| Origin and types of floods. Their consequences

Basics of life safety
7th grade

Lesson 16
Origin and types of floods. Their consequences

FROM THE HISTORY OF FLOODS

Less than four months had passed since the founding of St. Petersburg when a flood occurred. On the night of August 30-31, 1703, the water in the Neva rose by more than 2 m and flooded the camp of the Russian troops. Food warehouses were flooded, and part of the forest prepared for the construction of the Peter and Paul Fortress was destroyed.

The head of the garrison, A.I. Repnin, reported to Peter I: “It’s great, sir, our weather from the sea is cruel, and in our place where I stand with the regiments, water is pouring right up to my camp, sleeping in the Preobrazhensky regiment at midnight taverns of many sleepy people and their junk was wet..."

Two years later, on the night of October 15-16, the same warehouses were flooded again. Under the pressure of furious waves and hurricane winds, the walls of houses collapsed, roofs fell off, and uprooted trees fell.

An eyewitness to the flood, writer A.P. Baschitsky wrote: “ Winter Palace like a rock, standing in the middle of a stormy sea, it withstood the onslaught of waves from all sides, crashing with a roar against its strong walls and watering them with splashes almost to the top floor. On the Neva, the water boiled as if in a cauldron, and with incredible force reversed the flow of the river..." 

The flood of September 21, 1777 took the city by surprise in the dark autumn night. A fierce storm and extremely rapid rise of water greatly aggravated the situation. Due to the disorganization of the population and the lack of management of the authorities, the flood of 1777, despite its short duration, caused enormous damage to the city. Many fences and fences were overturned, wooden houses were knocked down. The water washed away the prison, which was located on the seashore, along with 300 prisoners. The fountains in the Summer Garden were destroyed (they were never restored).

Catherine II in her diaries described the storm on that memorable night: “From that moment, everything flew in the air, tiles, iron sheets, glass, water, hail, snow... On the embankment, which is not yet finished, three-masted merchant ships. The exchange has changed its location... My cellars are flooded with water, and God knows what will happen to them.”

The flood of 1824 brought huge losses to the city. 208 people died (according to other sources - 569 people). The Neva remained turbulent until the middle of the winter of 1824/25. 324 houses were completely destroyed, 3257 various other buildings were damaged (i.e., half of all existing ones). Of the 94 ships docked in the harbor, only 12 were saved. 3,600 heads of livestock drowned, 900 thousand pounds of flour and large number other food. For a long time after this flood, colds were rampant in the city. Prices for food and firewood have skyrocketed. For more than half a century, this flood was called the “flood.”

Origin and types of floods

Flood is a significant inundation of water in an area adjacent to a river, lake, sea or reservoir, which damages the health of people or even leads to their death, and also causes material damage.

From 1900 to 2006, there were 2,855 major floods worldwide. 7 million people died in them.

Depending on the scale, frequency and damage caused, floods are classified as low, high, outstanding and catastrophic.

Low (small) floods occur mainly on lowland rivers. At the same time, water floods low-lying areas (less than 10% of agricultural land). Such floods hardly disrupt the rhythm of life of the population and cause minor damage. They repeat once every 5-10 years.

High floods significantly disrupt people's normal lives and cause significant material damage. In densely populated areas, there is often a need for partial evacuation of the population. Such floods occur once every 20-25 years.

Outstanding Floods cover entire river basins. They cause great material damage and flood settlements and cities. This creates the need for mass evacuation of people and material assets. Occurs once every 50-100 years.

Catastrophic floods completely change the way of life of the population and lead to huge material losses. More than 70% of agricultural land is flooded. Such floods occur no more than once every 150-200 years.

Floods rank first in the world in terms of the number of natural disasters they cause and the second or third place in the number of victims.

Let's turn to the history of our country. The Ipatiev Chronicle recorded a terrible flood in the south of Russia in 1145, which was caused by heavy rains... Another chronicle (Troitskaya) says that in 1403 due to heavy rains floods were observed from Pskov to Paris.

Depending on the causes, floods are divided into several types.

Floods are floods caused by spring melting of snow on the plains or melting of snow and glaciers in the mountains. They are repeated annually in the same season with varying intensities and durations, which depend on meteorological conditions. Floods are characterized by a significant and prolonged rise in water levels.

Floods are floods caused by rain and downpours or rapid melting of snow during winter thaws. An intense but relatively short-term rise in water level is characteristic. Unlike floods, floods occur at any time of the year.

Jam, jam floods (jams, jams) - floods caused by high resistance to water flow that occurs when ice material accumulates in narrowings or bends of the river during freeze-up (jags) or during ice drift (jams).

Jam floods formed at the end of winter or spring. They are characterized by a high and relatively short-term rise in the water level in the river.

Zazhornye floods are formed at the beginning of winter. They are characterized by a significant, but less than a jam, rise in the water level and a longer duration.

On medium-sized rivers, the total length of the jam can be from one to several kilometers. The length of the watershed section can reach up to 20 km on large rivers. Ice jams most often occur on rivers flowing from south to north. In Russia, these are the Northern Dvina, Pechora, Yenisei, Ob, Lena, Irtysh, Vitim, Tom, etc. Icebreakers are used to break up congestion, blasting operations and bombing from aircraft are carried out.

Surge floods are caused by wind surges of water onto the shores of large lakes, reservoirs and into the sea mouths of large rivers. They arise on the windward shore of a reservoir as a result of a rise in water level under the influence of a strong cyclone wind on the water surface. In this case, a surge wave is formed, propagating to the windward shore of the reservoir or up the river. Surge floods are characterized by a lack of periodicity and a significant rise in water levels. The surge wave can spread to large rivers for hundreds of kilometers, for small ones - for tens of kilometers. Flooding usually lasts from several tens of hours to several days.

Of the world's 200 capitals, about half are located in estuaries and are threatened by surge floods. In Russia, St. Petersburg, located in the river delta, is most susceptible to this phenomenon. Neva on low islands. Since its foundation (1703) it has been attacked by waves about 250 times.

Floods caused by the failure of dams (hydraulic structures). They occur when water overflows over the crest of a dam due to untimely pre-flood drainage of the reservoir, when the dam is destroyed or the dam's spillway capacity is insufficient. Dam failure is also possible due to poor quality of construction work and improper operation, the impact of earthquakes and the consequences of military operations. Such floods are characterized by the formation of a breakthrough wave, leading to the flooding of large areas and to the destruction or damage of objects (buildings, structures) encountered along the path of its movement.

Floods caused by underwater earthquakes, eruptions of underwater or island volcanoes occur relatively rarely. They occur on the coasts of seas and oceans in areas of active seismic activity.

The classification of floods by scale and causes of occurrence is shown in Diagram 17.

Consequences of floods

During a flood, water quickly rises and floods the surrounding area.

Flooding is the covering of the surrounding area with a layer of water, flooding courtyards, streets of populated areas and the lower floors of buildings.

Flooding is the penetration of water into the basements of buildings through the sewer network (when the sewer is connected to the river), through various kinds of ditches and trenches, as well as due to significant backwater of groundwater.

Flooding of populated areas, agricultural lands and natural complexes is accompanied by negative consequences: as a result of exposure to water and its rapid flow, people, farm and wild animals die; buildings, structures, communications are destroyed or damaged; material and cultural values; agricultural activities are interrupted; crops perish, fertile soils are washed away or flooded; the landscape changes.

Secondary consequences of floods: reduction in the strength of structures as a result of erosion and undermining; transfer of water spilled from damaged storage facilities harmful substances and their pollution of vast territories; complication of the sanitary and epidemiological situation; swamping of the area.

Due to uneven subsidence of the soil during a flood, numerous ruptures of sewer and water pipes, gas lines, electrical, telegraph and telephone cables occur, damage to buildings and roads.

The population endures summer floods and its consequences more easily than spring floods, and even more so winter ones.

In rural areas, the timing (season) and duration of flooding are critical. This is primarily due to the seasonality of agricultural work. But any flooding of areas intended for growing crops with water leads to the displacement of air from the soil. At the same time, normal gas exchange in the soil stops and carbon dioxide enters the water from the roots of the plants, which has a harmful effect on the plants. This circumstance - main reason falling yields or loss of crops due to floods.

Serious consequences of rare floods are sometimes changes in river channels: new channels appear or old ones deepen. Partially, and sometimes completely, washed away or covered with fertile silt top layer soils in plowed areas of the floodplain, which significantly worsens land use and reduces productivity.

Measures to reduce flood damage

It is almost impossible to get rid of floods completely, but people have the power to reduce losses from them.

To protect against most floods, the same measures are used to significantly reduce their consequences: they plant shelterbelts in river basins, try to preserve coastal shrub vegetation, carry out special treatment of slopes, build ponds and reservoirs to intercept melt and rainwater.

On medium and large rivers, a radical means of flood protection is used - regulating flood flow with the help of reservoirs (this simultaneously allows solving the problem of generating electricity). The essence of this method is that the water arriving in the reservoirs is gradually consumed by discharging it through a pressure hydraulic unit.

To protect against floods, dikes are built along the banks of many rivers. Straightening of the channels of winding rivers is also carried out, which makes it possible to increase the slope of the water surface and the speed of water flow. As a result, maximum water consumption occurs at a lower level. On newly built-up areas, the method of filling the territory is used.

Work to strengthen river banks reduces the risk of erosion, and to deepen the river bottom allows a larger volume of water to pass through their beds, remove various obstacles from the bottom, and increase the flow speed.

To carry out operational preventive measures (warning the population about the threat of flooding; early evacuation of the population, material assets, animals from potentially flooded areas; construction of simple protective structures to protect populated areas and roads from flooding), a timely and reliable hydrometeorological forecast is important.

Most floods can be predicted and, as a result, possible losses can be reduced. Residents of cities and towns that periodically fall into flood zones must be informed in advance about this danger, trained and prepared to act in the event of a threat and during floods.

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 formed during earthquakes or volcanic eruptions in the ocean (see Tsunami). Similar floods are not uncommon on the shores of Japan and other Pacific islands. 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 of large areas 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 and some populated areas are flooded. Paralyze economic activity and sharply disrupt the everyday life of the population. They lead to the need for mass evacuation of the population and material assets from the flood zone and the 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 is flooded, many settlements, industrial enterprises and engineering communications. The economic and production activity, the lifestyle of the population changes temporarily. 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.

The congestion occurs due to the non-simultaneous opening of large 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 shore large lakes, reservoirs and seas.
• Flood due to a breakthrough in hydraulic structures ( hydrodynamic accident) is an incident associated with the failure (destruction) of a hydraulic structure or its parts, followed by the 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 downstream.

Snow melting

Intensive snow melting, 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 the littering of the river bed, which is heavily overgrown in some areas. Catastrophic flood in the Krasnodar region in 2012.

Floods in Moscow

From the history of Moscow it is known that floods on the Moscow River often occurred (in the spring, they also happened in summer time) and brought great disaster 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 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

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

According to the Russian Ministry of Emergency Situations, floods rank first in Russia among known natural disasters in terms of frequency, area of ​​distribution, and total average annual damage. 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. The flow of water 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. Flood of lowland rivers in places with temperate climate caused by spring snowmelt (spring flood). Floods on rivers originating high in the mountains are caused by the melting of snow and glaciers in the summer (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, provide examples of floods in the Russian Federation that occurred during 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.

Types of flood	Reasons	Charactermanifestations
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. Significant and prolonged rise in water levels
	Intense rains and melting snow during winter thaws	There is no clearly defined periodicity. Intense and relatively short-term rise in water level
Congestion, gluttony (congestion, gluttony)	Great resistance to water flow, formed 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 during ice drift (jams)	Mash - at the end of winter or spring. A high and relatively short-term rise in the water level in the river. Gluttonous - at the beginning of winter. Significant (no less than during a jam) rise in the water level and a longer duration compared to jams
Surge	Wind surges of water in sea estuaries and windward areas of the coast of seas, large lakes, and reservoirs	Any time of the year. Lack of periodicity and significant rise in water level
Flooding due to dam failure	An outflow of water from a reservoir or reservoir, resulting from a breakthrough of pressure front structures (dams, dikes, etc.), during an emergency release of water from a reservoir, during a breakthrough of a natural dam created by nature during earthquakes, landslides, landslides, and glacier movement	Formation of a breakthrough wave, leading to flooding of large areas and to destruction or damage to objects encountered along the way (buildings and structures, etc.)

On the territory of 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.

Factors influencing the maximum rise in water level during various types of floods are given in Table. 2.2.

