All about floods. Dangerous consequences of floods

Report on the topic:

"Flood"

performed by: Armina Sargsyan

Faculty: State Medical University 10th group

Flood- this is a significant flooding of an area as a result of a rise in the water level in a river, lake or sea during snowmelt, rainfall, wind surges, congestion, floods, etc. A special type includes floods caused by wind surges of water into river mouths. Floods lead to the destruction of bridges, roads, buildings, structures, cause significant material damage, and at high speeds of water movement (more than 4 m/s) and high heights of water rise (more than 2 m), they cause the death of people and animals.

The main cause of destruction is the impact on buildings and structures of hydraulic shocks from a mass of water, ice floes floating at high speed, various debris, watercraft, etc. Floods can occur suddenly and last from a few hours to 2-3 weeks.

There are also reasons caused by human activity. In recent centuries, especially in the twentieth century, anthropogenic factors have played an increasingly important role in increasing the frequency and destructive power of floods. Among them, first of all, deforestation should be mentioned (maximum surface runoff increases by 250-300%), irrational management Agriculture. A significant contribution to the increased intensity of floods and high waters was made by: longitudinal plowing of slopes, over-compaction of fields when using heavy equipment, and over-irrigation as a result of violation of irrigation standards. Average flood flows in urbanized areas have approximately tripled due to the growth of impervious covers and development. A significant increase in maximum flow is associated with the economic development of floodplains, which are natural flow regulators. In addition to the above, several reasons should be mentioned that directly lead to the formation of floods: improper implementation of flood protection measures leading to the breaking of embankment dams, destruction of artificial dams, emergency operation of reservoirs and others.

Types of floods

High water - a periodically repeated rather long 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 the harsh winter. Spring rains can also lead to increased flooding, when its peak coincides with the peak of the flood.

Flood - an intense, relatively short-term rise in the water level in the 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.

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 flow are dammed by the accumulation of ice in the northern regions, which often causes a significant increase in the water level. Jam floods are characterized by a high and relatively short-term rise in the water level in the river.

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 duration of the flood.

Wind surge - this is a rise in water level in the sea mouths of large rivers and in windy areas sea ​​coasts, large lakes, reservoirs, caused by the impact of strong winds on the water surface. They are characterized by a lack of periodicity, rarity and significant rise in water level, and, as a rule, short duration. Floods of this type were observed in Leningrad (1824, 1924), the Netherlands (1953). However, this type of flood is very short-lived.

Classification of floods by scale.

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. The frequency of recurrence is 5-10 years, causing minor damage.

Dangerous - cause significant material and moral damage, covering relatively large land 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.

Particularly dangerous - cause great material damage, covering entire river basins. Approximately 50-70% of agricultural land and some populated areas are flooded. They 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. A striking example of this is the flood in Tomsk in 1947.

Catastrophic - 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. At the same time, economic and production activities are completely paralyzed, and the lifestyle of the population is temporarily changed. 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. If the city is located close to a river experiencing flooding, it is not very high place, as a rule, floods it too.

Flood protection measures

1) reducing the maximum water flow by redistributing the flow over time;

2) regulation of flood flow using reservoirs;

3) straightening the river bed:

4) construction of enclosing dams (shafts);

5) carrying out bank protection and dredging works, filling low places;

6) plowing land across slopes and planting shelterbelts in river basins;

7) terracing slopes, preserving tree and shrub vegetation.

Prompt preventive measures include:

1) warning the population about the threat of flooding;

2) early evacuation of the population, farm animals, material and cultural assets from potentially flooded areas;

3) partial restriction or cessation of the functioning of enterprises, organizations, institutions located in areas of possible flooding, protection of material assets.

Before evacuating, to protect their home (apartment) and property, everyone must take the following mandatory actions:

1) turn off water, gas and electricity;

2) extinguish burning heating stoves;

3) move valuable items and belongings to the upper floors of buildings (attics);

4) cover (if necessary) the windows and doors of the first floors of houses with boards or plywood.

When receiving an evacuation warning, you must quickly gather and take with you:

1) personal documents placed in a waterproof bag;

2) money and valuables;

3) medical first aid kit;

4) a set of outerwear and shoes for the season;

5) bed linen and toiletries;

6) three-day supply of food. It is better to put things and food in suitcases (backpacks, bags).

