We have already noted that in the process of the water cycle in nature, dangerous phenomena hydrological nature. The most common and frequently recurring of these are floods.

According to the Russian Ministry of Emergency Situations, floods in terms of frequency, area of ​​distribution, and total average annual damage rank first in Russia among the known ones. natural disasters. They rank second after earthquakes in terms of the number of human casualties.

In Russia, floods threaten almost 40 cities and several thousand other settlements. The frequency of floods on average ranges from once every 5-10 years to once every 15-20 years. But there are cities where floods occur once every 2-3 years (Ufa, Orsk, Kursk and a number of others).

What is a flood?

Flood- this is a significant flooding of an area as a result of rising water levels in a river, lake, reservoir or sea, causing material damage to the economy, social sphere and natural environment. Floods occur as a result of an abundant and concentrated influx of water during the melting of snow and glaciers, long-term intense rainfall in river basins, blockage of river channels with melting ice (jams) or clogging of river channels with internal, newly formed ice (zazhor), surge of water by wind in the sea mouths of rivers .

One of the many floods in St. Petersburg

Flooding of an area with water that is not accompanied by damage environment, is called the overflow of a river, lake or reservoir.

Types of floods

Floods can be caused by various reasons related to the characteristics of river water flow and its changes in different times year. Water flow in rivers is influenced by melting snow and ice, rainfall and wind surges at river mouths. Depending on these reasons, several types of floods are distinguished.

1. Floods associated with water runoff during high water.

   High water- this is an increase in the volume of water in the river that is repeated annually in the same season, which is accompanied by its waters overflowing the banks and flooding the river floodplain. The flood of lowland rivers in places with a temperate climate is caused by spring snowmelt (spring flood). Floods on rivers originating high in the mountains are caused by the melting of snow and glaciers in summer time(summer flood). This type of flood is characterized by a significant and rather long-term rise in the water level in the river.

2. Floods formed by high water.

   Flood- this is a rapid, short-term and non-periodic rise in water level, resulting from the rapid melting of snow, glaciers, and heavy rains. Significant flooding may cause flooding. This type of flood is characterized by an intense, relatively short-term rise in water levels.

3. Floods caused by high resistance that the water flow encounters in the river bed. They occur during ice jams and ice jams in the river.

   Congestion- This is an accumulation of ice in a river bed, limiting its flow. Jams usually form at the end of winter and in spring when rivers open up. Most often, congestion occurs on rivers flowing from south to north (Northern Dvina, Pechora, Lena, Yenisei, Irtysh).

   Zazhor- This is a phenomenon similar to ice jams, but it is observed on rivers at the beginning of winter. Ice jams form on rivers during the formation of ice cover. The jam occurs due to the accumulation of loose ice and small ice floes in the riverbed and its involvement under the edge of the formed ice cover, which impedes the free flow of water and causes a rise in the water level in the river upstream. The Angara and Neva rivers are noted in terms of the frequency of ice floods and the magnitude of water rise.

4. Floods associated with wind surges of water on the shores of large lakes and at the mouths of large rivers. Such floods occur on the windward shore of a reservoir when, under the influence of a strong wind on the water surface, the water level rises.

All of the above types of floods, depending on their scale and the material damage caused, are divided into low, high, outstanding and catastrophic.

Low (small) floods observed mainly on lowland rivers. The frequency of their recurrence is approximately once every 5-10 years. These floods cause minor material damage and hardly disrupt the lives of the population.

High (large) floods are accompanied by significant flooding, cover large areas of river valleys and disrupt the livelihoods of the population. In densely populated areas, floods often lead to the need for partial evacuation of people and cause significant material damage. The recurrence rate of major floods is approximately once every 20-25 years.

Outstanding Floods cause flooding of vast territories, paralyze the economic activity of the population, and cause great material damage. In this case, there is a need for mass evacuation of the population from the flood zone. Such floods occur approximately once every 50-100 years.

Catastrophic floods cause flooding of large areas within one or more river systems. In the flood zone, human life is completely paralyzed. Such floods lead to enormous material losses and loss of life. They occur approximately once every 100-200 years.

The scale of the consequences of a flood depends on the height and duration of dangerous water levels, the speed of water flow, the area of ​​flooding, the time of year and the population density in the flooded area.

History knows many examples of catastrophic floods.

The picture of the oldest of them was restored based on archaeological research.

It was found that the Black Sea was a freshwater lake 12,000 years ago, and 7,500 years ago, due to global warming on Earth, melting glaciers and rising water levels in the World Ocean, it was filled with water Mediterranean Sea and turned into the salty Black Sea.

