![]() ![]() In terms of precipitation amounts, record river stages, extent of flooding, persons displaced, crop and property damage, and flood duration, the Great Flood of 1993 was perhaps the worst hydrometeorological event to occur since the United States started to provide weather services in the late 1800s. Swift action is essential for the protection of life and property. ![]() There is little time between detection and flood crest. On small streams, especially near the headwaters of river basins, water levels may rise quickly in heavy rainstorms,Īnd flash floods can begin before the rain stops falling. Killing walls of water can reach 10–20 ft. Train effect storms can be part of multicell cluster or squall line storm systems.įlash-flood waves, moving at incredible speeds, can roll boulders, tear out trees, destroy buildings and bridges, and scour out new channels. Flash flooding can be produced by large, slow-moving storms or as a result of "train effect" storms (i.e., sequential mature storms that release precipitation over the same area). Typically, flash floods occur primarily at night and when there is an abundance of atmospheric moisture in addition, there is usually little, if any, vertical wind shear present. River Forecast Centers issue floodįorecasts and warnings when the rain that has fallen is enough to cause waterways to overflow their banks, and when melting snow combines with rainfall to produce similar effects. Flash floods frequently occur in seconds and minutes, while floods occur over hours and days. Flash floods are the result of too much rain falling in too small an area, in too short a time. HOW FLOODS HAPPENįloods begin when soil and vegetation cannot absorb falling rain or melting snow, or when water runs off the land in such quantities that it cannot be carried in normal stream channels or retained in natural ponds and human-made reservoirs. A total of 32,047 flash flood/flood events were recorded in 1985–2001. During the years 1985–2001, the total annual number of floods or flash floods ranged from 361 (1988) to 3,376 in 1998. These destructive overflows have caused property damage in some years estimated at more than $2 billion. Every year, floods drive some 75,000 Americans from their homes on the average, 127 persons are killed each year. The transformation of a tranquil river or normally dry wash into a destructive flood occurs hundreds of times each year, in every part of the United States. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |