Поплава

Поплава: Аликанте (Шпанија), 1997.

Људи који траже уточиште од поплаве, Централна Јава, ca. 1865–1876.

Регуларно поплављивање у Венецији, Италија.

Поплава потока због тешке монсунске кише и високе плиме у Дарвину, Северна територија, Аустралија.

Поплава у Џеди, покрива улицу Краља Абдуле у Саудијској Арабији.

Поплава у близини Кеј Веста, Флорида, САД услед Урагана Вилме у октобру 2005.

Мања поплава на паркингу у близини Џунипер улице у Антланти на Божићно вече услед олује узроковане Ел Нињом

Поплава (инундација) је природна појава која означава неуобичајено високи водостај у рекама и језерима, због кога се вода из речног корита или језерске завале прелива преко обале те плави околно подручје. Такође означава и нешто ређу и обично краткотрајнију појаву која се догађа на обалама мора. Директива о поплавама Европске уније дефинише поплаву као покривање водом земљишта које нормално није покривено водом.

Узроци поплава река и језера најчешће су високе оборине, односно нагло топљење снега и леда, док је код мора и великих језера узрок обично потрес, неуобичајено снажна олуја или деловање вулкана.

Кориштење благодати које доносе поплаве, односно борба против њихових негативних последица, били су значајни фактори у развоју првих људских цивилизација. Системе за одбрану од поплава чине одбрамбени насипи.

Према узроцима настанка поплаве се могу поделити на:

• поплаве настале због јаких падавина
• поплаве настале због нагомилавања леда у рекама
• поплаве настале због клизања земљишта или потреса,
• поплаве настале због рушења бране или ратних разарања.

С обзиром на време формирања воденог таласа поплаве се могу разврстати на:

• мирне поплаве - поплаве на великим рекама код којих је потребно десет и више сати за формирање великог воденог таласа
• бујичне поплаве - поплаве на брдским водотоцима код којих се формира велики водени талас за мање од десет сати,
• акцидентне поплаве - поплаве код којих се тренутно формира велики водени талас рушењем водопривредних или хидроенергетских објеката

Могућности заштите

Техничке мере

• Редовна контрола водостаја и ознака наjризичнијих подручја с аутоматским алармирањем кризног центра.
• Стварање кривудавог тока реке или вештачких канала.
• Вештачки канали који преузимају вишак падавина.
• Вреће напуњене песком односно бране
• Вештачке бране код хидроцентрала
• Металне бране се учврсте помоћу ексера или шрафова на камену или бетонску подлогу
• Гумено црево, пречника око 1 метар, које се напуни водом. Сопственом тежином задржавају воду.
• Куће и други стамбени објекти у приземљу као и у подруму обложити битуменом који задржава воду, с тим да су врата и прозори такође заштићени од продирања воде

Организација и законодавство

• Благовремено евакуисање становништва
• Редовно обучавање становништва
• Забрана изградње кућа у опасним подручјима

Основни типови

Површинске поплаве

До поплава може доћи на равним или ниским областима кад је унос воде путем кише или тошљења снега бржи него што може било да се инфилтрира или да отече. Вишак се акумулира у месту, понекад до хазардних дубина. Површинско земљиште може да постане засићено, што ефективно зауставља инфилтрацију, где је горња граница подземне воде висока, као што је то случај у поплавним подручјима. Поплаву може изазвати интензивна киша једне или серије олуја. Infiltraцiција је исто тако спора до занемарљиве брзине кроз замрзнуто земљиште, стене, бетонске површине, плочњаке, или кровове. Површинско плављење починње на равним површинама као што су поплавна подручка и локалним депресијама које нису повезане са проточним каналима, пошто брзина копненог тока зависи од површинског нагиба. Ендорхејски базени могу да буду изложени површинском плављењу током периода кад преципитација премашује стопу евапорације.

Речна (каналске) поплаве

Поплаве се јављају код свих типова река, потокаа и канала, од најмањих ephemeral streams in humid zones to normally-dry channels in arid climates to the world's largest rivers. When overland flow occurs on tilled fields, it can result in a muddy flood where sediments are picked up by run off and carried as suspended matter or bed load. Localized flooding may be caused or exacerbated by drainage obstructions such as landslides, ice, debris, or beaver dams.

Slow-rising floods most commonly occur in large rivers with large catchment areas. The increase in flow may be the result of sustained rainfall, rapid snow melt, monsoons, or tropical cyclones. However, large rivers may have rapid flooding events in areas with dry climate, since they may have large basins but small river channels and rainfall can be very intense in smaller areas of those basins.