Modern American geologists V. Pitman and V. Rhine, putting together everything known to science facts about the breakthrough of ocean waters 7.5 thousand years ago were able to reproduce the picture of a hydrological catastrophe.

The waters of the Mediterranean Sea rushed into the passage between Asia and Europe. For about a year, water in this place fell from a height of 120 m. The lake, turned into the Black Sea, overflowed its banks and flooded almost one hundred thousand square kilometers of land, mainly the northwestern coast. A new Sea of ​​Azov was formed next to the Black Sea. In the east, the waters reached the foot of the Caucasus Range. For at least three hundred days the waters rushed through the valley, where the Bosphorus Strait is now located, connecting the Black and Marmara Seas. Every day 50 cubic kilometers of water flowed through it, and the level of the Black Sea rose by 15 centimeters every day.

On the northern and western coasts of the Black Sea, the disaster took on a tragic character. Every day the water here moved 400 m. It was flooded large area land.

World Flood. The death of all living things. Engraving by Gustave Doré

Mortal danger forced people to quickly leave their homes, thereby causing a powerful movement of human masses. The people who escaped the stream forever remembered the terrible days and nights of fleeing from the water rushing behind them.

This catastrophe may have been identified later with the Great Flood described in the Bible.

Test yourself

1. Define the natural phenomenon of flooding.
2. List the main types of floods.
3. What natural hydrological phenomena can cause floods?

After classes

In your safety diary, give examples of floods in Russian Federation that occurred on various reasons(flood, flood, surge winds). Indicate their consequences and measures to protect the population. Examples can be found using the Internet and the media.

Flood

Flood in Asheville, North Carolina in July 1916

Flood- flooding of the area as a result of rising water levels in rivers, lakes, seas due to rains, rapid snow melting, wind surge of water on the coast and other reasons, which damages people’s health and even leads to their death, and also causes material damage.

Floods are often caused by an increase in the water level in the river due to blockage of the riverbed with ice during ice drift (jam) or due to clogging of the riverbed under a stationary ice cover with accumulations of inland ice and the formation of an ice plug (jag). Floods often occur under the influence of winds, driving water from the sea and causing an increase in the level due to the retention of water brought by the river at the mouth. Floods of this type were observed in Leningrad (1824, 1924), the Netherlands ( 1953 ). On sea coasts and islands, flooding may occur as a result of inundation coastal strip a wave generated by earthquakes or volcanic eruptions in the ocean (see Tsunami). Similar floods are not uncommon on the shores of Japan and on other islands Pacific Ocean. Floods can be caused by breaches of dams and protective dams.

Floods occur on many rivers in Western Europe - the Danube, Seine, Rhone, Po and others, as well as on the Yangtze and Yellow Rivers in China, the Mississippi and Ohio in the USA. In the USSR, large floods were observed on the Dnieper () and Volga ( and ) rivers.

Congestion, gluttony floods (congestion, gluttony)

Great resistance to water flow in certain sections of the river bed, which occurs when ice material accumulates in narrowings or bends of the river during freeze-up ( for and ors) or ice drift ( for T ors). For T ore floods are formed at the end of winter or beginning of spring. They are characterized by a high and relatively short-term rise in the water level in the river. For and ore floods are formed at the beginning of winter and are characterized by a significant (but less than during a jam) rise in the water level and a longer duration of the flood.

Surge floods (surges)

Wind surges of water in sea estuaries and on windy areas of the coast of seas, large lakes, and reservoirs. Possible at any time of the year. They are characterized by a lack of periodicity and a significant rise in water levels.

Floods (flooding) resulting from dam failures

An outflow of water from a reservoir or reservoir, formed when a pressure front structure (dam, dike, etc.) breaks through or during an emergency release of water from a reservoir, as well as when a natural dam breaks through, created by nature during earthquakes, landslides, landslides, or glacier movement. Characterized by the formation of a breakthrough wave leading to flooding large territories and destruction or damage to objects encountered along the path of its movement (buildings, structures, etc.)

Classification of floods depending on the scale of distribution and frequency

Low (small)

They are observed on lowland rivers. Covers small coastal areas. Less than 10% of agricultural land is flooded. They hardly disturb the rhythm of life of the population. Repeatability 5-10 years. That is, they cause minor damage.

High

Cause significant material and moral damage, covering relatively large land plots river valleys, flood approximately 10-20% of agricultural land. They significantly disrupt the economic and everyday life of the population. Lead to partial evacuation of people. Repeatability 20-25 years.

Outstanding

They cause great material damage, covering entire river basins. Approximately 50-70% of agricultural land is flooded, some populated areas. They paralyze economic activity and sharply disrupt the everyday life of the population. Lead to the need for mass evacuation of the population and material assets from the flood zone and protection of the most important economic facilities. Repeatability 50-100 years.

