floods

Flooding - is a temporary flooding of a significant part of the land with water as a result of the action of the forces of nature. Flooding, depending on the causes that cause it, can be conditionally divided into 3 groups.

The first includes floods caused by heavy rainfall or intense snowmelt.

The damage to the national economy is caused by floods, which are a combination of flood waters with ice drift. An ice drift is usually accompanied by a jam or jams, which, in turn, cause an additional rise in the water level and the flooding of a new territory. In addition, when water breaks through an obstacle, a rapid wave can form, creating the danger of sudden flooding of the area located downstream.

The second group consists of floods that occur under the influence of surge winds. They are observed on sea coasts and at the mouths of rivers flowing into the sea. The surging wind retains water in the mouth, as a result of which its level in the river rises.

The third group includes floods caused by underwater earthquakes. Underwater earthquakes generate giant waves - tsunamis. Their propagation speed reaches 400-800 km/h.

Tsunami

Some earthquakes were accompanied by destructive waves that devastated the coast - tsunamis (a large wave flooding the bay). Tsunamis are long waves of a catastrophic nature, arising mainly as a result of tectonic movements on the ocean floor.

The wavelength of a tsunami ranges from 150 to 300 km. In the open sea, tsunamis are not very noticeable: their height is several tens of centimeters or a maximum of several meters. Having reached the shallow shelf, the wave becomes higher, rises and turns into a moving wall. Entering shallow bays, the wave becomes even higher. At the same time, it slows down and, like a giant shaft, rolls onto land. The speed of the tsunami is the higher, the greater the depth of the ocean. Tsunamis are most often caused by underwater earthquakes. Volcanic eruptions can serve as another source.

There is a tsunami intensity scale:

I - the tsunami is very weak, the wave is noted only by tide gauges.

II - weak tsunami, can flood a flat coast.

III - tsunami of medium strength. Flat coasts are flooded, light ships can be washed ashore. Port facilities suffer little damage.

IV - strong tsunami, the coast is flooded, coastal buildings and structures are damaged. Large sailing ships and small motor boats are thrown onto land and then washed back into the sea. The shores are littered with debris and debris.

V - very strong tsunami, coastal areas are flooded. Larger ships washed ashore. The damage is great. human sacrifice.

VI - catastrophic tsunami, complete devastation of the coast and coastal areas. The land is flooded. The largest ships are damaged. Many victims.

"Tsunami" means "wave in the harbor" in Japanese. This is a fairly accurate transfer of the essence of this phenomenon.

Away from the coast, in the open ocean, tsunamis are invisible. And as we know them, the waves become near the coast and in the harbors.

Let's look at what a tsunami is, what are the causes of a tsunami and their consequences?

In most cases (about 85%), tsunamis are caused by vertical displacements of the seabed at . At the same time, the subduction (subduction) of one lithospheric plate under another causes a sudden uplift of the latter, and with it the uplift of huge masses of water.

Surface waves diverge from the place of uplift. They reach the nearest coasts and are called local tsunamis. These waves can reach a height of 30 meters and cause great destruction on the coast near the epicenter of the earthquake.

But the uplift of the sea floor generates a series of underwater waves similar in nature to sound or shock waves.

They spread in the water column from the surface to the bottom of the ocean at a speed of 600-800 km/h. When such waves approach distant shores, their energy is concentrated due to a decrease in depth. There are surface waves, which fall on the shore. These tsunamis are called remote.

Such waves are capable of crossing the Pacific Ocean from Chile to Japan at a speed of 200 m/s in 22-23 hours.

In the ocean, due to its length of 200-300 km and a height of only 0.5 meters, they are not noticeable from the surface of the water and from the air.

Another cause of tsunamis is landslides above or below the water level. Such waves occur in 7% of cases and are of local importance. But their height at the same time can reach more than 20 meters and cause corresponding destruction. And under certain conditions, such as during the earthquake in Alaska and the landslide in Lituya Bay in 1958, the wave that reached the opposite shore of the bay had a height of 524 meters.