Rapid flooding events, including flash floods, more often occur on smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impermeable terrain, or normally-dry channels. The cause may be localized convective precipitation (intense thunderstorms) or sudden release from an upstream impoundment created behind a dam, landslide, or glacier. In one instance, a flash flood killed eight people enjoying the water on a Sunday afternoon at a popular waterfall in a narrow canyon. Without any observed rainfall, the flow rate increased from about 50 to 1.500 cu ft/s (1,4 to 42 m³/s) in just one minute. Two larger floods occurred at the same site within a week, but no one was at the waterfall on those days. The deadly flood resulted from a thunderstorm over part of the drainage basin, where steep, bare rock slopes are common and the thin soil was already saturated.

Flash floods are the most common flood type in normally-dry channels in arid zones, known as arroyos in the southwest United States and many other names elsewhere. In that setting, the first flood water to arrive is depleted as it wets the sandy stream bed. The leading edge of the flood thus advances more slowly than later and higher flows. As a result, the rising limb of the hydrograph becomes ever quicker as the flood moves downstream, until the flow rate is so great that the depletion by wetting soil becomes insignificant.

Естуарне и приобалне поплаве

Flooding in estuaries is commonly caused by a combination of sea tidal surges caused by winds and low barometric pressure, and they may be exacerbated by high upstream river flow.

Coastal areas may be flooded by storm events at sea, resulting in waves over-topping defenses or in severe cases by tsunami or tropical cyclones. A storm surge, from either a tropical cyclone or an extratropical cyclone, falls within this category. Research from the NHC (National Hurricane Center) explains: "Storm surge is an abnormal rise of water generated by a storm, over and above the predicted astronomical tides. Storm surge should not be confused with storm tide, which is defined as the water level rise due to the combination of storm surge and the astronomical tide. This rise in water level can cause extreme flooding in coastal areas particularly when storm surge coincides with normal high tide, resulting in storm tides reaching up to 20 feet or more in some cases."

Урбане поплаве

Urban flooding is the inundation of land or property in a built environment, particularly in more densely populated areas, caused by rainfall overwhelming the capacity of drainage systems, such as storm sewers. Although sometimes triggered by events such as flash flooding or snowmelt, urban flooding is a condition, characterized by its repetitive and systemic impacts on communities, that can happen regardless of whether or not affected communities are located within designated floodplains or near any body of water. Aside from potential overflow of rivers and lakes, snowmelt, stormwater or water released from damaged water mains may accumulate on property and in public rights-of-way, seep through building walls and floors, or backup into buildings through sewer pipes, toilets and sinks.

In urban areas, flood effects can be exacerbated by existing paved streets and roads, which increase the speed of flowing water.

The flood flow in urbanized areas constitutes a hazard to both the population and infrastructure. Some recent catastrophes include the inundations of Nîmes (France) in 1998 and Vaison-la-Romaine (France) in 1992, the flooding of New Orleans (USA) in 2005, and the flooding in Rockhampton, Bundaberg, Brisbane during the 2010–2011 summer in Queensland (Australia). Flood flows in urban environments have been studied relatively recently despite many centuries of flood events. Some recent research has considered the criteria for safe evacuation of individuals in flooded areas.

Катастрофалне поплаве

Catastrophic riverine flooding is usually associated with major infrastructure failures such as the collapse of a dam, but they may also be caused by drainage channel modification from a landslide, earthquake or volcanic eruption. Examples include outburst floods and lahars. Tsunamis can cause catastrophic coastal flooding, most commonly resulting from undersea earthquakes.

Узроци

Поплава услед циклона Худхуд у Визагапатнаму

Чиниоци успона

The amount, location, and timing of water reaching a drainage channel from natural precipitation and controlled or uncontrolled reservoir releases determines the flow at downstream locations. Some precipitation evaporates, some slowly percolates through soil, some may be temporarily sequestered as snow or ice, and some may produce rapid runoff from surfaces including rock, pavement, roofs, and saturated or frozen ground. The fraction of incident precipitation promptly reaching a drainage channel has been observed from nil for light rain on dry, level ground to as high as 170 percent for warm rain on accumulated snow.

Most precipitation records are based on a measured depth of water received within a fixed time interval. Frequency of a precipitation threshold of interest may be determined from the number of measurements exceeding that threshold value within the total time period for which observations are available. Individual data points are converted to intensity by dividing each measured depth by the period of time between observations. This intensity will be less than the actual peak intensity if the duration of the rainfall event was less than the fixed time interval for which measurements are reported. Convective precipitation events (thunderstorms) tend to produce shorter duration storm events than orographic precipitation. Duration, intensity, and frequency of rainfall events are important to flood prediction. Short duration precipitation is more significant to flooding within small drainage basins.

The most important upslope factor in determining flood magnitude is the land area of the watershed upstream of the area of interest. Rainfall intensity is the second most important factor for watersheds of less than approximately 30 sq mi or 80 km². The main channel slope is the second most important factor for larger watersheds. Channel slope and rainfall intensity become the third most important factors for small and large watersheds, respectively.