Catastrophic

They lead to loss of life, irreparable environmental damage, and cause material damage, covering vast territories within one or more water systems. More than 70% of agricultural land, many settlements, industrial enterprises and utilities are flooded. The economic and production activity, changes temporarily way of life population. The evacuation of hundreds of thousands of people, an inevitable humanitarian catastrophe requires the participation of the entire world community, the problem of one country becomes a problem of the whole world.

Types

• Flood is a periodically recurring, rather prolonged rise in water levels in rivers, usually caused by spring melting of snow on the plains or rainfall. Floods low-lying areas.

A flood can become catastrophic if the infiltration properties of the soil have significantly decreased due to its oversaturation with moisture in the fall and deep freezing in harsh winter. Spring rains can also lead to increased flooding, when its peak coincides with the peak of the flood.

• Flood is an intense, relatively short-term rise in the water level in a river, caused by heavy rains, downpours, and sometimes rapid melting of snow during thaws. Unlike floods, floods can occur several times a year. A particular threat is posed by the so-called flash floods associated with short-term but very intense downpours, which also occur in winter due to thaws.
• A jam is a accumulation of ice floes during the spring ice drift in narrowings and bends of the river bed, restricting the flow and causing a rise in the water level in the place where the ice accumulates and above it.

Congestion occurs due to non-simultaneous opening big rivers, flowing from south to north. The exposed southern sections of the river are spring-loaded in their flow by the accumulation of ice in northern regions, which often causes a significant increase in water levels.

• Zazhor is an accumulation of loose ice during freeze-up (at the beginning of winter) in narrowings and bends of the river bed, causing water to rise in some areas above it.
• Wind surge is a rise in water level caused by the action of wind on the water surface, occurring at the mouths of large rivers, as well as on the windward shores of large lakes, reservoirs and seas.
• Flood due to a breakthrough in hydraulic structures ( hydrodynamic accident) is an incident associated with failure (destruction) hydraulic structure or parts thereof, followed by uncontrolled movement of large masses of water.

Reasons

Long rains

Flood in Biysk caused by abnormally long rains (more than 72 hours), 2006

Summer rains falling on the Abyssinian Highlands cause the Nile to overflow every year, flooding the entire valley in its lower reaches.

Snow melting

Intense melting of snow, especially when the ground is frozen, leads to flooding of roads.

tsunami wave

On sea coasts and islands, floods can occur as a result of inundation of the coastal strip by waves generated by earthquakes or volcanic eruptions in the ocean. Similar floods are common on the shores of Japan and other Pacific islands.

Bottom profile

One of the causes of floods is rising seabeds. Each river gradually accumulates sediments, in riffles, in mouths and deltas.

Flood Prevention Methods

The most effective way to combat river floods is to regulate river flow by creating reservoirs. To combat floods in seashore barrier dams are used.

One of the ways to combat floods is to deepen riffles and other shallows.

History of floods in Russia

Floods in the Krasnodar region

An almost annual natural disaster, the scale of which depends on weather conditions. But the reasons lie in the social sphere, including: the development of the floodplain, water protection zones and littering of the river bed, heavily overgrown in some areas. Catastrophic flood in the Krasnodar region in 2012.

Floods in Moscow

It is known from the history of Moscow that floods on the Moscow River occurred frequently (in the spring, and also happened in the summer) and brought great disasters to the city. Thus, the chronicle speaks of a severe frosty winter, heavy snows and great floods. In July and August, flooding occurred as a result of long, continuous rains. In the 17th century Three spring floods were noted: in , (the southern wall of the Kremlin was damaged, many houses were destroyed) and in (4 floating bridges across the river were demolished). In the 18th century six floods are mentioned: , , , , and ; in 1783, the supports of the Bolshoi Kamenny Bridge were damaged by floods. During the floods in 1788, marks were made on the tower of the Novodevichy Convent and the walls of some buildings. One of the largest floods on the Moscow River was in, during which the maximum water flow was 2860 m³/s. The water in the river rose 8.9 m above the permanent summer horizon; on the embankments near the Kremlin its layer reached 2.3 m. The river and the Vodootvodny Canal merged into one channel 1.5 km wide. 16 km² of the city territory was flooded. During the flood, the maximum flow rate was 2140 m³/s, the water rise above the low-water period was 7.3 m. The next and last flood was in (water rise 6.8 m). Nowadays, in the upper part of the Moscow River basin, Istrinskoye, Mozhaiskoye, Ruzskoye and Ozerninskoye reservoirs have been built, which regulate the flow. In addition, the river bed within the city has been widened in places, sharp bends have been straightened, and the banks are reinforced with granite embankment walls. After this, floods within the city passed almost unnoticed.