Approximately 5% of tsunamis are caused by volcanic eruptions. A classic example is the explosion of the Krakatoa volcano near the island of Java in 1883. The resulting waves caused the death of 36,000 people, and their effect was felt in all the harbors of the world.

In addition to the death of people, tsunamis cause flooding of significant coastal areas and soil salinization, destruction of buildings and structures, soil erosion, damage to ships moored near the coast.

To reduce the damage from the consequences of the tsunami, construction should be carried out outside the zone of their impact. If this is not possible, build buildings so that they take blows with their short side, or place them on strong columns. In this case, the wave will pass freely under the building without damaging it.

If there is a threat of a tsunami, ships moored near the coast must be taken out to sea.

Unfortunately, there are few of them. This is, first of all, an earthquake, even if it is weak. We cannot know where it happened, on land or under the seabed, how powerful it is, and whether it caused a tsunami. Therefore, being on the seashore, any earthquake should be considered a tsunami harbinger.

In some cases, before the arrival of the tsunami, atypical, untimely low tides are observed lasting from several minutes to half an hour.

The occurrence of such a low tide after an earthquake should alert. (photo)

Eyewitnesses often note the atypical behavior of animals that show concern, try to leave the coastal strip and, allegedly, climb to elevated places.

The combination of all the listed tsunami harbingers should not be in doubt, and the only correct action in this situation is to take rescue measures.

What to do in the event of a tsunami.

Areas along the coast, sea bays, harbors, the height of which does not exceed 15 meters above sea level, are considered to be tsunami hazardous. And if local tsunamis are expected, then areas with a height of less than 30 meters.

Being in such areas, you should think over in advance the sequence of your actions in case of danger.

We must make sure that the documents, the minimum necessary things and products are always at hand.

Arrange with family members for a rendezvous point after a disaster, consider evacuation routes from a dangerous coastal area, or designate places to escape if evacuation is not possible. It can be local hills or high capital buildings. It is necessary to move to them by the shortest route, avoiding low places. A distance of 2-3 km is considered safe. from the shore.

Be aware that when observing tsunami warnings, tremors, or local tsunami warnings, the time to rescue can be measured in minutes.

The occurrence of distant tsunamis is recorded by warning systems and the forecast is reported on radio and television. Such messages are preceded by the sounds of sirens.

It is impossible to predict the number, height of waves, as well as the interval between them. Therefore, after each wave, it is dangerous to approach the shore for 2-3 hours. It is advisable to use the gap between the waves to find the safest place.

Any earthquake felt on the seashore should be considered a tsunami hazard.

You can not approach the coast to look at the tsunami. It is believed that if you see a wave and are in a low place, it is too late to save yourself.

Compliance with these simple rules of conduct, knowledge of tsunami precursors could reduce the number of victims of the tsunami in the Indian Ocean in 2004. After all, according to eyewitnesses (this can also be seen on the recorded videos), many people used such a tsunami harbinger as the ebb before the arrival of the waves to walk along the seabed and collect marine animals. (photo)

With the right behavior, the number of people who survived could reach tens of thousands.

Knowing the causes of a tsunami, as well as ways to reduce the damage from the consequences of a tsunami, can one day help you save your life, the lives of your loved ones and property.

Tsunami video. (Japan, Fukushima, 2011 Earthquake of magnitude 6.6 on)

floods, tsunamis

Floods are called temporary flooding of a vast area as a result of a rise in the water level in a river, sea, lake. At the same time, such a rise in water can form if there are constant showers or snow melts. As a rule, floods are predicted and the population is notified in advance.

