The amount of water in water bodies is not the same throughout the year. Sometimes there is a sudden rise in the water level in the river or its significant decrease. For example, the flat river arteries of temperate latitudes are full of water in spring during the rapid melting of snow, when the channels are not able to accommodate the rapidly arriving water and flood, flooding the floodplain.
This phenomenon is called flood, but it is not the only one that causes significant fluctuations in the height of the water. After abnormal rains, a short-term sudden rise in the water level in the river is recorded. This flood is called a flood, and its consequences are called a flood. We will talk about how these phenomena differ and how they arise in this article.
High water
A pronounced and seasonally repeated river spill, called high water, is a consequence of the natural process of rapid snowmelt. This is a very long lasting action. It causes a significant increase in water in the river, usually provoking a way out of the usual channel and flooding of nearby floodplain meadows. By and large, this phenomenon cannot be regarded as a sudden rise in the water level in the river, since a similar situation is always predictable, but this condition differs from the usual one. During the flood, the lion's share of the total annual runoff is from 50 to 80%.
Seasonality of the phenomenon depends on the characteristic features of the water artery, its nutrition and the area where it flows. So, spring flood is inherent in most lowland water bodies with snow nutrition. A clear demonstration of such are the rivers flowing among the coniferous and mixed forests of the plains of Russia. It is snow nutrition that predominates in them, and since the peak of melting ice falls at the beginning of April, then flood occurs at the same time. Mountainous spills more often in the summer, because at that time active melting of glaciers begins, causing a sudden rise in water level in the river. Summer floods are also observed on rivers with rain feeding in the Far East monsoon climatic zones with characteristic dry winters and rainy summers.
The process of increasing water is uneven: in the first few days it arrives slowly, then it accelerates, often reaching 0.3-0.6 meters per day. The rise of water on small and medium rivers can be 2-4 m, on large water arteries - up to 20 m. Often, even from the expected arrival of water there are very serious consequences caused by large-scale spills.
In a word, a sudden rise in the water level in a river caused by floods is logical, and its seasonality is explained by the features of the natural zone where the river flows.
Flood duration
In small reservoirs, the water level returns to normal after 20-30 days. The highest point of water rise on them reaches at the end of the first week. On large navigable rivers, the duration of the flood is 2-3 months, and the peak of maximum rise is fixed for 20-30 days.
In contrast to the increase, the decline in the level occurs several times longer. Spring flood is usually accompanied by ice drift, the duration of which varies from 5 to 15 days.
The sudden rise in water level in the river, triggered by the flood
A phenomenon of a completely different order is considered to be a flood, the occurrence of which is impossible to predict. This is neither a matter of seasonality, nor periodicity, nor regularity, because it is impossible to foresee a spontaneous event. The flood is the consequences of the elements, resulting in a sudden short-term rise in the water level in the river. High water occurs at various times of the year. It is absolutely independent of river life processes and can be triggered by abnormal weather conditions - heavy rains, snowmelt, etc.
For example, monsoon rains in India and Pakistan cause river spills several times a year. The duration of the flood varies from 2-3 hours to 3-7 days.