Floods often occurred on the river. Yauza during spring floods and heavy summer rains. The modern Elektrozavodskaya, Bolshaya Semyonovskaya, Bakuninskaya streets, Preobrazhenskaya, Rusakovskaya, Rubtsovskaya, Semyonovskaya embankments suffered especially often and severely. An additional reason for flooding on the river. The Yauza was served by the presence of bridges in the form of brick vaulted pipes of insufficient cross-section. Large spring floods were observed in (the water at the Glebovsky Bridge rose by 3.28 m), in (by 2.74 m), in (by 2.04 m), in (by 2.25 m). To replace the old bridges, high reinforced concrete bridges were built, along the banks - reinforced concrete walls (with a margin of 0.5 m above the maximum flood horizon).

Most often Moscow suffered from floods on the river. Neglinnaya after its enclosure in a brick pipe (in the first half of the 19th century in the area from the mouth to Samotyochnaya Square, in - above Samotyochnaya Square). The pipes were designed to carry only 13.7 m³/s of water, and almost every year during heavy rainfalls it burst out of the ground and flooded Samotechnaya and Trubnaya squares and Neglinnaya street. The water on Neglinnaya Street rose by 1.2 m. After a heavy rain, Neglinnaya Street turned into a seething stream. After a rainstorm on June 25, a lake formed at the intersection of Neglinnaya Street and Rakhmanovsky Lane; The flooded area was 25 hectares. Neglinnaya Street, Trubnaya and Samotyochnaya squares were flooded somewhat less, twice - on June 8 and 22, and on August 7 and 9; this happened in . A new pipe has now been laid, designed to carry a water flow of 66.5 m³/s. However, the increasing intensity of rainfall in Moscow again leads to severe floods: on June 26, 2005 in the area of ​​Neglinnaya Street and on June 9, 2006 on Entuziastov Highway, when the first floors of buildings were flooded with water.

Flooding also occurred on the Khapilovka, Rybinka, Presnya and other rivers, which also occurred due to heavy rainfall and insufficient cross-section of pipes (large cross-section pipes are now installed).

Floods in St. Petersburg

Main article: Floods in St. Petersburg

Floods in St. Petersburg are caused by a number of factors: cyclones arising in the Baltic with a predominance of westerly winds cause a surge wave and its movement towards the mouth of the Neva, where the rise of water intensifies due to shallow water and narrowing of the Neva Bay. Seiches, wind surges and other factors also contribute to flooding.

Literature

• // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional ones). - St. Petersburg. , 1890-1907.

Links

	Flood in Wiktionary
	Flood on Wikimedia Commons
	Flood in Wikinews

• Major Flood Database (in English)
• General information and chronology of floods in St. Petersburg on the Neva River

- this is a significant flooding of an area with water as a result of a rise in the water level in a river, reservoir, lake or sea, caused by an abundant influx of water during snowmelt or rainfall, wind surges of water, as well as during congestion, ice jams and other phenomena.

Flooding is dangerous natural phenomenon, a possible source of an emergency if flooding of an area with water causes material damage, harms public health, or leads to the death of people, farm animals and plants.

In terms of frequency, area of ​​distribution and total average annual material damage, floods on the territory of the Russian Federation occupy first place among natural disasters, and in terms of the number of human casualties and specific material damage (per unit of affected area) they take second place after earthquakes.

Rivers are different different conditions formation of water flow (water flow is the amount of water flowing through the final section of the river over any time interval).

According to the conditions for the formation of runoff and the occurrence of floods, the rivers of the Russian Federation are divided into four types (Table 1).

Table 1

Types of rivers of the Russian Federation depending on the conditions for the formation of maximum flow

Formation conditions maximum flow	Areas of distribution on the territory of the Russian Federation
Spring melting of snow on the plains	European part of the Russian Federation and Western Siberia
Melting of mountain snows and glaciers	North Caucasus
Heavy rainfall	Far East and Siberia
Combined influence of snowmelt and precipitation	Northwestern regions of the Russian Federation

The diversity of floods can be reduced to five general groups that unite various floods according to the reasons for their occurrence and the nature of their manifestation (Table 2).

Within the Russian Federation, floods of the first two types predominate (about 70–80% of all cases). They are found on plains, foothills and mountain rivers, in the northern, and southern, western and eastern regions of the country. The remaining three types of floods have a local distribution.

The classification of floods depending on the scale of their distribution and frequency is presented in Table. 3.

Table 2

Types of floods depending on the causes and nature of the manifestation

Types of floods	Causes	Nature of manifestation
High water	Spring melting of snow on the plains or spring-summer melting of snow and rainfall in the mountains	Repeat periodically in the same season. Characterized by a significant and prolonged rise in water levels
Flood	Intense rains and melting snow during winter thaws	There is no clearly defined periodicity. Characterized by an intense and relatively short-term rise in water level
Congestion, gluttony floods (congestion, gluttony)	Great resistance to water flow in certain sections of the river bed, which occurs when ice material accumulates in narrowings or bends of the river during freeze-up (jazzhi) or ice drift (jammies)	Jam floods form in late winter or early spring. They are characterized by a high and relatively short-term rise in the water level in the river. Jam floods form at the beginning of winter and are characterized by a significant (but less than a jam) rise in water level and a longer flood duration
Surge floods (surges)	Wind surges of water in sea estuaries and on windy areas of the coast of seas, large lakes, and reservoirs	Possible at any time of the year. Characterized by a lack of periodicity and a significant rise in water level
Floods (flooding) resulting from dam failures	An outflow of water from a reservoir or reservoir, formed when a pressure front structure (dam, dike, etc.) breaks through or during an emergency release of water from a reservoir, as well as when a natural dam breaks through, created by nature during earthquakes, landslides, landslides, or glacier movement	Characterized by the formation of a breakthrough wave, leading to flooding of large areas and destruction or damage to objects encountered along the path of its movement (buildings, structures, etc.)

Table 3

Classification of floods depending on the scale of distribution and frequency

Classes floods	Scope of distribution floods	Repeatability
Low (small)	Causes relatively minor damage. Covers small coastal areas. Less than 10% of agricultural land is flooded. They hardly disturb the rhythm of life of the population.	5-10 years
High	They cause significant material and moral damage, cover relatively large areas of land in river valleys, and flood approximately 10-15% of agricultural land. They significantly disrupt the economic and everyday life of the population. Lead to partial evacuation of people.	20-25 years
Outstanding	They cause great material damage, covering entire river basins. Approximately 50-70% of agricultural land and some settlements are flooded. Paralyze economic activity and sharply disrupt the everyday life of the population. Lead to the need for mass evacuation of the population and material assets from the flood zone and protection of the most important economic facilities	50-100 years
Catastrophic	They cause enormous material damage and lead to loss of life, covering vast territories within one or more river systems. More than 70% of agricultural land, many settlements, industrial enterprises and utilities are flooded. Economic and production activities are completely paralyzed, the lifestyle of the population is temporarily changed	100-200 years

The main characteristics of water flow are given in table. 4.

During a flood, secondary damage may occur. damaging factors: fires (due to breaks and short circuits of electrical cables and wires); collapse of buildings and structures (under the influence of water flow and due to erosion of the foundation); diseases of humans and farm animals (due to pollution drinking water and food products), etc.

Buildings that periodically fall into a flood zone lose their capital quality: wood is damaged by rot, plaster falls off, bricks fall out, metal structures corrode, due to erosion of the soil under the foundation, uneven settlement of buildings occurs and, as a result, cracks appear.

The main characteristics of the consequences of floods are as follows:

The number of people in a flood-prone area (here we highlight: the number of victims, the number of victims, the number of people left homeless, etc.);
the number of settlements caught in the flood zone (cities, urban settlements, rural settlements that are completely flooded, partially flooded, or caught in the flood zone are distinguished here);
the number of objects in various sectors of the economy caught in the flood zone;
length of railways and highways, power lines, communications and communication lines caught in the flood zone;
number of bridges and tunnels flooded, destroyed or damaged as a result of flooding;
number of residential buildings flooded, destroyed and damaged as a result of flooding;
area of ​​agricultural land affected by flooding;
number of dead farm animals, etc.

Generalized characteristics of the consequences: the amount of damage caused by a flood.

Table 4

Characteristics of the main damaging factor of floods

Basic striking factor	Characteristics of the main damaging factor	Units measurements characteristics
Water flow	Maximum water level during the flood (in the river section under consideration)	m or cm
	Maximum water flow during the flood (in the river section under consideration)	m 3 /s
	Current speed (in the river section under consideration)	m/s
	Flooded area	km 2
	Duration of area flooding	weeks, days, hours
	Repeatability of maximum water level	years, months
	Ensuring maximum water level
	Water temperature during flood	degrees Celsius
	Start time (season) of the flood	month, date
	Rate of rise (intensity of rise) of water level during a flood	m/h, cm/h
	Layer (depth) of flooding of the area at the point in question	m, cm

The main features of the situation that arises during floods are: the destructive nature of the emergency situation, the rapid increase in the parameters of damaging factors, the limited survival time of victims who are under their influence; difficulty of access to victims, the need to use special floating devices for this, as well as difficult weather conditions (heavy rains, ice drift, mudflows, etc.).

