Flood is an abundance of water that drowns normally dry soil. EU Flood Direction (EU) defines flooding as a cover by groundwater that is not normally covered by water. In the sense of "flowing water", the word can also be applied to tidal influx. Flood is a disciplinary hydrological study and an important concern in agriculture, civil engineering and public health.
Floods can occur as water overflows from water bodies, such as rivers, lakes, or oceans, where water flows or breaks the dikes, so some water that comes out of the boundary is usually, or may occur due to the accumulation of rainwater in saturated soils in a flooded area. While the size of the lake or other bodies of water will vary with changes in seasonal rainfall and melting snow, these size changes may not be considered significant unless they flood the property or drown the domestic animals.
Flooding can also occur in rivers when the flow rate exceeds the capacity of river channels, especially in bends or meanders in the waters. Floods often cause damage to homes and businesses if they are in the natural floodplain of the river. While river flood damage can be removed by moving away from rivers and other bodies of water, people traditionally live and work with rivers because the land is usually flat and fertile and because the river provides easy travel and access to trade and industry.
Some floods develop slowly, while others such as banjir bandang, can develop in just a few minutes and without visible signs of rain. In addition, floods can be local, impacting the environment or community, or very large, affecting the entire river basin.
Video Flood
Etymology
The word "flood" comes from the Old English flod , a word common to Germanic (compare German Flut , Dutch vloed from the root the same as seen in flow, float , also compared with Latin fluctus , flumen ). Flood myth is a mythical story about the great flood sent by gods or gods to destroy civilization as an act of divine retribution, and they are featured in many cultural mythologies.
Maps Flood
Primary type
Area
Floods can occur in flat areas or lowlands when water is supplied by rainfall or snow melting faster than water that can infiltrate or flow out. Excess builds up in places, sometimes to dangerous depths. Surface soils may become saturated, which effectively stop infiltration, where shallow water tables, such as floodplains, or from heavy rains from one or a series of storms. Infiltration is also slow to be ignored through frozen soil, rocks, concrete, paving, or roof. Signal flooding begins in flat areas such as floodplains and in local pressure is not connected to river channel, because the speed of ground flow depends on the slope of the surface. The endorphic basin may be flooded during periods when precipitation exceeds evaporation.
Riverine (Channel)
Floods occur in all types of river and stream channels, from the smallest ephemeral streams in the humid zone to the normally dry channels in dry climates to the largest rivers in the world. When ground flows occur in cultivated land, this can cause muddy floods where sediments are taken up with runoff and carried as suspended material or sleep loads. Local flooding can be caused or aggravated by drainage obstruction such as landslides, ice, debris, or beaver dams.
Slow-rising floods are most common in large rivers with large catchments. Increased flow may be the result of continuous rain, rapid melting of snow, rainy season, or tropical cyclone. However, large rivers may have rapid flood events in areas with dry climates, as they may have large basins but small river channels and rainfall can be very strong in smaller areas of the basin.
Rapid flood events, including banjir bandang, are more common in smaller rivers, rivers with steep valleys, rivers that flow for most of their lengths over fields that are not water-resistant, or normally dry channels. The cause may be local convective rain (intense lightning storm) or sudden release from an upstream reservoir created behind a dam, landslide, or glacier. In one instance, flash floods killed eight people who enjoyed water on Sunday afternoons at a popular waterfall in a narrow canyon. Without observed rainfall, the flow rate increases from about 50 to 1,500 cubic feet per second (1.4 to 42 m 3 /s) in just one minute. Two major floods occurred in the same location within a week, but no one was at the waterfall in those days. This deadly flood is caused by a storm over a section of the drainage channel, where the steep and deforested slopes are common soil and the thin soil is saturated.
Flash floods are the most common type of flood in the normally dry channels in the dry zone, known as arroyos in the southwestern United States and many other names elsewhere. In that arrangement, the first flood waters that had run out had dried up the sandy bottom of the river. The leading edge of the flood advances more slowly from the higher and slower currents. As a result, the hydrograph increase becomes faster as flood moves downstream, until the flow rate is so great that the thinning by soiling the soil becomes insignificant.