All evacuees must arrive at the evacuation assembly point by a specified time to be registered and sent to a safe area.

Floods

Hydrological dangerous phenomena include; high water levels (floods), rain floods, congestion and fire, the effect of surge winds, etc.

Flood- temporary flooding of a significant part of the land with water as a result of rising water levels in a river, lake or sea.

Depending on the causes, natural floods are divided into:

Floods caused by heavy precipitation or intense melting of snow (glaciers) in its river basin.

Floods resulting from a combination of flood waters and ice drift. Ice drift is often accompanied by jams (a pile of ice in the river bed) or jams (accumulation of inland water ice that forms an ice plug), causing additional rise of water and flooding of new territories. If water breaks through an obstacle, a stormy wave can form, creating a risk of flooding in the area downstream. Jams most often form on rivers that flow from south to north, since the southern sections of the river are freed from ice earlier than the northern ones, and the ice flow, which has begun, encounters an obstacle in its path in the form of freeze-up. Zheri are formed in the pre-frost period and, in the presence of non-freezing sections of the river, during the winter.

Floods caused by wind surges. They are observed on sea coasts and at the mouths of rivers flowing into the sea. The air surge traps water at the mouth, causing its level in the river to rise. Floods of this type were observed in the Neva delta, Holland, England, Germany and other regions of the globe. A classic example of this type of flood is the floods in St. Petersburg (there were more than 300 of them during the existence of the city). The largest floods on the Neva were recorded in 1824 and 1924. In terms of their consequences, they were close to the largest floods and tsunamis.

Flooding. The causes of flooding are rising groundwater levels due to heavy rainfall and faulty drainage systems. One of the reasons for land flooding is hydraulic engineering construction, which can lead to redistribution of river flow and blocking of natural groundwater drainage routes.

A hydrological natural disaster caused by a tsunami is also considered a type of flood, although it has tectonic causes.

Experts believe that people are in danger when the water layer reaches 1 m and the flow speed exceeds 1 m/s. A rise of water of 3 m leads to the destruction of buildings and structures.

In Ukraine, floods are the most common natural disaster.

Catastrophic floods with large material losses, as well as human casualties in last years occur in Transcarpathia, their cause is not only natural factors, but also ill-considered human activities, primarily deforestation.

During a flood, there are four flood zones:

First zone- catastrophic flooding - adjacent directly to hydraulic structures or flood sources. It can reach from 6 to 12 km, and the height of the waves reaches several meters, their speed of propagation is 30 km/h or more. The time it takes for a wave to pass through the zone is up to 30 minutes.

Second zone- fast current zone. The length of the zone is up to 15-20 km, the current speed is 15-20 km/h. Wave travel time -

Third zone- middle flow zone. The length of the zone is 30-50 km. Current speed is 10-15 km/h. The wave travel time is 2-3 hours.

Fourth zone- zone of weak current (spill). Its length depends on the terrain and can be 36-70 km from the hydraulic structure or the starting point natural phenomenon. Current speed is 6-10 km/h.

Floods on rivers based on the height of the water rise, the area of ​​flooding and the amount of damage caused are divided into 4 categories: low (small), high (medium), significant (large) and catastrophic. Low floods repeat every 5-10 years, high - after 20-25 years, significant - after 50-100 years and catastrophic - no more than once every 100-200 years.

In Ukraine, floods of the 1st and 2nd categories (low and high) are possible. In total, there are 22.4 thousand rivers on the territory of Ukraine with a total length of 130 thousand km. The rivers of the Carpathians and Crimea are mountainous, fast-flowing, and predominantly rain-fed. Floods and inundations occur there, of course, during the summer rainy season. Other rivers are of the flat type, predominantly snow-fed. Floods and floods are most often a consequence of spring melting of snow.

Gum- a typical lowland river with high spring floods and low summer and winter low water. The food is mainly snow. Spring runoff is more than 50% of the annual flow. The flood begins in mid-April and reaches its maximum in mid-May. In some rainy years there are autumn floods.

Dnieper-characterized by great unevenness of flow both from year to year (change in annual flow from 24 to 73 billion m3) and within one year. During the spring flood, 60-70%, and in some years - up to 80% of the total annual water flow, passes through. In autumn, the water reserves of the Dnieper can increase several times, so in winter, during the thaw period, floods are observed.