The main goal of emergency rescue and other urgent work in flood conditions is to search, provide assistance and rescue people caught in the flood zone, if possible short terms, ensuring their survival in the current situation.

The success of emergency rescue and other urgent work during flood mitigation is achieved by:

Carrying out systematic, advance preparation of control bodies and units of civil defense troops, search and rescue units and services for conducting emergency rescue operations; rapid response to the occurrence of a natural disaster, alerting and deploying the necessary forces and means, organizing effective reconnaissance and deployment of a command and control system;
application effective ways and technologies for searching and rescuing victims, as well as methods for protecting the population and economic facilities;

Rescue operations in conditions of floods and catastrophic flooding include:

Search for victims;
ensuring rescuers' access to victims and rescuing victims;
providing first aid to victims medical care;
evacuation of victims from the danger zone.

Urgent emergency work to eliminate the consequences of floods includes:

Strengthening (construction) of enclosing dams and shafts;
construction of drainage channels;
eliminating congestion and jams;
equipment of berths for life-saving equipment;
protection and restoration of road structures;
restoration of energy supply;
localization of sources of secondary damaging factors.

The main ways to protect people from the damaging factors of floods are the evacuation of the population from flooded areas, the placement of people in non-flooded parts, non-destroyed structures and areas of the terrain.

Depending on the location of a populated area, the time before the start of flooding, the state of transport communications and other factors, evacuation can be carried out immediately before receiving a signal about possible flooding of the area or only in case of an immediate threat of flooding, on foot or using vehicles. In addition to the evacuation of the population, the removal of farm animals, material and cultural assets can also be carried out in an organized manner.

The effectiveness of evacuation as a method of protecting the population during floods depends mainly on timely warning of danger, the degree of preparedness of the population and routes.

For this purpose, in areas of possible flooding, a population warning system is created, information is provided in advance about the location of settlements relative to a possible dangerous zone and evacuation routes, training is conducted with the population and evacuation authorities on practical training on evacuation issues, including people’s independent exit to non-flooded areas .

In addition to the direct impact of water flow, aspiration (entry into the respiratory tract) of water, prolonged exposure to cold water, neuropsychic stress, as well as flooding (destruction) of systems that support the life of the population, especially failure of water supply and sewerage systems.

When people are forced to stay in water with a low temperature for a long time, hypothermia (hypothermia) of the body occurs. If a person gets into water, hypothermia is possible even with relatively high temperature(Table 5).

Accommodation of people in non-flooded parts, non-destructible structures and areas of terrain is used in cases where high speed water flow causes its rapid arrival in populated areas and (or) the population cannot be evacuated to a safe area. In this case, the implementation of such protective measures, as a rule, requires the further implementation of rescue operations to evacuate people from places of temporary accommodation in danger zone. It should be borne in mind that the population can also use the upper parts of trees as a place of temporary stay (shelter).

Table 5

Time of safe stay of a person in water

Water temperature, °C	Safe stay time, min
	420-540
5-15	10-270
	10-15
Up to 2

The decision to carry out rescue and other urgent work during a flood is made on the basis of reconnaissance data, which during floods is organized to identify the situation in disaster areas in order to minimize damage.

Determination of flood boundaries;
monitoring the dynamics of flood development;
identifying the locations of people and farm animals in need of help;
identification of material assets to be removed from the disaster zone;
selection and reconnaissance of evacuation routes for people, animals and material assets by watercraft, equipment of berths;
selection and equipment of helicopter landing sites in the disaster area.

To carry out emergency rescue operations, units of civil defense troops and search and rescue teams (services), reinforced with landing craft, are assigned. To carry out other urgent work, taking into account their nature, engineering, engineering and technical, road units and formations are appointed.

When searching and rescuing victims in water and in flooded areas, aviation technologies using airplanes and helicopters should be widely used.

The use of certain technologies for eliminating ice jams and landslides depends on the scale of floods and the associated consequences. The main method of destroying the ice cover, eliminating ice jams, as well as landslides rocks are explosive. The work is carried out by pyrotechnic units equipped with boats and vehicles equipped for the delivery of explosives and means of detonation. During catastrophic floods, especially on large rivers in the North and Northeast of Russia, flowing from south to north, destruction of ice cover, ice jams and ice jams using bomber aircraft is practiced.

Measures to prevent floods and eliminate their consequences are provided for in action plans for prevention and elimination emergency situations, developed at all levels by emergency commissions.

Organizing the interaction of liquidation forces, the consequences of floods and catastrophic flooding of territories is one of the most important factors ensuring the success of rescue and other emergency operations.

Interaction is organized primarily in the interests of rescue units and the implementation of these works in the shortest possible time.

The experience of recent years in eliminating the catastrophic consequences of floods (Yakutia - 2001, Southern Federal District - 2002) suggests that in order to improve the protection of the population and territories from floods, the executive authorities of the constituent entities of the Russian Federation and local governments can recommend:

Accelerate the formation of territorial monitoring systems, laboratory control and emergency forecasting;
take measures to develop public warning systems, paying attention to special attention rural areas;
take measures to create and strengthen bank protection structures, repair dams, deepen and clean river beds;
intensify efforts to create search and rescue units financed from the budgets of the constituent entities of the Russian Federation;
taking into account this experience, revise action plans for the prevention and response to emergency situations;
create full reserves of financial and material resources to eliminate emergency situations;
consider the need (expediency) of redistributing funds from the budgets of the constituent entities of the Russian Federation in the direction of increasing funds for urgent measures aimed at the safe functioning of the regional water management complexes.

After the Great Flood inundated the entire surface of our planet, floods are considered one of the most dangerous natural disasters in the world. While they may not look as grandiose and impressive as a sudden tornado or typhoon, and often give people time to leave the dangerous area, the consequences of floods are no less dire.

Thus, the largest documented flood in the world occurred in China in the thirties of the last century, when the longest and deep river country, the Yangtze, together with the neighboring Yellow River, overflowed its banks after prolonged rains, destroying dams and flooding more than 300 thousand hectares of fertile land (in some areas the water did not drain for about six months). When the river waters calmed down, the consequences of the flood were so catastrophic that the world shook: according to official data alone, the death toll exceeded 3.7 million people.

A flood is the inundation of large areas, which was caused by a rise in water levels in lakes, rivers, and seas after heavy rainfall, melting snow, and a dam break, which led to water flowing far beyond the boundaries of the coastline.

Despite the fact that in most cases the population can be warned about the approach of a natural disaster, warnings are often ignored due to the fact that local residents refuse to leave their homes in the hope that the disaster will bypass them. And it’s completely in vain: the advancing water spares no one and not only destroys buildings (especially buildings with a shallow foundation and constructed of wood), but often leads to human casualties.

Speaking about the causes of floods, hydrologists identify the following factors:

• Long rains - this type of flood occurs only in humid areas, which are characterized by large number precipitation. For example, numerous showers that often fall in summer time on the Abyssinian Highlands, supplying the Nile with water, lead to the fact that the river annually floods the entire valley of the mouth. Despite the fact that the soil here is ideal for the development agriculture, you cannot delay harvesting, otherwise it will be destroyed by the arriving waters.
• Melting snow - the cause of flooding is the intense melting of the snow cover, when the water entering the ground is quickly directed to nearby rivers, sharply increasing the amount of water in them, as a result of which even a very small river increases in size many times over.
• Tsunamis - floods that bring with them tsunamis most often become catastrophic, often flooding the entire coast and going deep up to four kilometers. A tsunami is formed in the ocean as a result of the shift of lithospheric plates, also huge waves can form in lakes and bays after large landslides fall into them from a height.
• Raising the bottom - over time, any river accumulates sediment in places where it bends, which causes flooding. The depth of the river in these places decreases, but the flow expands, flooding the coastal strip.
• A reservoir breakthrough is an extremely destructive element, since the flow of water that breaks through is extremely strong, and therefore is not inferior in strength to a tsunami: it demolishes everything that is in its path, regardless of the weight of the object.

What are floods like?

Naturally, not all types of floods lead to catastrophic consequences. Those that occur most frequently are not as destructive as those that occur once every few decades, but the effects of such floods are felt over a significant period. Therefore, hydrologists, focusing on the consequences of floods, classified the elements into four groups and gave them a description.

Small floods created by lowland rivers cover small coastal areas, occur once every five to ten years, and the population easily copes with the consequences of floods of this type.

Floods classified as “Dangerous” are much more serious. They happen less frequently, once every 20-25 years. Covering fairly large plots of land located in river valleys, cause significant material damage, flooding from 10 to 20% of crops. In some cases, partial evacuation of the population is even required.

