|Flood is a significant submersion of terrain with water as a result
of rise in water levels in river, lake or sea, which is caused by
various reasons and leading to extraneous consequences. Let us review
the major flood causes.
Melting of snow during springs on plains or melting of snow during
spring-summer and rain residues in mountains. Snow melt floods recur
periodically in the same season. They are characterized by significant
and increase in water levels for a longer duration.
Jam and obstructions:
Floods occur due to significant resistance to water stream, on
isolated sections of riverbed, due to the accumulation of ice at
narrow spots or river curves during freezing of river (jamming) or ice
drift (obstructing). Obstructing floods occur at the end of winter or
at the beginning of spring. They are characterized by high and in
comparison, short-lived rise in water levels of river. Jamming floods
occur at the onset of winter and are characterized by significant (but
less than in the case of locking floods) rise in water levels and more
significant flood duration.
Due to high tides in firths and on windy sections of sea shores, large
lakes, water basins. Floods are possible at any time of the year.
Floods are characterized by the absence of periodicity and significant
rise in water levels.
Flood (deluge), is formed during breaches in barrages.
Excess of water from water basins or reservoirs, formed due to the
breaches in water front dines (dams, barrages etc) or during emergency
release of water from water basins and also in case of breach in
natural barrage, formed by nature during earthquakes, landslides,
landslips and avalanches. Floods are characterized by the formation of
high tides, leading to inundation of large territories and destruction
or damaging the objects (buildings, structures and etc), encountered
along its path.
In comparison, cause insignificant damage. Occupy few coastal
territories. Inundate less than 10% of agricultural lands. Almost, do
not disrupt the life of population. Recurrence: 5 - 10 years.
Cause appreciable material and moral loss and occupy, in comparison,
more lands of river valley and inundate approximately 10-15% of
agricultural lands. Appreciably disrupt the agricultural and domestic
life of the population. Lead to partial evacuation of population.
Recurrence: 20-25 years.
Cause appreciable material damage, occupy entire river basins.
Inundate approximately 50-70% of agricultural lands, several inhabited
localities. Paralyze economical activities and abruptly disrupt the
life of populace. Lead to mass evacuation of population and material
valuables from the flooded zone and protection of most important
objects. Repeatability: 50-100 years.
Cause huge material losses and leads to death of persons, occupies
vast territories within the limits of single or several river systems.
Inundate more than 70% of agricultural lands, many inhabited
localities, industrial enterprises and engineering service lines.
Flood completely paralyses economic and production activities,
temporarily changes the way of life of populace. Recurrence: 100 - 200
Melting of snow;
On coasts and islands, floods can occur as a result of submersion of
riverside with waves, formed during earthquakes or eruption of
volcanoes in ocean. Similar floods are not rare on the shores of Japan
and on other islands of Pacific Ocean.
Flooding occur on many rivers of Western Europe - Danube, Sen, Rhone,
Po and other rivers and also on the rivers Yangtse and Huang He
(Yellow river) in China, Mississippi and Ohio in USA.
Most effective method to abate the floods on rivers is to regulate the
river runoff by creating water basins. Dams are built to fight the
floods on seashores.|