In order to regulate the flow of the Dnieper, reduce the risk of floods and provide water to the Dnieper region, Donbass, Krivoy Rog and Crimea, a scheme for the water and energy use of the Dnieper was developed, which included the construction of six large hydroelectric power stations and reservoirs.

Dniester- the water regime is characterized by a clearly defined spring flood and a large number of floods, which alternate with short periods of low levels throughout the year (except for one to three winter months). Floods occur in the spring as a result of melting snow, in the summer - due to heavy rains, in the winter - during thaws.

Southern Bug has fluctuations in water levels from 1.64 m to 9.4 m. The river is fed by snow, rain and underground runoff. Many dams have been built in the upper and middle reaches. In the area of ​​the mouth, flooding is possible due to the impact of surge winds. Runoff is characterized by significant variability. Spring runoff is 61% of the annual flow, summer - 9%, autumn - 12%, winter - 18%.

Pripyat- the right tributary of the Dnieper, it is characterized by long (more than 4 months) spring floods and low water levels in late summer and early autumn. During spring floods, the river overflows its banks, flooding numerous areas.

Seversky Donets- the largest tributary of the Don is right. The average annual flow is 160 m3 per 1 s. Powered by snow and rain. In Ukraine it flows through the territory of the largest industrial regions (Kharkov, Donbass) and is the main source of their water supply. To provide water to Donbass, the Seversky Donets-Donbass canal was built. To improve water supply in Kharkov, a reservoir with a volume of 400 million m 3 was built.

A significant part of the year is regulated by dams, the destruction of which can lead to catastrophic flooding.

Probable zones of possible floods in Ukraine:

- in the northern region- basins of the Pripyat and Desna rivers and their tributaries. Flood area only in the river basin. Pripyat can reach 600-800 thousand hectares;

- in the western region- basins of the upper Dniester (area can reach 100-130 thousand hectares), Tisa, Prut, Western Bug (area possible flooding 20 - 25 thousand hectares) and their tributaries;

- in the eastern region- basins of the Seversky Donets with its tributaries, the rivers Psla, Vorskla, Sula and other tributaries of the Dnieper;

- in the southern and southwestern regions- basins of tributaries of the Lower Danube, the Southern Bug River and its tributaries.

The duration of floods (flooding) can reach 7-20 days or more. In this case, it is possible to flood not only 10-70% of agricultural land, but also a large number of man-made hazardous objects.

Floods were often accompanied mudflows and landslides, destruction of residential buildings, protective dams, bridges, roads and human casualties.

Protecting people in flood conditions includes warning, evacuation of people and other measures in accordance with flood control and population protection plans.

In order to prevent floods, reservoirs are created to regulate river flow, and special protective structures (dams) are built. Thus, a network of reservoirs has been created on the Dnieper River, which makes it possible to systematically regulate river flow and significantly reduce the scale of floods. For example, in Russia, in the Neva delta, a protective complex more than 25 km long is being built, which will close the water area and become a protection against floods.

To ensure protection during floods, civil defense forces and the population are trained.

Personal safety. When you hear a warning about the threat of flooding, turn off the gas and electricity and immediately go to a safe place - to increase. If the flood spreads slowly and you have time, take measures to save property and material assets: move them to a safe place, and occupy the upper floors (attics) and roofs of buildings. Stock up on food and drinking water. Use existing flotation devices or make them from logs, boards, inner tubes and other items.

Once in the water, take off your heavy clothes (woolen clothes can retain heat in water, so it is not recommended to take them off in cold water) and shoes, use objects floating nearby or raised above the water and wait for help.

Actions during floods in enterprises. When there is a threat of flooding, enterprises, if necessary, stop the work of some units, workshops, departments, and in some cases the entire enterprise. IN educational institutions and children's institutions are suspending classes. In departments that have temporarily stopped working, electricity is cut off and the supply of steam, gas, and water is stopped.

24-hour duty of responsible officials and emergency technical service specialists is organized at the facilities.

To protect populated areas, utility buildings, and industrial premises from flooding, the simplest protective hydraulic structures are built: earthen embankments, dams, and dams. In addition, it is necessary to organize surveillance of such structures. Near them, in case of water leakage, emergency materials are placed to close breaks and to build up dams.