Table 2.2

Factors influencing the extent of flooding

Type of flood	Factors influencing the value maximum rise in water levels
High water	The reserve of water in the snow cover before the onset of spring melting; atmospheric precipitation during snowmelt and flood periods; autumn-winter soil moisture by the beginning of spring snowmelt; ice crust on the soil; snowmelt intensity; combination of flood waves of large tributaries of the river basin; lacustrine, swampy and forested areas of the basin; relief of the pool
	The amount of precipitation, its intensity, duration, coverage area, previous precipitation, soil moisture and permeability, basin topography, river slopes, presence and depth of permafrost
Congestion, glutton	Surface speed of water flow, the presence in the channel of narrowings, bends, shoals, sharp turns, islands and other channel obstacles, air temperature during freeze-up (in case of a jam) or during ice drift (in case of a jam), terrain
	Wind speed, direction and duration, coincidence in time with high tide or low tide, slope of the water surface and river depth, distance from the sea coast, average depth and configuration of the reservoir, terrain
Flooding due to dam failures	The magnitude of the water level drop at the dam site: the volume filled with water in the reservoir at the time of the breakthrough; slope of the reservoir and river bottom; size and time of formation of the hole; distance from the dam, terrain

According to the initial causes, floods are divided into surges, storm (rain), floods (associated with the melting of snow and glaciers), gluttonous and mash-filled, obstructive and breakthrough.

Floods passing along rivers are divided by height:

♦ low or small (low floodplains are flooded);

♦ medium (high floodplains, partially populated, are flooded);

♦ strong, or outstanding (cities and communications are partially flooded, evacuation of the population is required);

♦ catastrophic (cities are significantly flooded, major rescue operations, mass evacuation are required).

Floods (not counting surges that accompany hurricanes) rank first in the world in the number of emergencies they create (about 40% of all emergencies), and second or third in the number of victims (7.5 thousand per year in 1947-1970). ), place in the top three in terms of long-term average and maximum one-time magnitude of direct economic damage.

Various legends about the global flood are associated with floods of surge, storm and dammed-outburst nature in the populated areas of southern Asia, Central and South America, behind which are hidden actual events that determined the fate of entire ethnic groups.

Surge floods occur in coastal areas during the passage of deep cyclones, especially hurricanes (typhoons).

Surge water is a rise in its level caused by the influence of wind on the water surface. Surges leading to floods occur at the mouths of large rivers, as well as on large lakes and reservoirs.

The surge occurs on the windward shore of the reservoir due to shear stress at the water-air interface. The surface layers of water, drawn by the wind towards the windward coast, experience only the resistance of the lower layers of water. With the formation of a slope of the water surface under the influence of gravity, the lower layers begin to move in opposite direction, already experiencing much greater resistance to bottom roughness. Due to the inequality of water flows moving in opposite directions, a rise in level occurs at the windward shore of the reservoir and a decline at the leeward shore.

Wind surge just like flood, flood, jam, ice jam, is an extraordinary, especially dangerous hydrological phenomenon. The main condition for the occurrence of surge floods is strong and prolonged wind.

The main characteristic by which the magnitude of the surge can be judged is the surge rise in water level, usually measured in meters.

Other quantities characterizing the surge are the depth of propagation of the surge wave, the area and duration of flooding.

The magnitude of the surge level in sea estuaries is influenced by wind speed and direction. For each area subject to surge floods, it is possible to determine the direction of the wind over the reservoir at which surge phenomena will be maximum.

A common feature of marine estuaries is that the surge may coincide in time with high or low tide; accordingly, it will be either slightly larger or smaller. The surge wave travels further up the river, the lower the slope and the greater the depth of the river. The duration of flooding usually ranges from several hours to several days.

The magnitude of the rise in the surge water level of large reservoirs is influenced by: wind speed and direction; length of wind acceleration over a body of water; average depth of the reservoir along the length of the acceleration; size and configuration of the reservoir.

The larger the body of water, the shallower its depth, the closer its configuration to a circle or ellipse, the large sizes surges and surges of water reach.

The main characteristics of the consequences of surge floods are almost the same as those of flash floods.

In emergency situations associated with mid-latitude and tropical hurricanes (strong winds, heavy precipitation, snow drifts, surge floods (accompanied by hurricanes), sea storms, outbreaks of seashore abrasion, soil salinization in flooded areas), the main threat is floods. They account for 90% of the victims and the lion's share of economic losses.

Surge floods (Japanese - takashio) are caused by: pressure rise in sea level (usually up to 1 m, rarely up to 2.5 m); long waves due to the surge itself (height up to 8-12m); wind short waves. As a result, the water level may rise above normal for a long time: by 4-5 m on the Okhotsk coast; at 6-8 m on the Atlantic coast of North America; at 8-10 m in Japan, the Philippines, Hawaiian Islands; at 11-12 m in the Ganges delta, Bangladesh, at 12-13 m in Australia.

In Russia, the main threat in the Far East is caused by extreme precipitation, snow drifts, and flash floods, the zone of which extends to the Baikal region.

Flash floods– the most common type of flood. They are possible everywhere (even in deserts), except for the Arctic and Antarctic, but are most frequent and strong in areas with a monsoon climate - between 40° N. w. and 40° S. w.

Flash floods are created by heavy rainfall and vary in nature depending on weather and runoff conditions. A particularly sharp (up to a hundredfold) increase in maximum flow rates relative to the average annual flow occurs in arid regions (since the average annual flow rate is small) and in areas with low water absorption capacity of soils - in mountains with a large proportion of rocky surfaces, in areas of permafrost, in paved cities. A particularly rapid increase in costs occurs during relatively short thunderstorms, when the monthly norm of precipitation is poured out in a few hours. But they cover relatively small watersheds (area up to 1000 km2) and are mainly dangerous for cities.

Floods caused by prolonged intense frontal rains are more common. The “record” for the number of victims from such floods belongs to China, where a monsoon climate and flat, flat terrain are combined, and some of the rivers in the lower reaches flow along a bed raised above the developed floodplain, for example, the bed of the river. The Yellow River is elevated to a height of 12–15 m, although the level rise in it can reach 30 m. Catastrophic floods in China occur on average once every 50 years. They are intensified by the breaking of dams protecting rivers, threatening the lives of tens of millions of people, hundreds of thousands of square kilometers of territory, thousands of settlements, and last for 2–4 months. The 1959 flood set a world “record” for the number of victims - 2 million people.

In the United States, 6% of the country's area is prone to floods. Among emergency situations they rank fifth in terms of the number of victims (in 1913–1986 - an average of 130 per year) and first in terms of direct economic damage. At the same time, 70% of the damage occurs from long-term floods, and 80% of casualties occur from short-term, rapidly developing flash floods. Floods that occur when rain coincides with prolonged flooding are especially dangerous. In this case, the water level in the upper reaches of the river. The Missouri-Mississippi could rise to 17 m and flooding would become outstanding or catastrophic.

In countries Western Europe zones of probable flooding during catastrophic floods occupy up to 4% of the territory, 1–4% of the population live in them. In the 80s, severe flash floods were observed in Portugal, Spain, France, Belgium, Great Britain, Germany, Switzerland, Austria and other countries. Settlements, roads, power lines, and agricultural land were damaged.