Estuary and beach
Floods in the estuary are generally caused by a combination of ocean waves caused by wind and low barometric pressure, and they may be exacerbated by high upstream river flows.
Coastal areas may be flooded by storms at sea, resulting in waves above defenses or in severe cases by tropical tsunamis or cyclones. Storm surge, whether from tropical cyclones or extratropical cyclones, falls into this category. Research from the NHC (National Hurricane Center) explains: "Storm surge is an abnormal increase of water produced by storms, over and above the predicted astronomical ebb and the storm surge should not be equated with storm surges, which are defined as water levels. a combination of storm waves and astronomical waves. This increase in water levels can cause extreme flooding in coastal areas especially when storm waves coincide with normal tidal waters, resulting in storm surges up to 20 feet or more in some cases. "
Urban flood
Urban floods are pools of land or property in built environments, especially in densely populated areas, caused by abundant rainfall capacity of drainage systems, such as storm sewers. Although sometimes triggered by events such as flash floods or snowmelt, urban flooding is a condition, characterized by repeated and systemic impacts on society, which can occur regardless of whether the affected communities are on specified floodplains or near the waters. In addition to the abundant potential of rivers and lakes, thawing of snow, storms or water released from damaged waterways can accumulate on property and on public roads, seeping through building walls and floors, or reserve buildings through sewer pipes, toilets and sinks..
In urban areas, the effects of flooding may be exacerbated by existing asphalt roads and roads, which increases the speed of the water flowing.
Flood flows in urban areas are a danger to the population and infrastructure. Some recent disasters include the inundation of NÃÆ'®mes (France) in 1998 and Vaison-la-Romaine (France) in 1992, the flood of New Orleans (USA) in 2005, and floods in Rockhampton, Bundaberg, Brisbane for the year 2010. -2011 summer in Queensland (Australia). Flooding that flows in urban environments has been studied relatively recently despite many centuries of flood events. Several recent studies have considered the criteria for safe evacuation of individuals in flooded areas.
Disaster
Catastrophic river floods are usually associated with major infrastructure failures such as the collapse of dams, but they may also be caused by modification of drainage channels from landslides, earthquakes or volcanic eruptions. Examples include blast and lava floods. Tsunamis can cause devastating coastal floods, most commonly occurring under submarine earthquakes.
Cause
Upslope factor
The amount, location, and time of the water reaching the drainage channel from natural precipitation and controlled or uncontrolled water release determines the flow at the downstream location. Some precipitates evaporate, some slowly seeping through the soil, some may be temporarily sequestered as snow or ice, and some may produce a rapid runoff from the surface including rocks, sidewalks, rooftops, and saturated or frozen soil. The incident precipitation fraction soon reaches the drainage channel has been observed from zero for light rain on the ground, dry rate to as high as 170 percent for warm rain on snow accumulation.
Most rainfall records are based on measured water depths received in fixed time intervals. The Frequency of the interest threshold can be determined from the number of measurements exceeding the threshold value in the total time period for which the observation is available. Individual data points are converted to intensity by dividing each depth as measured by the time period between observations. This intensity will be less than the actual peak intensity if duration of the rainfall event is less than the fixed time interval for reported measurements. Convective rainfall events (thunderstorms) tend to produce shorter duration of storms than orographic rainfall. The duration, intensity, and frequency of rain events are important for flood prediction. Short duration of rainfall is more significant against flooding in small drainage basins.
The most important upslope factor in determining the magnitude of floods is the area of ​​land from the upstream river basin of the intended area. Rainfall intensity is the second most important factor for watersheds less than about 30 square miles or 80 square kilometers. The main channel slope is the second most important factor for larger watersheds. The slope of the channel and the intensity of rain become the third most important factor for small and large watersheds, respectively.
Time Concentration is the time required for runoff from the farthest point of the upstream drainage area to reach the point of the drainage channel that controls the flooding of the area of ​​interest. The concentration time determines the critical duration of the peak rainfall for the desired area. The critical duration of intense rain may be only a few minutes for the roof drainage structure and parking lot, while cumulative rainfall for several days will be critical for river basins.
