The flooding
The dangers of flooding in almost all terrains. Overflow of the river the reasons leading to deluge. Flooding caused by snow melt in areas of abundant snow accumulation and large temperature changes. Increasing the speed of the melt due to rain.
| Рубрика | Экология и охрана природы |
| Вид | доклад |
| Язык | английский |
| Дата добавления | 21.12.2013 |
| Размер файла | 14,2 K |
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The Dangers Of Flooding
Floods are extremely dangerous, mainly because they can occur in almost all terrains and climates, but the immense power of water is greatly unpredictable. People are not particularly afraid of floods because, It is just water. Proof of this is found in the fact that 15% of America s homes are built on flood plains including the cities of New Orleans and Cincinnati. More and more, people are finding their way to the flood plains because of their flat, construction and friendly environment. Although a nice place to build, these houses lie on the edge of a very powerful and dangerous force. danger flood river snow
Floods often come from rivers. Left alone, a river system will seek equilibrium with the physical perimeters of its environment. This means that as a river passes through its various stages of fluvial geomorphic development, it demands space within which it can function. These spaces include the main channel, its tributaries, the flood plain and overflow land and stream terraces which normally define the lateral dimensions of a river s domain. The most important factor of the formation of floods from rivers is the river s water-holding capacity. If more water enters the river than the river is capable of holding, an overflow will occur which may lead to a flood. The way in which excess water enters a river is varied from place to place, environment to environment.
Overflows may be regular events to civilizations that have become accustomed to floods after thousands of years of dealing with them. Until shackled by several barrages, including the gigantic Aswan High Dam, the Nile regularly flooded the lower sections of its valley, thus supplying water for irrigation and silt to restore the soil s fertility. This regular flooding is known as seasonal flooding.
Flooding may also be caused by snow melt in areas of abundant snow accumulation and subsequently large temperature changes. The speed at which the snow melts depends primarily on energy input in the form of solar and terrestrial radiation upon the air temperature. Rainfall may also increase the melt speed, especially if the heat content of the rain is high. The severity of the melt is greatly affected by the packed snow s ability to absorb and hold the rain. This absorption factor is affected by the amount of rainfall, the thickness of the snow s layer, and the physical conditions of the snow itself. After all these factors play out, it is possible for the large snow accumulation to melt and flood the surrounding environment.
Topography, soils, and vegetation all play a role in flood potentials. Topography is a composite of slope steepness, slope length and slope gradation. A short slope reduces the time it takes water to reach surface material, especially if the slope is composed of rock. A steep slope will diminish the absorption capacity of a hillside.
Slope elevation also plays a part in the buildup of a flood. Slope elevation is the slope s position relative to prevailing wind and rain. In the Northern Hemisphere, heavy snow accumulation is exposed to the sun s radiation on the southern side more so than on the northern side. This factor accelerates and quickens water runoffs, leading to southern areas having more floods.
Precipitation is much heavier on wind facing slopes. This is caused by the geographic effect. As air is forced up the slope, it will cool rapidly and reach its condensation point/temperature. Depending on the condensation temperature, water droplets or ice particles may form to create heavy cloud formations. Considerable amounts of precipitation may fall from these clouds, leading to great flood potential.
Ground conditions are very important when it comes to floods. Rock surfaces as well as soil with a high clay content are very resistant to water absorption, thus increasing the possibility of floods. Many other factors control absorption rates of soil. Movement into the soil is mostly controlled by the texture or particle size, by the structure of the soil, and by the amount of organic material found in it. The greater the amount of organic material and the coarser the soil is, the more water can enter the soil. The infiltration of soil and the percolation within the soil is greatly affected by frozen material. In spring, some subsoils are still frozen. This will markedly slow down hydraulic conductivity. All these absorption blocks lead to heavy runoffs and high flood potentials.
Drowning, of course, is the most common way a flood will kill Kenny. If Kenny finds himself under the water fighting for air, he is in trouble. He may struggle for a while, holding his breath, but sooner or later if he does not get some air, he may pass out or he may take a big gulp of water because of his lungs insistence on breathing something in.
Once water enters the lungs, it washes away a substance called suffectant, which enables the alveoli to leach oxygen out of the air. The alveoli themselves, like clusters of membrane in the lungs, collapse because blood cannot get to the pulmonary artery. The artery constricts in an effort to send blood to areas of the lungs where there is oxygen. Unfortunately, the areas do not exist. The heart labors under critically low levels of oxygen and starts to beat erratically, like a bag full of worms, as one doctor put it. This erratic pumping of Kenny s heart is called ventricular fibrillation. The more irregular the heart beats, the less blood moves and the faster life functions decline. Children, like Kenny, who have proportionally better hearts than adults, can maintain a heartbeat for up to five minutes without air. Adults die faster. The heart beats less and less effectively until, finally, there is no movement at all.
The brain, however, is still alive. Kenny s central nervous system has no idea of what has happened. All it knows is that not enough oxygen is getting to the brain. His brain is still giving orders. Breathe! Pump! Circulate, but these orders cannot be obeyed. It is most likely that, at this point, Kenny s life functions will cease and he will die.
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