Time of Concentration is the time required for runoff from the most distant point of the upstream drainage area to reach the point of the drainage channel controlling flooding of the area of interest. The time of concentration defines the critical duration of peak rainfall for the area of interest. The critical duration of intense rainfall might be only a few minutes for roof and parking lot drainage structures, while cumulative rainfall over several days would be critical for river basins.

Низводни фактори

Water flowing downhill ultimately encounters downstream conditions slowing movement. The final limitation is often the ocean or a natural or artificial lake. Elevation changes such as tidal fluctuations are significant determinants of coastal and estuarine flooding. Less predictable events like tsunamis and storm surges may also cause elevation changes in large bodies of water. Elevation of flowing water is controlled by the geometry of the flow channel. Flow channel restrictions like bridges and canyons tend to control water elevation above the restriction. The actual control point for any given reach of the drainage may change with changing water elevation, so a closer point may control for lower water levels until a more distant point controls at higher water levels.

Effective flood channel geometry may be changed by growth of vegetation, accumulation of ice or debris, or construction of bridges, buildings, or levees within the flood channel.

Коинсиденција

Extreme flood events often result from coincidence such as unusually intense, warm rainfall melting heavy snow pack, producing channel obstructions from floating ice, and releasing small impoundments like beaver dams. Coincident events may cause extensive flooding to be more frequent than anticipated from simplistic statistical prediction models considering only precipitation runoff flowing within unobstructed drainage channels. Debris modification of channel geometry is common when heavy flows move uprooted woody vegetation and flood-damaged structures and vehicles, including boats and railway equipment. Recent field measurements during the 2010–11 Queensland floods showed that any criterion solely based upon the flow velocity, water depth or specific momentum cannot account for the hazards caused by velocity and water depth fluctuations. These considerations ignore further the risks associated with large debris entrained by the flow motion.

Some researchers have mentioned the storage effect in urban areas with transportation corridors created by cut and fill. Culverted fills may be converted to impoundments if the culverts become blocked by debris, and flow may be diverted along streets. Several studies have looked into the flow patterns and redistribution in streets during storm events and the implication on flood modelling.

Ефекти

Примарни ефекти

The primary effects of flooding include loss of life, damage to buildings and other structures, including bridges, sewerage systems, roadways, and canals.

Floods also frequently damage power transmission and sometimes power generation, which then has knock-on effects caused by the loss of power. This includes loss of drinking water treatment and water supply, which may result in loss of drinking water or severe water contamination. It may also cause the loss of sewage disposal facilities. Lack of clean water combined with human sewage in the flood waters raises the risk of waterborne diseases, which can include typhoid, giardia, cryptosporidium, cholera and many other diseases depending upon the location of the flood.

Damage to roads and transport infrastructure may make it difficult to mobilize aid to those affected or to provide emergency health treatment.

Flood waters typically inundate farm land, making the land unworkable and preventing crops from being planted or harvested, which can lead to shortages of food both for humans and farm animals. Entire harvests for a country can be lost in extreme flood circumstances. Some tree species may not survive prolonged flooding of their root systems.

Поплаве у Босни и Херцеговини 2014. године

Средином маја 2014. су се десиле велике поплаве након падавина које су превазишле рекорд, од како се врше мерења. Из корита су се излиле реке Босна, Дрина, Сана, Сава и друге. Поплављени су Маглај, Добој, Тузла, Приједор, Травник, Јања, Бијељина и многа друга места и насеља. Четири особе су погинуле, а на стотине су евакуисане из својих кућа и станова. У одбрану и санирање штете су укључени полиција, оружане снаге, цивилна заштита, хуманитарне, спортске организације и грађани.

Види још

• Поплаве у средњој Европи 2013.
• Поплаве на Балкану 2014.
• Brze poplave u Turskoj 2009.

Литература

• O'Connor, Jim E. & John E. Costa (2004) The World's Largest Floods, Past and Present: Their Causes and Magnitudes [Circular 1254], Washington, D.C.: U.S. Department of the Interior, U.S. Geological Survey.
• Thompson, M.T., (1964). Historical Floods in New England [Geological Survey Water-Supply Paper 1779-M]. Washington, D.C.: United States Government Printing Office.
• Powell, W. Gabe, 2009, Identifying Land Use/Land Cover (LULC) Using National Agriculture Imagery Program (NAIP) Data as a Hydrologic Model Input for Local Flood Plain Management, Applied Research Project, Texas State University–San Marcos

Спољашње везе

• Associated Programme on Flood Management from the World Meteorological Organization
• Flood and natural hazard research from Bushfire and Natural Hazards CRC
• International Flood Initiative from UNESCO