Downslope Factor
Flowing water eventually encounters downstream conditions that slow down movement. The last limitation is the frequency of oceans or natural or artificial lakes. Elevation changes such as tidal fluctuations are a significant determinant of coastal floods and estuaries. Unpredictable events such as tsunamis and storm surges can also cause elevation changes in large bodies of water. The flowing water level is controlled by the flow channel geometry. Flow channel restrictions such as bridges and canyons tend to control water levels above restrictions. The actual control points for each given drainage range may change with changes in water elevation, so a closer point can control the lower water level until a further point controls at higher water levels.
Effective flood channel geometry can be changed by vegetation growth, ice accumulation or debris, or construction of bridges, buildings, or embankments within the flood channel.
Coincidence
Extreme flood events are often caused by coincidences such as extreme precipitation, warm rainfall melts thick piles of snow, produces a drainage barrier from floating ice, and releases small impounds like beaver dams. Incidental events can cause large floods to be more frequent than anticipated from simple statistical prediction models as only rainfall runoff flows in unobstructed drainage channels. Modified rip line geometry debris occurs when heavy flow moves fallen wood vegetation and structures and vehicles damaged by floods, including boats and rail equipment. Recent field measurements during the Queensland 2010-11 flood indicate that any criterion solely based on flow velocity, water depth or certain momentum can not explain the dangers caused by the speed and fluctuations of water depth. This consideration ignores further the risks associated with large debris trapped by the flow movement.
Some researchers have mentioned the storage effect in urban areas with transport corridors made with cut and fill. The sand-filled culverts can be turned into impoundment if the culverts are blocked by debris, and the flow can be diverted along the road. Several studies have looked into flow patterns and redistribution on the streets during hurricanes and their implications on flood modeling.
Effects
Main effects
The main impacts of floods include loss of life, damage to buildings and other structures, including bridges, sewage systems, roadways, and canals.
Flooding also often damages the transmission of electricity and sometimes power generation, which then has a knock-on effect caused by loss of power. This includes loss of drinking water treatment and water supply, which may result in the loss of drinking water or severe water contamination. This can also lead to the loss of waste disposal facilities. Lack of clean water combined with human waste in the flood waters increases the risk of waterborne diseases, which can include typhus, giardia, cryptosporidium, cholera and many other diseases depending on the location of the flood.
Road damage and transport infrastructure can make it difficult to mobilize assistance to affected people or to provide emergency health care.
Flood water usually inundates agricultural land, makes land unusable and prevents crops from being planted or harvested, which can cause food shortages for both humans and livestock. All crops for a country can be lost in extreme flooding. Some tree species may not last long as they overwhelm their root system.
Secondary and long-term effects
Economic difficulties due to the temporary decline in tourism, the cost of rebuilding, or food shortages that lead to price increases are a common result of severe flooding. Impact on those affected can cause psychological damage to those affected, especially where death, serious injury and loss of property occur.
Urban flooding can lead to chronic wet homes, which are associated with increased respiratory problems and other diseases. Urban floods also have significant economic implications for the affected environment. In the United States, industry experts estimate that a wet basement can reduce property values ​​by 10-25 percent and is quoted among the main reasons for not buying a home. According to the US Federal Emergency Management Agency (FEMA), nearly 40 percent of small businesses never reopen their doors after a flood disaster. In the United States, insurance is available for flood protection both for home and business.
Benefits
Floods (especially floods that are more frequent or smaller) can also bring many benefits, such as groundwater filling, making soil more fertile and improving nutrients in some soils. Flood water provides a much needed source of water in dry and semi-arid regions where rainfall can be very uneven throughout the year and kill pests on farmland. Fresh water floods in particular play an important role in maintaining ecosystems in river corridors and are a key factor in maintaining the biodiversity of floodplains. Floods can spread nutrients to lakes and rivers, which can increase biomass and increase fisheries for several years.
For some species of fish, flooded floodplains can form locations that are particularly suitable for spawning with some predators and increase nutritional or dietary levels. Fish, like weather fish, use floods to reach new habitats. Bird populations can also take advantage of a boost in food production caused by flooding.
Periodic floods are very important for the welfare of ancient peoples along the Tigris-Euphrates River, Nile River, Indus River, Ganges River and Yellow River among others. The viability of hydropower, renewable energy sources, is also higher in flood prone areas.