The size of human and material losses during a flood depends on the nature and scale of the flood, the population density in the flooded area, the distance of populated areas from the source of the flood, the nature of the development, the cost of material assets located in the flooded area, the presence of protective structures, environmentally hazardous objects, and the seasons. and days, etc.

Important conditions for effective rescue work during a flood are forecasting the possible time of occurrence and scale of floods, timely notification of the population and its evacuation, organizing a search for people in the flooded area, the accuracy of rescue operations, the number of rescue teams, their provision with special means and equipment and preparedness personnel of these formations, timeliness and quality of provision medical care victims, organizing clear interaction between health authorities, rescue and other forces involved in eliminating the consequences of the flood and providing first aid to victims.

In conditions big city in the event of a catastrophic flood, the proportion of the affected population that needs emergency medical care (as a percentage of the population) will fluctuate during the warm period of the year during the day from 0.02% to 2.7%, at night - from 0.06% to 4 ,5%; in the cold season - from 0.04% to 4.3% during the day and up to 0.08% -5.7% at night.

In the event of an immediate threat of flooding, by decision of the head of the civil defense district (facility), the control point is put on alert, where responsible officials are organized and the tasks of the headquarters, services and civil defense formations are clarified.

If there is a threat of flooding, an urgent evacuation of the population and material assets is organized. The population is informed of the locations of the deployment of prefabricated evacuation points, the timing of arrival at the points, and evacuation routes.

The search for people in the flooded area and evacuation are carried out by civil defense units, the population and, if possible, military units. For this purpose, all watercraft are used (bots, barges, boats, boats), etc., you can use improvised means (logs, boards, barrels) and build rafts; it is also allowed to transport people in a designated ford with a depth of no more than 1 m.

After the water has subsided, they begin to eliminate the consequences of flooding. These works include: removing water from flooded areas and draining them; filling up and cleaning dilapidated structures that cannot be restored; pumping water from basements and other premises; repair of water-damaged buildings, utility networks, roads, bridges and other structures; cleaning of flooded areas, agricultural lands, lands, areas of livestock farms, rural streets, courtyards, etc.

Engineering flood protection provides for the construction of small and large reservoirs, which makes it possible to regulate river flow and thus reduce the risk of floods during flood periods.

The problem of flood control requires a long-term forecast.

Floods are significant inundations of an area resulting from rising water levels in a river, reservoir or lake. Floods are caused by heavy rainfall, intense snow melting, and the breach or destruction of dams and dams. Floods are accompanied by loss of life and significant material damage.

In terms of frequency and area of ​​distribution, floods rank first among natural disasters; in terms of the number of human casualties and material damage, floods rank second after earthquakes. It is not possible to completely prevent them either in the present or in the near future. Floods can only be mitigated or localized.

If there is a threat of flooding, preventive measures are taken. First of all, this is informing the population about the threat of flooding, strengthening monitoring of water levels, and alerting the forces and means intended to combat the disaster and evacuate the population. The condition of dams, dams, bridges is checked and identified deficiencies are eliminated. Additional embankments are being erected, drainage ditches are being dug, and hydraulic structures are being prepared.

As the threat of flooding increases, the work of enterprises, organizations and institutions stops, people are sent home or evacuated to safe areas.

In this case it is necessary:

Turn off water, gas and electricity;
extinguish burning heating stoves;
move valuable objects and belongings to the upper floors of buildings (attics), remove agricultural equipment to a safe place, bury, cover fertilizers and waste;
if necessary, cover the windows and doors of the first floors of houses with boards or plywood;
take with you personal documents placed in a waterproof bag, money and valuables, a first aid kit, a set of outerwear and shoes for the season, bed linen and toiletries, and a three-day supply of food. It is better to put things and food in suitcases (backpacks, bags);
arrive at the predetermined time at the evacuation assembly point for registration and departure to a safe area.

Actions when carrying out evacuation measures

If a flood finds you at home, you must:

Do not panic and do not lose composure;
as quickly as possible, occupy the nearest, safe, elevated place, the upper floors of buildings, the attic or roof of a house and be ready to evacuate by water, including using available watercraft;
take measures to allow rescuers to detect themselves in a timely manner. During daylight hours, this is achieved by hanging a white or colored panel in a high place, and at night - by giving light signals;
until help arrives, if you are not in danger, remain in the place you have chosen;
Self-evacuation to a non-flooded area should be carried out only in cases of the need to provide emergency medical care to victims. For independent evacuation, personal boats or cutters, rafts made of logs and other available materials are used. When evacuating, it is necessary to observe safety measures: enter the boat or boat one at a time, do not sit on board while they are moving, do not change places or push.