In most floods, people are advised to leave the building as it could collapse. Often, for people who have been affected by flooding, the government organizes special points where people gather and are transported to another city. Before leaving the house, everything that water can spoil should be transferred to the upper floors and other non-flooded places; turn off gas and electricity. Then, taking with you the documents and the most necessary things, a small supply of food and water, arrive at the collection point. Evacuation is carried out to large settlements located outside the flood zones. The above method of evacuation is carried out if the flood was known in advance and it was not sudden. If the flood is sudden, then another method of action is chosen. You should go up to the upper floors, and if the house is one-story, take the attic or go to the roof. The evacuation of the population in this case will be carried out on boats, boats, rafts and other floating facilities. During landing on them, strict discipline must be observed. One should go down into the boat one at a time, stepping on the middle of the flooring, and sit down only at the direction of the elder. During the movement of the boat, you can not change places, get on board; The bow of the boat should be kept perpendicular to the wave. After mooring, one of the passengers must go ashore and hold the boat overboard until all people are on land. Having caught the flood in the field, in the forest, you need to take the most elevated place, climb a tree.

Tsunamis are long waves generated by a powerful impact on the entire water column in the ocean or other body of water. Most tsunamis are caused by underwater earthquakes, during which there is a sharp displacement (raising or lowering) of a section of the seabed. Tsunamis are formed during an earthquake of any strength, but those that arise due to strong earthquakes reach a large force. Also, tsunamis can occur as a result of human actions, such as explosions. Also, tsunamis can be formed as a result of the fall of a large celestial body. During a tsunami, the local population is usually notified about the rules of action, since depending on the tsunami itself, the rules of action during it may be different.

Seeing a flood in a dream - to troubles and misfortunes.

If you see a flood in a dream, then this portends a long and exhausting struggle for a stable financial situation.

If you see in a dream that a flood is approaching your house, then in reality you will face difficulties and trials.

If you see in a dream that a flood is taking people away, then this portends you with heavy losses and hopelessness.

If you dream that a flood has happened and muddy water carries various garbage, this is a sign that they are trying to slander you.

If you dream that you are drowning during a flood, then this indicates that your affairs are upset and you do not see a way out of this situation.

If you see yourself drowning in muddy water, this is a warning of a severe debilitating disease.

If you see a flood in a dream from Thursday to Friday, then this indicates that you are wasting time on a fruitless struggle.

If you dream of a flood from Friday to Saturday, then you have to make a lot of efforts to overcome pressure from business partners.

If you see a flood from Saturday to Sunday, then this is a harbinger of a disease and health should be taken care of.

By the way, once in Paris a brilliant company gathered in the house of a noble gentleman. Among the guests was the famous soothsayer Cazotte.

The conversation turned to the future. The ladies began to ask about what awaits them all. Cazotte at first denied, and then told that one of those present - Mr. Condorcet - would poison himself in prison, and the other - Chamfort - would cut his veins.

The rest will be beheaded. “What gloomy predictions,” exclaimed one of those present, but the ladies will not be touched by this? “You are mistaken, madam,” replied Cazotte, “the ladies will face the same fate, you will be executed.”

These words made everyone uncomfortable. Then one of those present asked a question about what would happen to him.

“You will become a priest,” the soothsayer answered him. This message caused laughter from all those present, because La Harpe, to whom the last prediction was addressed, was known for his atheistic views. “What will happen to you?” he asked the soothsayer.

“They will cut off my head,” was the answer. No more questions were asked of Casotte that evening.

That night La Harpe had a dream. He saw that Paris was flooded with water. There was a huge flood.

He saw that rubbish, things, corpses were floating, all this was mixed up, and the water kept coming.

People try to escape, but they fail, because the water overwhelms them and drags them along. La Harpe saw with horror that the water turned red and bloody waves raged around.

La Harpe became frightened, he looked in a daze at the water approaching him. But horror pushed him to action, and he began to seek refuge from a terrible bloody flood.

But there was no escape anywhere. And suddenly he saw himself on the steps of a building. He looked up and realized that it was a church.

La Harpe did not tell anyone about his dream. But a few years later the French Revolution took place.

All Cazotte's predictions came true, and he himself was executed by guillotine.

Seeing with his own eyes all the horrors of the revolution, La Harpe took refuge in the church, he became a priest.

Once he saw from the gallery of the cathedral how crowds of people filled the streets of Paris.

At that moment, he remembered his dream, when a bloody flood flooded the streets of the city, and he himself found salvation on the steps of the temple.