In Russia, flash floods are most frequent in the Far East with its monsoon climate and further west to the Chita region, where the influence of Pacific cyclones reaches, as well as in Ukraine, the North Caucasus and Transcaucasia. R level The Amur and other rivers in the Far East can rise by 10 m or more. Crops, pastures, and livestock are dying, roads, power lines, populated areas are damaged, and enterprises are shut down. In July 1990, during a typhoon in Primorye, more than two months of precipitation fell. At the beginning of July 1991, a catastrophic flood in Moldova was caused by heavy rains (three monthly precipitation norms) and the failure of dams in ponds and small reservoirs. The height of the breakthrough wave reached 12.5 m, the storm rise of water in the rivers was more than 3.5 m. More than 3 thousand houses, 18 bridges, etc. were damaged and destroyed.

Floods and floods snow melts are common in areas where there is snow cover on approximately 1/3 of the land area. They are most common in Eurasia and North America– on plains and in mountain-glacial areas. On the plains, floods last 15–20 days on small rivers and up to 2–3 months on large rivers, in the mountains - all summer. Floods – peak floods – last up to 15–35 days. In the northern part temperate zone and in inland areas where heavy rainfall is relatively rare, snowmelt floods can be a major cause of flooding.

In Russia, strong (outstanding) floods of this type occur on average once every 10–25 years. They are possible with a combination of abundant autumn soil moisture and rapid snow melting (tens of millimeters of water layer per day), provided by the arrival of masses of warm air with rain. In this case, the amount of snow must correspond to the amount of incoming heat so that lakes of melt water can appear in the snow cover, breaking through under the influence of rain. Snow-water flows (snow melt mudflows) occur in ravines and hilly areas. The effects of meltwater breakthrough are difficult to predict.

An example is the flood in Bashkiria in April–May 1990. Rapid snowmelt was accompanied by torrential warm rains, the river level rose 9 m higher than usual (in the Belaya River) and 3 m higher than predicted. More than 130 settlements were affected, including the city of Ufa, 90 bridges were destroyed, 100 livestock farms etc. 12 people died. Somewhat later, at the end of May, similar events occurred in Evenkia. Water level in the river Nizhny Tunguska rose by 26 m, the city of Tura and a number of villages were partially flooded.

Zhornye and jam floods occur in foothill and lowland areas of rivers covered with ice. These include most of the rivers of Eurasia and North America north of 35° N. w. Jams are accumulations of slush and broken ice that form in winter, while jams are accumulations of ice floes during spring ice drift. In the territory of the former USSR, on 1,100 rivers, there are more than 2,400 ice jams and ice jams. The thickness of the jammed ice accumulations on the Angara and Amu Darya reaches 10–15 m, the length is 25 km, the reduction in the cross-sectional area of ​​the channel is up to 80%. The duration of the gluttons varies depending on the situation - from several days to the entire winter. The depth of the water sometimes increases 4–5 times compared to the open channel. Despite the low water content of rivers in winter, a flood rise in water level can exceed the flood level, i.e., create a threat of flooding. The water level rise reaches 5–6 m on the Northern Dvina, Western Dvina, and Altai rivers; 6–7 m on the Angara and Yenisei; up to 12 m on the river Naryn. As a result of floods, seasonal river ice is created in many areas of Siberia and the mountains of Central Asia - a hindrance to roads.

Congestion is typical for rivers, the opening of which from ice begins from the upper reaches and occurs mechanically. These are all rivers flowing north, primarily the rivers of Siberia and the north of the European part of Russia. In the lower reaches of the Lena, the length of traffic jams reaches 50–100 km. The duration of congestion is up to 12–15 days. The jammed water rise above the maximum flood level often reaches 4–6 m, with a maximum of up to 10 m on many large rivers of Siberia and Far East, on the Northern Dvina, Pechora, Western Dvina, in the upper reaches of the Dniester. On the territory of Russia, the maximum height of the rise of the jammed water level above the low-water level was noted on the Lower Tunguska in the narrowings of the valley - up to 35–40 m. For the formation of jams, a large amount of ice and a friendly spring flood are required. On large rivers in Siberia, such conditions are observed almost every year; the frequency of jams is 70–100%. The most famous are jam floods on the Northern Dvina near Arkhangelsk (recurrence on average once every 4 years, water level height up to 10 m); on the Ob and its tributaries, where Tobolsk, Kemerovo and other cities are under constant threat; on the Yenisei and its tributaries, where in the 20th century. There were 6 catastrophic and many outstanding floods in Krasnoyarsk, Yeniseisk and other cities.

An ice jam occurs at the beginning of winter during the formation of ice cover. The surface velocity of water flow (more than 0.4 m/s), as well as the air temperature during the freezing period, are of decisive importance in the formation of a ice jam. The formation of jams is facilitated by various channel obstacles: islands, shallows, boulders, sharp turns and narrowings of the channel, areas in the tailwaters of hydroelectric power plants. Accumulations of slush and other loose ice material, formed in these areas as a result of the continuous process of formation of inland ice and destruction of the ice cover, cause constriction of the water section of the river bed, which results in a rise in the water level upstream. The formation of a continuous ice cover at the site of the jam is delayed.

Similar characteristics of ice jam and ice jam floods are observed for the rivers of Canada and Alaska. Less frequent, therefore unexpected and especially dangerous, are floods of this type on the rivers of Western Europe and the USA. In the United States, damage from floods accounts for approximately 1/4 of total flood damage.

Zavalnye andoutburst floods less regular than previous types of floods. They occur mainly in mountainous areas and are associated with landslides and landslides (mainly seismogenic) and glacial movements. There are also breakthroughs in artificial dams.

Since 1910, such events have occurred around the world on average 10–15 times a year (including the destruction of large dams – once every 2–3 years). In 1987, in Tajikistan, for example, the dam of the Sargazon reservoir was broken.

Of the consequences of rubble in the former USSR, the most famous is Lake Sarez, up to 500 m deep, which arose on the river. Murghab in the Pamirs as a result of the earthquake of 1911. In the USA, a similar lake was formed by a seismogenic landslide in the canyon of the river. Madison (Montana) in 1959, but was artificially lowered. With the formation of a dammed lake on the Armenian Highlands, in the upper reaches of the river basin. Tiger, that part of the Flood legend that speaks of Noah's Ark at Mount Ararat.