If you still find yourself in the water, you urgently need to go to an elevated place, and if in the forest, then climb onto a strong, spreading tall tree. If you still find yourself in the water, then swim to the nearest unflooded area not against the current, but at an angle to it. To do this, use all objects that can keep you on the water: logs, boards, pieces of trees, etc. In areas with a lot of algae or grass, avoid sudden movements to avoid getting entangled.

After the water has subsided, you must:

Return, if possible, to your place of residence, and before entering buildings, make sure that their structures have not undergone obvious destruction and do not pose a danger;
When inspecting the interior of a building, it is not recommended to use matches or candles as a light source due to the possible presence of gas. For these purposes, it is better to use electric lights;
Beware of broken or sagging electrical wires. It is prohibited to turn on electrical appliances until the condition has been checked by specialists. electrical network;
damage and destruction of water, gas and sewer lines must be immediately reported to the relevant utility services and organizations;
Products that have entered the water are strictly prohibited from being used as food until inspection by the sanitary and epidemiological service and without hot processing;
check drinking water supplies, and dry existing wells by pumping contaminated water from them.

The primary measures for providing medical assistance during floods are to remove victims from the water, warm them, and stimulate cardiac and respiratory activity.

It is better to swim to a drowning person from behind. As you approach, grab him by the head, arms, shoulders or collar, turn him face up and swim to the shore, working with your free arm and legs. If you use a boat to help a drowning person, then it is best to pull the person out of the water from the stern. If there is no boat, you can use available means - barrels, logs, wooden panels and doors, car cameras and other objects that can keep a person afloat.

Flood is a phase of the water regime of a river that can be repeated many times in different seasons of the year, characterized by an intense, usually short-term increase in flow rates and water levels, and caused by rain or snowmelt during thaws. Successive floods can cause flooding. Significant flooding may cause flooding. Floods are irregular. A significant increase in the speed and discharge of water flow during a flood is accompanied by an increase in water turbidity, reformation of the channel, and under favorable conditions leads to the emergence of a mudflow through the failure of the blind area and deep erosion of the channel.

Catastrophic flood - a significant flood resulting from intense melting of snow, glaciers, and heavy rains, forming a severe flood, which resulted in mass death of the population, farm animals and plants, damage or destruction of material assets, and damage to the environment . The term catastrophic flood is also applied to a flood that causes the same consequences.

Tsunamis are giant sea waves that arise as a result of the upward or downward displacement of extended sections of the seabed during strong underwater and coastal earthquakes.

Tsunami propagation speed from 50 to 1000 km/h; the height in the area of ​​occurrence is from 0.1 to 5 m, near the coast - from 10 to 50 m or more.

About 1000 cases of tsunamis are known, more than 100 of them with catastrophic consequences, causing complete destruction, washing away of structures and soil and vegetation cover (for example, in 1933 off the coast of Japan, 1952 in Kamchatka, etc.). 80% of tsunamis occur in the periphery Pacific Ocean, including the western slope of the Kuril-Kamchatka Trench. Based on the patterns of tsunami occurrence and propagation, the coast is divided into zones according to the degree of tsunami threat.

Measures for partial protection from tsunamis: creation of artificial coastal structures (breakwaters, breakwaters and embankments), planting forest strips along the ocean shores. IN THE USA. Japan and Russia have created warning services for the population about the approach of a tsunami, based on the advanced registration of earthquakes by coastal seismographs.

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.) In the territory

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

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);

With surge, storm and dam-burst floods in populated areas of southern Asia, Central and South America Various legends about the global flood are associated, 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 the opposite direction, already experiencing much greater resistance to the roughness of the bottom. 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 propagates further up the river, the lower the slope and more depth rivers. 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 reservoir, the shallower its depth, the closer its configuration to a circle or ellipse, the larger the size of the surges and surges of water.

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 rainfall, 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, the 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 created 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 River may rise to 17 m and flooding will 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. Damaged settlements, roads, power lines, agricultural land.