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

Thus, the largest documented flood in the world occurred in China in the thirties of the last century, when the longest and full-flowing river of the country, the Yangtze, together with the neighboring Huang He, burst their banks after heavy rains, destroying dams and flooding more than 300 thousand hectares of fertile land ( in some areas, the water did not descend for about six months). When the river waters calmed down, the consequences of the flood were so catastrophic that the world shuddered: only according to official figures, the death toll exceeded 3.7 million people.

Flooding is the flooding of vast areas, which was caused by a rise in the water level in lakes, rivers, seas after heavy rainfall, snowmelt, dam break, which led to the release of water far beyond the coastline.

Although in most cases the population can be warned about the approach of a natural disaster, warnings are often ignored due to the fact that local residents refuse to leave their homes in the hope that the disaster will bypass them. And completely in vain: the advancing water does not spare anyone and not only destroys buildings (especially buildings with a shallow foundation and constructed of wood), but often leads to human casualties.

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

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

What are floods

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

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

Much more serious floods are classified as "Hazardous". They happen less frequently, once every 20-25 years. Covering rather large land plots located in river valleys, they cause significant material damage, flooding from 10 to 20% of crops. In some cases, even a partial evacuation of the population is required.

Floods, which hydrologists refer to as "Especially dangerous" occur once every fifty to a hundred years. Having overflowed its banks, the waters of the river completely fill the river basins, destroying from 50 to 70% of crops, and in some cases - settlements. As a result, all agricultural activities and the life of the region are paralyzed, the way of life of local residents is sharply disrupted, especially considering the fact that during especially dangerous floods mass evacuation of the inhabitants of the dangerous area is required.

The most dangerous types of floods in the world are classified as "Catastrophic" (it was this type of flood that befell China in the thirties of the last century). They flood the area of ​​one or more water systems, destroying almost all agricultural land, settlements (including cities), causing mass death of people. A country usually copes poorly with the consequences of floods of this magnitude and needs international assistance, since disasters often cause a humanitarian catastrophe.

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

1. Floods. This type of flood in the plains floods low areas and occurs in the spring during the melting of snow or after rain. It usually refers to small floods, but in some cases, if the soil was heavily oversaturated with moisture in autumn and severely frozen in winter, the consequences of floods can be catastrophic.
2. Flood. A leash is called a rapid, but short-term rise in the water level in rivers. This type of flood can occur several times a year, as it is primarily affected by heavy rainfall and in some cases by rapid snowmelt during thaws.
3. Congestion. The blockage is formed in early spring due to blockage of the rivers by an immobile block of ice or several ice floes, which slow down the river flow and cause the water to rise above the ice. This type of flood is characterized by a high but short-lived rise in the water level in the river.
4. Zazhor. A glacier flood appears due to an ice plug, which is a concentration of loose ice in the narrowing places of the river. During this flood, the water does not rise as much as during traffic jams, however, this flood is more prolonged.
5. Wind surge. This flood is characterized by a large rise in water and is caused by its wind. Since for this the air currents need to properly disperse the wave, the wind surge is usually fixed on the sea coast, at the mouth of the river, on large lakes, reservoirs. Predicting this flood is not easy, because it is characterized by a lack of periodicity and short duration.
6. Break in the reservoir. Floods of this type are formed due to the breakthrough of the reservoir, dam, dam. Despite their short duration, these floods are dangerous due to their suddenness and unpredictability, as a result of which a significant space is under water, and many objects that are in the way of the water are destroyed.

What to do in case of floods

In order to reduce the risk of occurrence and minimize the consequences of floods, flood protection is created in reservoirs - shallows are poured, rifts are deepened, and to regulate river flow, protective dams are built on the seashore, and reservoirs are built on rivers that equalize the flow of river flow, increasing it in summer, and reducing it. spring.

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

If a catastrophe of enormous proportions is coming, special services begin to evacuate the population (although these actions are far from always successful, since many refuse to leave their homes).

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

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

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

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

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