More or less regular glacier movements are possible in all glacial regions of the world. About 5% of mountain glaciers are classified as pulsating (with an interval of years or decades). When moving, they block watercourses and ensure the accumulation of temporary lakes that break out sooner or later. Long-existing periglacial lakes can also break through if they are dammed by a loose ice-containing moraine ridge. Breakthrough waves pass down the valleys, often taking on the character of mudflows. Floods of this kind occur in mountain valleys on average at least once every 10-20 years, and in each mountainous region as a whole once every 2-5 years.

Over the past 200 years, 35 catastrophic outburst floods have been recorded in the Himalayas.

The fact that floods have intensified is confirmed by the fact that in the 1980s around the world, flash floods and snowmelt floods in many areas broke records for 100 years or during the observation period, and according to calculations, some of them corresponded to a frequency of once every 300–400 years (storm floods in New Zealand, Great Britain, Portugal, the snowmelt flood mentioned above in Bashkiria). Some experts associate this trend with the onset of anthropogenic climate change. But local reasons can be considered undoubted: anthropogenic changes in the geometry of river channels, surface runoff in river basins, winter temperature regime of watercourses, as well as the local field of precipitation and snowmelt. The growth factor in the number of artificial reservoirs and outburst floods is obvious.

Changes in river channels, increasing the height of floods, occur through their unintentional anthropogenic siltation and shallowing, as well as through improper channel straightening works (excessive narrowing and straightening). Changes in the conditions of surface runoff occur when swamps are drained, forests are cleared, plowed, and, in cities, when large impermeable surfaces are created. When draining swamps, the maximum surface runoff increases by 1.5-2.5 times; when clearing forests and plowing - 2–4 times, and in small catchment areas - even more, which contributes to siltation, first of all, of small rivers.

An increase in the area of ​​impervious coatings in cities leads to the same increase in the flow rate of flash floods and to an even greater reduction in the time it takes for the flood wave to “reach”, which sharply increases the maximum costs.

The temperature regime of rivers in temperate, colder zones changes when reservoirs are created: a polynya is constantly maintained at the river outlet from the reservoir in winter, which sharply increases the frequency of ice jams, and in some cases, the height of ice jam levels in comparison with natural ones (on the downstream of the Krasnoyarsk hydroelectric power station - by 2 .5 m or more). On the upper reaches of reservoirs, there is an increase in ice jams and congestion, and in some places an increase in the level of ice jams above the previous maximum level of the spring flood.

Local changes in precipitation and snowmelt fields occur in major cities. They create torches of dusty and warm air above them, which significantly increases the frequency and intensity of thunderstorms, and in general - an increase in precipitation by up to 20% compared to the surrounding area. Pollution of the snow cover near cities changes the snowmelt regime. All these changes are still awaiting quantification.

Preventive measures in case of threat of flooding of populated areas and territories

Flood protection measures are divided into operational (urgent) and technical (preventive).

Operational measures do not generally solve the problem of flood protection and must be carried out in conjunction with technical measures.

Technical measures include advance design and construction of special structures. These include: regulation of flow in the riverbed; drainage of flood waters; regulation of surface flow on spillways; embankment; river channel straightening and dredging; construction of bank protection structures; backfilling of the built-up area; restriction of construction in areas of possible flooding, etc.

The greatest economic effect and reliable protection of floodplain areas from floods can be achieved by combining active protection methods (drainage regulation) with passive methods (embankment, channel dredging, etc.).

The choice of protection methods depends on a number of factors: the hydraulic regime of the watercourse, the terrain, engineering-geological and hydrogeological conditions, the presence of engineering structures in the riverbed and on the floodplain (dams, dikes, bridges, roads, water intakes, etc.), the location of economic facilities subject to flooding.

The main directions of action of executive authorities in the event of a threat of flooding are:

♦ analysis of the situation, identification of sources and possible timing of flooding;

♦ forecasting types (types), timing and scale of possible flooding;

♦ planning and preparation of a set of standard measures to prevent flooding;

♦ planning and preparation for emergency rescue operations in areas of possible flooding.

At the federal level, the Russian Ministry of Emergency Situations, with the active participation of Roshydromet and the Ministry of Natural Resources of Russia, carries out planning and preparation of events on a national scale. At the regional level, regional centers of the Russian Ministry of Emergency Situations plan and prepare activities within their competence. At the level of the region, territory, republic, events are planned and prepared in their territories. At the same time, a large share of responsibility lies with the divisions of the Ministry of Natural Resources of Russia: basin water management departments and its territorial water management bodies. During the period of threat of flooding, the management bodies of the Civil Defense and Emergency Situations of the constituent entities of the Russian Federation operate on high alert.

During the period of threat of spring floods and floods on rivers, flood control commissions must provide for the determination of:

♦ boundaries and dimensions (area) of flood zones, the number of administrative districts, settlements, economic facilities, area of ​​agricultural land, roads, bridges, communication lines and power lines falling into flood and flood zones;

♦ the number of victims, as well as those temporarily resettled from the flood zone;

♦ destroyed (emergency) houses, buildings, etc.;

♦ volumes of pumping water from flooded structures;

♦ number of heads of dead farm animals;

♦ location and size of constructed dams, dams, embankments, fastenings of bank slopes, drainage channels, pits (siphons);

♦ preliminary amount of material damage;

♦ the number of forces and assets involved (personnel, equipment, etc.);

♦ measures to protect the population,

During the preparatory period, an important role is played by analyzing the situation and forecasting possible flooding of populated areas.

Analysis of the situation involves identifying possible causes of the threat of flooding of populated areas, which may include high water and high water, as well as factors contributing to the occurrence of flooding and flooding.

At the same time, possible emergency scenarios are identified in which:

♦ the living conditions of people in the administrative districts of a constituent entity of the Russian Federation are significantly disrupted;

♦ human casualties or damage to the health of a large number of people are possible;

♦ there may be significant material losses;

♦ significant damage to the environment is possible.

Identification of the listed emergency situations associated with flooding of territories is carried out on the basis of:

♦ statistical data on floods and long-term observation data for a given territory;

♦ studying action plans for industrial facilities in the event of an emergency;

own assessments of the territorial management bodies of the RSChS.

Based on the identified factors contributing to the occurrence of emergencies, as well as secondary factors that pose a threat to the population and economic facilities, the following is carried out:

♦ assessment of the probability of an emergency;

♦ assessment of the scale of a possible emergency.

Underscaleshould be understood: number of deaths; number of victims; the amount of material damage; the volume of evacuation measures and protection associated with the evacuation of the population; costs of emergency response and restoration work; indirect losses (short production, costs of benefits, compensation payments, pensions, etc.), etc.