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, settlements are damaged, and enterprises are shut down. In July 1990, during a typhoon, more than two months of precipitation fell in Primorye. 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.

High waters 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 temperate zone and 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 in such a way that lakes of melt water can appear in the snow cover, bursting together 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, 100 livestock farms, etc. were destroyed. 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.

Zazhornye 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 jammed ice accumulations on the Angara and Amu Darya reaches 10–15 m, length – 25 km, reduction in the cross-sectional area of ​​the channel – 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. Due to gluttons in many areas of Siberia and the mountains Central Asia seasonal river ice is created - an obstacle 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 the Far East, on the Northern Dvina, Pechora, Western Dvina, and 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 of 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 (mostly 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 are intensifying 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 impervious 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 inundation 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 violated;

♦ 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, flood prevention measures 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.

Humanity has suffered from floods since ancient times. Each of us has heard the story of the Great Flood, which flooded the globe and destroyed all life except the “passengers” of Noah’s Ark.

Scientists believe that something similar took place in Mesopotamia in the third or fourth millennium BC. At that time, the populated lands in the valleys of the Tigris and Euphrates seemed to people like the whole Universe, so they associated large-scale floods with a global disaster.

As many years ago, today flooding is considered one of the most dangerous natural disasters and often leads to loss of life and economic damage. Why is this happening? And what are the consequences of floods?

What do you mean by flood?

A flood is a widespread inundation large areas water from rivers, lakes, seas, oceans. Many regions of the Earth are susceptible to such disasters. Floods often occur in the river valleys of Western Europe, on the Chinese Yellow and Yangtze rivers, in the USA and Canada.



In the territories of the former Soviet Union, floods most often affect the areas along the banks of the Dnieper, Amur and Volga.

Why do floods happen?

There are many reasons for floods. The most common are those that lead to rivers overflowing and overflowing along the coastal plains. Areas located in lowlands are characterized by periodically recurring floods associated with melting snow. Often in the spring, during ice drift, large blocks of snow and ice cause congestion in the river bed, resulting in water rising above the main level of the banks.

On islands and the mainland coast of seas and oceans, from time to time a so-called wind surge occurs, when, under the influence of strong winds, the water surface rises above sea level and floods large areas of land. More catastrophic are tsunami waves, which arise from tremors and eruptions of underwater volcanoes, and then hit the coast.

Other causes of floods include damage to reservoirs or dams, landslides that block river channels, as well as storm surges and seiches (standing waves in enclosed bodies of water - lakes, ponds).

What types of floods are there?

Depending on their scale, floods are divided into several types. Small ones occur mainly on small rivers and cover small areas. Their frequency is on average 5–7 years, and the degree of flooding does not exceed 10%. Dangerous floods cause more serious damage and inundate up to 20% of land, which disrupts people's lives and often requires their evacuation.



Particularly dangerous are natural disasters that cover the entire river basin and flood populated areas. As a result, there is a need for a massive export of population and valuables. The worst are catastrophic floods that completely paralyze industry and agricultural activity over large areas. They can lead to loss of life and humanitarian disasters that require the participation of the international community.

Consequences of floods

Major floods lead to irreversible consequences and cause enormous material damage. As a result of flooding, damage occurs to roads, infrastructure, residential buildings, tunnels, and bridges. Water destroys agricultural land, causes the death of domestic animals, and in particularly catastrophic cases, people die from flooding.

The main task of rescuers during natural disaster- this is searching for victims and providing assistance in the most short time. The success of rescue teams largely depends on a quick response to the current situation and the use of effective techniques for operational reconnaissance and detection of people in flooded areas.

The largest floods in history

Humanity knows many large floods that were catastrophic in nature. In 1953, storm surges off the coast of Western Europe caused many rivers to rise sharply, causing extensive property damage and the deaths of 2,000 people.



The 2004 tsunami, which flooded Indonesia, Thailand, India and several other Asian countries, is recognized as the deadliest in modern history. Waves rushing onto the shores Indian Ocean, penetrated deep into the coast and led to the death of more than 225 thousand people.

In 2005, Hurricane Katrina caused seawater to overflow from levees and flood more than 80% of the city of New Orleans, in which, according to various sources, between 1,300 and 1,600 people died.