.m. m. Moreover, after the impact, the object is not thrown away, but is flooded by a rushing mud-stone mass and is pulled further downstream in the thick of a multi-meter stream. It is possible to escape in rare cases, when the speed and depth of the flow decrease significantly on gentle turns and there are no large stones that cause fatal injuries.

Places of origin of mudflows

Unlike landslides and landslides that occur throughout almost the entire territory of our country, mudflows originate only in mountainous areas and move mainly along river beds or along gullies (ravines) that have significant slopes in their upper reaches.