An assessment of the likelihood of occurrence and scale of emergency situations caused by accidents at industrial facilities, life support systems, etc. due to the influence of secondary factors is carried out by the administration of the relevant facilities.

Forecasting and assessing the scale of emergency situations should be carried out taking into account the requirements of laws, other regulations and methods recommended by the Russian Ministry of Emergency Situations.

In the absence of such documents for individual specific cases, the executive authorities of the constituent entities of the Russian Federation will organize research to assess the likelihood of occurrence and assess the scale of emergency situations by the scientific forces of the constituent entity of the Russian Federation.

The results of identifying factors contributing to the occurrence of emergency situations associated with flooding of territories and populated areas serve as the basis for making decisions on the implementation of priority preventive measures.

Based on an analysis of the situation, measures to prevent flooding are planned. Planning is regulated by the Federal Law “On the Protection of the Population and Territories from Natural and Technogenic Emergencies”, regulatory legal acts of state authorities of the constituent entities of the Russian Federation and local governments. In this case, it is advisable to distinguish between subject (target) and operational planning.

Subject (target) planning should include organizational, financial, economic and engineering measures to prevent or reduce the risk of flooding.

Operational planning provides for a set of organizational and technical measures to prepare the population, economic facilities and territories for an emergency situation. These measures should be reflected in plans for the socio-economic development of territories, plans for the development of economic sectors, and economic facilities.

Standard procedure for planning emergency prevention measures,caused by flooding,includes:

♦ identification of organizations and institutions that can be involved in organizing and implementing emergency prevention measures;

♦ development and feasibility study of organizational and engineering measures to prevent or reduce the risk of emergency situations;

♦ development and feasibility study of measures to reduce the severity of the consequences of emergency situations on the population, economic facilities and the environment.

The developed plans are coordinated with interested bodies and organizations, approved by the relevant heads of executive authorities and sent to the implementers. Control over the implementation of plans is carried out by the executive power of the territory through the territorial management bodies of the RSChS.

Let us briefly consider the main measures to reduce the consequences of congestion and gluttons.

Congestion cannot be eliminated; it can only be loosened somewhat or moved to another location. When combating ice jam floods, it is necessary to regulate the flow of ice material.

If the risk was great, a person either refused to use floodplain lands or tried to reduce the danger by building simple protective structures. Sooner or later, these protective measures turned out to be insufficient and the person again faced the need to choose. Human activities leading to floods. Man has struggled with floods throughout his entire existence and for his centuries-old history There have been many such natural disasters.

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Plan:

Introduction…………………………………………………………………………………..3

1. Types and causes of floods………………………………………….4

2. Examples of floods in Russia and the world……………………………..8

3. Problems of floods and safety of hydraulic structures.12

Conclusion…………………………………………………………………………………14

List of references………………………………………………………15

Introduction.

It is well known that the state, development and vital activity of the biosphere and human society are directly dependent on the state water resources, but water does not always play a positive role in the functioning of all living things. Unfortunately, sometimes it becomes a powerful element capable of destroying everything in its path.

For many centuries, humanity, making incredible efforts to protect against floods, cannot succeed in this matter. On the contrary, flood damage continues to increase with each passing century. Catastrophic floods and floods quite often occur on the rivers of our country. Vast areas of agricultural land, towns and cities are flooded. Livestock and crops are dying, transport arteries and bridges, residential buildings and industrial structures are being destroyed. Sometimes people die.

Severe floods occur almost every year. Some arise as a result of the rapid melting of heavy snow that covered vast drainage areas, others due to heavy and prolonged rainfall, and others as a result of surge winds that prevent rivers from flowing into their terminal basins.

Catastrophic river floods are perhaps the most significant natural hazard. For centuries and millennia, people have intuitively assessed the risk of floods - weighed the benefits of developing coastal areas against the potential possible consequences their flooding. If the risk was great, people either refused to use floodplain lands or tried to reduce the danger by building simple protective structures. Sooner or later, these protective measures turned out to be insufficient, and the person again faced the need to choose.

1. Types and causes of floods.

Nowadays, rivers have gained importance as a source of energy, irrigation, industrial water supply, waste water, and also as a place of mass recreation, tourism and sports. A flood is the intense inundation of a large area with water above annual levels, one of the natural disasters. Occurs during floods, floods, and dam and dam breaks.

A flood is a relatively prolonged rise in water levels in rivers; which repeats annually in the same season and is accompanied by a high and prolonged rise of water, usually its exit from the channel onto the floodplain. During floods, structures in river floodplains are damaged, banks are washed away, and sometimes valuable agricultural land is covered with sand. The greatest floods lead to floods, which are considered natural disasters.

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.

Natural causes of flooding include:

A) Spring-summer melting of snow and glaciers in drainage areas. Such floods can be predicted by season, and based on snow reserves - also approximately by height and duration. It should be borne in mind that the correlation between snow reserves and flood height is not that high. With relatively small snow reserves, a friendly spring can lead to a large flood. The condition of the underlying rocks (frozen or not) on which the snow cover is located is also important. And vice versa, with large snow reserves, but not frozen soils and an extended spring, when frosts alternate with thaws, the snow in the catchment areas largely “rots”, preventing runoff.

B) Heavy rains. Here, in the sense of a forecast, we can only talk about a flood season, and in the form of a short-term warning - about calendar dates, approximately - about the duration and height of the expected increase in level. IN climatic conditions In Russia, such rises in level are widespread in the monsoons of the Far East, in the southwest of the European territory of the country, in the Cherno rivers sea ​​coast Caucasus, etc. It should be noted the peculiarity of the Caucasian rivers, high floods on which can be observed at any time of the year. In mountainous mudflow-prone areas, floods may be accompanied by the movement of water erosion products, as well as bottom sediments, along river valleys.

B) Wind surges of water. They appear on the coasts of reservoirs and in the lower reaches of rivers flowing into these reservoirs. In terms of timing, they are not predictable; in some cases, we can talk about seasons when surges are generally observed more often and are of greater height. In general, we can only talk about a probabilistic description of the height and duration of surge water rises, which can vary greatly along different sections of the coast. On the coasts of marginal seas one has to reckon with the combined manifestation of surge and tidal level rises.

D) Congestion. Congestion - clogging of the riverbed by a stationary ice cover and 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 of ice accumulation and above it. Jam floods form at the end of winter or early spring, and arise due to the non-simultaneous opening of large rivers flowing from south to north. The exposed southern sections of the river in its course are being dammed accumulation of ice in the northern regions, which often causes a significant increase in water levels. Jam floods are characterized by a high and relatively short-term rise in the water level in the river.