Floods, which hydrologists call “Particularly Dangerous,” occur once every fifty to hundred years. Having overflowed its banks, the river waters completely fill the river basins, destroying from 50 to 70% of crops, and in some cases, populated areas. As a result, all agricultural activity and the life of the region are paralyzed, and the way of life of local residents is sharply disrupted, especially considering the fact that during particularly dangerous floods, mass evacuation of the inhabitants of a dangerous area is required.

The most dangerous types of floods in the world are classified as “Catastrophic” (this is the type of flood that befell China in the thirties of the last century). They flood the area of ​​one or more water systems, destroying almost all agricultural land, settlements (including cities), and causing massive loss of life. The country usually copes poorly with the consequences of floods of this scale and requires international assistance, since disasters often cause a humanitarian catastrophe.

In addition to classification according to the consequences of flooding, there are the following types floods, based already on the description of this phenomenon:

1. High water. This type of flood on the plains inundates low-lying areas and occurs in the spring during snowmelt or after rain. Usually refers to small floods, but in some cases, if the soil was very saturated with moisture in the fall and was very frozen in winter, the consequences of the floods can be catastrophic.
2. Flood. A rapid but short-term rise in water levels in rivers is called a leash. This type of flood can occur several times a year, as its occurrence is primarily influenced by heavy rainfall and, in some cases, rapid melting of snow during thaws.
3. Congestion. A jam forms early spring due to blockage of rivers ice block or several ice floes that slow down the river flow and cause water to rise above the ice. Floods of this type are characterized by a high but short rise in the water level in the river.
4. Gluttony. Ice flooding occurs due to an ice plug, which is a concentration of loose ice in narrowing areas of the river. During this flood, the water does not rise as much as during jams, but at the same time, this flood lasts longer.
5. Wind surge. This flood is characterized by a large rise in water and is caused by wind. Since air flows need to properly disperse the wave to do this, the wind surge is usually fixed at sea ​​coast, at the mouth of the river, on big lakes, reservoirs. Predicting this flood is not easy, since it is characterized by a lack of periodicity and short duration.
6. Break in the reservoir. Floods of this type are formed due to the failure of a reservoir, dam, or dam. Despite their short duration, these floods are dangerous due to their suddenness and unpredictability, as a result of which a significant area is under water, and many objects that are in the path of the water are destroyed.

What to do in case of floods

To reduce the risk of occurrence and minimize the consequences of floods, flood protection is created in reservoirs - shallows are poured, riffles are deepened, and to regulate river flow, protective dams are built on the seashore, and reservoirs are built on rivers that level out the flow of the river flow, increasing it in summer and decreasing it in the spring.

Unlike other natural disasters, scientists predict the likelihood of a flood quite accurately (unless, of course, they are the result of events that are not easy to predict, such as a tsunami or a dam failure). Once warned of an impending disaster, people have time to put in place the necessary flood protection.

If a catastrophe of enormous proportions is coming, special services they begin to evacuate the population (however, these actions are not always successful, since many refuse to leave their homes).

People living in areas prone to floods must know the rules of behavior during floods in order to correctly calculate their actions in emergency situations. To do this, it is necessary to study in advance the boundaries of possible flooding, and also take into account all the hills and places that will be least affected by the elements, and where it will be possible to wait out the flood. It is also worth finding out in advance where boats, rafts or building materials so that in case of disaster they can be made into a floating craft.

The danger zone should be left as soon as information about flooding appears. It is also worth taking with you a pre-prepared backpack with documents, medicines, valuables, warm clothes and a two-day supply of food. Before leaving the house, you need to turn off the electricity, turn off the gas, extinguish the fire in the stoves, it is advisable to secure light objects outside the room so that they do not float away. Window and door openings should be locked, and if possible, the outside should be covered with boards or shields.

If you can’t leave the house, you need to get out onto the roof and attach a banner so that rescuers know where to look for you. If it is night outside, you need to signal your location with a torch or flashlight. When rescuers approach, you need to calmly, without sudden movements, get into the rescue boat, and then listen to their instructions.

If there is no help, and the water remains and threatens to flood the shelter, you need to take a raft or object that can be used instead of a floating device and swim in the right direction, not forgetting to send distress signals. If people are found in the water along the way, everything must be done to save them. To do this, you need to calm the drowning person down and then throw him a rope. If a person is in a state of panic and does not understand anything, you need to swim up to him from behind and tow him by the hair so that he cannot drown the rescuer.

Returning after a flood, before going home, you need to make sure that the building is strong and will not collapse, and then ventilate the room. Before turning on electrical appliances, or even lighting a match, be sure to check the gas pipeline, electrical wiring, as well as water supply and sewerage for serviceability (it is advisable to do these actions with specialists). After making sure that everything is in order, you need to pump out water from the basements, dry the rooms, and clean the wells of dirt.