There arefewplaces on Earth where people need not beconcernedaboutflooding.Any place where rain falls isvulnerable,although rain is not the onlyimpetusfor flood.
A floodoccurswhen water overflows orinundatesland that's normally dry. This can happen in amultitudeof ways. Most common is when rivers orstreamsoverflow theirbank.Excessiverain, aruptureddamorlevee,rapid ice melting in the mountains, or even an unfortunately placedbeaverdam canoverwhelma river and send it spreading over theadjacentland, called afloodplain.Coastalflooding occurs when a large storm or tsunami causes the sea tosurgeinland.
Most floods take hours or even days to develop, giving residentsampletime to prepare orevacuate. Othersgeneratequickly and with little warning. Theseflashfloods can be extremely dangerous,instantlyturning ababblingbrookinto athunderingwall of water andsweepingeverything in itspathdownstream.
Moving water has awesomedestructivepower. When a river overflows its banks or the sea drives inland, structures poorly equipped towithstandthe water's strength are no match. Bridges, houses, trees, and cars can be picked up and carried off. Theerosiveforce of moving water candragdirtfrom under a building'sfoundation,causing it to crack andtumble.
When floodwatersrecede,affected areas are oftenblanketedinsiltand mud. The water and landscape can becontaminatedwithhazardousmaterials, such as sharpdebris,pesticides,fuel, anduntreatedsewer. Potentially dangerousmoldbloomcan quickly overwhelm water-soakedstructures. Residents of flooded areas can be left without power and clean drinking water, leading tooutbreaksof deadly waterborne diseases like typhoid, hepatitis A, and cholera.
But flooding, particularly in river floodplains, is as natural as rain and has been occurring for millions of years. Famouslyfertilefloodplains like the Mississippi Valley in the American Midwest, the Nile River valley in Egypt, and the Tigris-Euphrates in the Middle East have supported agriculture formillenniabecause annual flooding has left millions of tons ofnutrient-rich siltdepositbehind.
Most flood destruction isattributableto humans' desire to live nearpicturesquecoastlines and in rivervalley.Aggravatingthe problem is atendencyfor developers tobackfilland build on wetlands that would otherwise act as natural floodbuffers.
Many governmentsmandatethat residents of flood-proneareaspurchasefloodinsuranceand build flood-resistant structures. Massive efforts tomitigateand redirectinevitablefloods have resulted in some of the most ambitious engineering efforts ever seen, including New Orleans's extensive levee system and massivedikesand dams in the Netherlands. And highly advanced computer modeling now lets disaster authoritiespredictwith amazing accuracy where floods will occur and howseverethey'relikelyto be.
Henüz oylanmamış. İlk oylayan siz olun!
Email Adresiniz :
(Görüşünüzün Sonucunu Almak İçin E-Mail Adresinizi Girebilirsiniz.)