D) Gluttony. Zazhor - ice plug, accumulation of in-water, loose ice during winter freeze-up in narrowings and bends of the riverbed, causing water to rise in some areas above the level of the main riverbed. Jam floods form at the beginning of winter and are characterized by a significant, but less than jam, rise in the water level and a longer flood duration.

E) Sediment deposition when rivers exit from foothill areas to flat areas with a decrease in flow speed and transport capacity of the flow; At the same time, the channel grows, ending up higher than the surrounding area and from time to time “falling” to the side.

J) Fluctuations in the level of closed reservoirs as a result of disturbances in the water balance under the influence of the variability of its components, as is the case, for example, in the Caspian Sea, where the amplitude of the corresponding long-term level fluctuations exceeds 3 m.

The causes of floods are diverse, and each cause or group of causes has its own type of flood. Below we indicate four groups of types of floods.

1. Floods associated with the passage of very large water flows for a given river. Such floods occur during the period of spring snowmelt, with heavy rainfall and rainfall, in the event of dam failures and dammed lakes breaking out.

2. Floods caused mainly by the great resistance that the water flow encounters in the river. This usually happens at the beginning and end of winter due to jams and ice jams.

3. Floods caused by both the passage of large flows of water and significant resistance to water flow. These include mudflows on mountain rivers and water-snow flows in gullies, ravines and hollows.

4. Floods created by wind surges of water on large lakes and reservoirs, and direct causes are associated with various hydraulic engineering measures and destruction of dams. Indirect - deforestation, drainage of swamps, industrial and residential development, this leads to a change in the hydrological regime of rivers due to an increase in the surface component of runoff. Evapotranspiration is reduced due to the cessation of interception of precipitation by the forest floor and tree crowns. If all forests are removed, the maximum flow can increase to 300%. There is a decrease in infiltration due to the growth of impervious pavements and buildings. The growth of waterproof coatings in urbanized areas increases floods 3 times.

Human activities leading to floods:

1. Restriction of the living cross-section of the flow by roads, dams, bridges, which reduces the throughput of the riverbed and increases the water level.

2. Disruption of the natural flow regime and water levels.

It should be emphasized that in a particular water body, floods are usually caused by several reasons, and therefore, in order to determine the estimated characteristics of possible flooding, a comprehensive analysis should be carried out and a composition of probability distribution laws that are characteristic of individual types of floods should be carried out.

2. Examples of floods in Russia and the world.

Man has struggled with floods throughout his entire existence, and many such natural disasters have occurred over its centuries-old history. In Russia, between 40 and 68 crisis floods occur annually.

Floods with catastrophic consequences in the territory modern Russia over the past 20 years there have been:

In 1994 In Bashkiria, the dam of the Tirlyansk reservoir broke and an abnormal release of 8.6 million cubic meters of water occurred. 29 people died, 786 were left homeless. There were 4 settlements in the flood zone, 85 residential buildings were completely destroyed;

In 1998 near the city of Lensk in Yakutia, two ice jams on the Lena River caused the water to rise by 11 m. 97 thousand people were in the flood zone, 15 died;

In 2001 Lensk was again almost completely flooded due to flooding, which led to the death of 8 people. 5 thousand 162 houses were flooded; in total, over 43 thousand people suffered from the flood in Yakutia;

In 2001 V Irkutsk region Due to heavy rains, a number of rivers overflowed their banks and flooded 7 cities and 13 districts (63 settlements in total). The city of Sayansk was especially affected. 8 people were killed, 300 thousand people were injured, 4 thousand 635 houses were flooded;

In 2001 There was a flood in the Primorsky Territory of the Russian Federation, as a result of which 11 people died and more than 80 thousand were injured. 625 square meters were flooded. kilometers of territory. 7 cities and 7 districts of the region were in the disaster zone, 260 km of roads and 40 bridges were destroyed;

In 2002 As a result of severe flooding in the Southern Federal District of the Russian Federation, 114 people died, of which 59 in the Stavropol Territory, 8 in Karachay-Cherkessia, 36 in the Krasnodar Territory. In total, more than 330 thousand people were affected. 377 settlements were in the flood zone. 8 thousand residential buildings were destroyed, 45 thousand buildings, 350 km of gas pipelines, 406 bridges, 1.7 thousand km of roads, about 6 km of railway tracks, over 1 thousand were damaged. km of power lines, more than 520 km of water supply and 154 water intakes;

In 2002 to the Black Sea coast Krasnodar region A tornado and torrential rains struck. 15 settlements were flooded, including Krymsk, Abrau-Durso, Tuapse. Novorossiysk and the village of Shirokaya Balka suffered the greatest destruction. The disaster claimed the lives of 62 people. Almost 8 thousand residential buildings were damaged;

In 2004 As a result of the flood in the southern regions of Khakassia, 24 settlements (1077 houses in total) were flooded. 9 people died;

In 2010 In the Krasnodar region there was a major flood caused by powerful torrential rains. 30 settlements were flooded in the Tuapse and Apsheron regions and in the Sochi region. 17 people died, 7.5 thousand people were injured. As a result of the natural disaster, almost 1.5 thousand households were destroyed, of which 250 were completely destroyed;

In 2012 year, heavy rains led to the most destructive flood in the entire history of the Krasnodar region. 10 settlements were affected, including the cities of Gelendzhik, Novorossiysk, Krymsk, and the villages of Divnomorskoye, Nizhnebakanskaya, Neberdzhaevskaya and Kabardinka. The main blow of the disaster fell on the Krymsky region and directly on Krymsk. As a result of the flood, 168 people died, of which 153 people were in Krymsk, three in Novorossiysk, 12 in Gelendzhik. 53 thousand people were recognized as affected by the disaster, of which 29 thousand completely lost their property. 7.2 thousand were flooded. residential buildings, of which over 1.65 thousand households were completely destroyed.

Around the world you can note:

December 1999 - Severe flooding in Venezuela was caused by rain that continued for a week. A state of emergency was declared in 5 northwestern states and the Federal Capital District. The death toll, according to Western news agencies, exceeded 10 thousand people;
- February - March 2000 - The largest flood in Mozambique was caused by Cyclone Eline. The disaster destroyed hundreds of thousands of houses, huge areas of farmland and caused the death of more than 700 people. About 2 million people, more than 10% of the country's population, were left homeless as a result of the floods;

March 2000 - In Hungary, heavy rains and melting snow caused one of the worst floods in many years. A state of emergency was declared in the eastern regions of the country. More than 200 thousand hectares of land were under water;

September 2000 - in India, the cause of a natural disaster was prolonged and very heavy monsoon rains, which caused a ten-meter rise in water in the rivers. The death toll in the Indian states of West Bengal and Bihar has reached almost 800. In total, up to 15 million people were affected. About 600 settlements were flooded, crops and food storage facilities were completely destroyed;

October 2000 - an emergency in Vietnam was caused by the worst floods in the country's history. Heavy rains in southern Vietnam continued for more than 2 months. The water level in the Mekong River within the city of Ho Chi Minh City exceeded the permissible level and reached 1.26 m. According to official data, 727 people died as a result of the floods, including 239 children. About 45 thousand families were evacuated;
- August 2002 - heavy rains in the summer in northern and central Europe caused catastrophic flooding in August. 250,000 people were directly affected;

2005 - Hurricane Katrina in the United States causes widespread flooding in Louisiana, Mississippi and Alabama. The levees around New Orleans, Louisiana were breached and the entire city was flooded, causing much of the city's population to be evacuated. 1193 people died;

May 2008 - The Ayeyarwaddy Delta in Myanmar floods due to Cyclone Nargis, the largest cyclone ever recorded in the Bay of Bengal. The United Nations reported that 2.4 million people were affected, with about 146,000 dead or missing;

2008 - Haiti. Four tropical disasters Tropical Storm Fay, Hurricanes Gustav, Hanna and Ike, which occurred within 1 month, caused flooding that led to the death of 425 people, destroyed crops throughout the country, up to 600,000 people require international assistance;

2009 - in the Philippines, after two tropical downpours within a week, mudflows and severe flooding occur. The President declares a national disaster. At least 3 million people were affected and more than 540 people died;

2009 - Samoa Islands. An earthquake in the sea led to the formation of a wave up to 6 m high, which washed away all villages up to 1 km inland on the coast of Samoa, American Samoa and Tonga, on the Pacific Islands, killing more than 189 people;

July August 2010 - About 2,000 people died in Pakistan. The flood caused a mass exodus of spiders: they fled from the flow of water on the trees, entangling their crowns with a thick layer of cobwebs, giving the coastal landscapes an ominous look;

July 2011 January 2012 - Thailand was flooded for six months, entire provinces went under water. The flood claimed the lives of more than 600 people.

3. Problems of floods and safety of hydraulic structures.

Floods are among the most destructive and frequently recurring natural disasters. In the Russian Federation, the area of ​​flood-prone areas is about 400,000 km². An area of ​​about 150,000 km², where more than 7 million hectares of agricultural land is located, is subject to floods with catastrophic consequences. Regions most at risk from flooding include: Krasnodar region, Volgograd, Astrakhan, Amur and Sakhalin regions, Transbaikalia, Stavropol region, Buryatia, Primorsky Krai, Dagestan, Kabardino-Balkaria. Recent years in the south of Russia, in the Primorsky Territory, the Republic of Sakha (Yakutia), there is an increase in floods with catastrophic consequences for the population and economic facilities.

The main reasons for the occurrence and increase in the risk of floods are climate change and the occurrence of abnormal weather phenomena, as a result of ice jams in river beds, intensive development and construction of drainage and flooded areas, insufficient provision of settlements and agricultural lands, and reliable engineering protection. Risk factors are measures to restrict (reduce) the flow of the river, economic development of flood-prone areas in the downstream of hydroelectric facilities, with the placement of residential and economic facilities.

The aggravation of the flood problem in Russia is directly related to the aging of the main production assets water management of the country. As the technical condition of hydraulic structures deteriorates, the risk of their destruction during floods increases. From total number hydraulic structures, over 90% are built from soil and stone-soil materials, for which the service life is about 30 years. However, the share of hydraulic structures with a service life of more than 30 years is about 50%. The fight against floods in the Russian Federation consists mainly of fencing the territory with dams, increasing the capacity of rivers, redistributing flow and other engineering measures.

Reservoirs are important to reduce flood peaks. This is why it is planned to release reservoirs before the onset of floods, but this is not enough. In conditions of increasing anthropogenic pressure, pollution and degradation of land and water sources, and the increasing risk of catastrophic floods, the use of an ecosystem approach to environmental management is of decisive importance. It considers environmental, economic and social resources and their interactions. The problem of flooding and the safety of hydraulic structures is an environmental, socio-economic and technical problem. Along with engineering measures, to solve the problem of floods, it is necessary to analyze factors, the safety of the operation of hydraulic structures and, at the same time, focus on warnings and reductions. negative consequences floods, timely provision of accident-free passage of flood waters, modernization and improvement of the safety of hydraulic structures. The fundamental basis for this is a system analysis of the state of functioning water bodies and hydraulic structures, drainage and flood-prone areas, the causes of the consequences of floods, taking into account natural, social and economic resources.

To prevent crisis situations, it is necessary to improve the unified state management system, which presupposes the presence of the Federal Center, basin, regional, municipal structures and, accordingly, unified information and analytical systems based on monitoring of water bodies and hydraulic structures. The mechanism for implementing measures to solve the problem of floods and the safety of hydraulic structures includes the use of a set of organizational, legislative, regulatory, methodological and socio-economic measures.

Conclusion.

Floods are an inevitable natural phenomenon. The task of humanity is to study the characteristics of floods in as much detail as possible and learn to prevent catastrophic consequences.

From history it is clear that man copes with this problem quite successfully. Hydrological scientists carry out the necessary calculations and forecasts, carry out work aimed at combating floods - agrotechnical, forest reclamation, field protection. However, the accuracy of calculations and the timeliness of the activities carried out leaves much to be desired. This can be corrected by the widespread introduction into practice of new technical means of collecting and processing information about the state of the natural environment.

Man continues to build up the banks of rivers and lakes, actively developing river valleys, storms the mountains. For these reasons, the scope of flood control work is increasing. Floods as a natural disaster are becoming increasingly intolerable. Scientific, engineering and socio-economic feasibility studies for flood protection projects are among the most important tasks of specialists in many fields, primarily hydraulic engineers, hydrologists, ecologists and economists.

In the age of technological progress, floods have claimed millions of lives and caused enormous material damage, which tends to increase.

List of used literature.

1. Federal law“On the protection of the population and territories from natural and man-made emergencies” No. 68-FZ dated December 21, 1994 (as amended on July 21, 2014).

2. Vorobyov Yu.L. Catastrophic floods of the early 21st century: lessons and conclusions. Moscow: Dex-Press, 2003.- 352 p.

3. Oleinik T. F. Great natural disasters: floods, earthquakes, volcanoes, tornadoes. - Rostov-on-Don: Phoenix, - 2006. - 254 p.

4. Chumakov B.N. How to survive natural disasters. Moscow: Eksmo, 2005. - 58 p.

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