Flood security planning
At the most basic level, the best defense against flooding is finding a higher place for high-value use while balancing predictable risks with the benefits of occupying a flood hazard zone. Important public safety facilities, such as hospitals, emergency operations centers, and police, firefighters and rescue services, should be built in areas least exposed to flooding. Structures, such as bridges, that can not be avoided are in flood-prone areas should be designed to withstand flooding. The areas most at risk of flooding can be exploited valuable that can be temporarily abandoned while people retreat to safer areas when floods are imminent.
Planning for flood safety involves many aspects of analysis and engineering, including:
- observed flood elevation and previous and current flood areas
- statistical analysis, hydrology, and hydraulics models,
- map flood areas and flood elevations for future flood scenarios,
- long term land use planning and regulation,
- engineering design and structural construction to control or withstand flooding,
- medium term monitoring, forecasting, and emergency response planning, and
- short-term monitoring, warning and response operations.
Each topic presents different questions but is related to the various scopes and timescale, space, and people involved. Efforts to understand and manage the mechanisms that work on floodplains have been carried out for at least six millennia.
In the United States, the Association of State Floodplain Managers works to promote education, policies, and activities that reduce current and future losses, costs, and human suffering caused by floods and to protect the natural and beneficial functions of the floodplains - all without causing adverse effects. impact. A sample portfolio of best practices for disaster mitigation in the United States is available from the Federal Emergency Management Agency.
Control
In many countries around the world, flood-prone waterways are often managed with care. Defenses such as places of detention, embankments, dikes, reservoirs and weirs are used to prevent overflow of water from their banks. When these defenses fail, emergency measures such as sandbags or portable inflatable tubes are often used to try to stem the flood. Coastal floods have been handled in parts of Europe and America with coastal defenses, such as sea walls, beach food, and barrier islands.
In riparian zones near rivers and streams, erosion control measures can be taken to try to slow or reverse the forces of nature that cause many waterways to tortuously over long periods of time. Flood control, such as dams, can be built and maintained over time to try to reduce the incidence and severity of the flood as well. In the United States, the US Army Engineer Corps maintains the dam network of flood control.
In areas susceptible to urban flooding, one solution is the improvement and extension of manmade drainage systems and stormwater infrastructure. Another strategy is to reduce non-flammable surfaces in roads, parking lots and buildings through natural drainage channels, porous paving, and wetlands (collectively known as green infrastructure or sustainable urban drainage systems (SUDS)). Areas identified as flood-prone can be turned into parks and playgrounds that can tolerate occasional floods. Ordinances can be adopted to require developers to hold rainwater on site and require buildings to be elevated, protected by flood walls and embankments, or designed to withstand temporary floods. Property owners can also invest in their own solutions, such as re-landscaping their property to take a steady stream of water from their buildings and install rain barrels, sump pumps, and check valves.
Analysis of flood information
A series of annual maximum flow rates within the flow range can be statistically analyzed to estimate 100 year floods and flooding other repetition intervals there. Similar estimates from many sites in the same area are hydrologically linked to the measurable characteristics of each basin drainage to allow indirect estimation of the flood repetition interval to reach the river without sufficient data for direct analysis.
The physical process model of the channel coverage is generally well understood and will calculate the depth and puddle area for given channel conditions and specified flow rates, such as for use in floodplain mapping and flood insurance. Conversely, given the recently observed flooded inundation areas and channel conditions, the model can calculate the flow rate. Applied to various channel configurations and potential flow rates, the range model can contribute to selecting the optimal design for the modified channel. Various range models are available by 2015, either 1D models (measured flood levels in the channel) or 2D models (variable flood depth measured along the floodplain). HEC-RAS, the Hydraulic Engineering Center model, is one of the most popular software, if only because it is available for free. Other models such as TUFLOW combine 1D and 2D components to obtain flood depth in both the river channel and the entire floodplain.
The physical process model of complete drainage drainage is even more complex. Although many processes are well understood at a point or for a small area, others are poorly understood at all scales, and process interactions under normal or extreme climatic conditions may be unknown. Basin models usually incorporate surface-surface process components (to estimate how much rainfall or melt snow reaches a channel) with a range of range models. For example, the basin model can calculate run-off hydrographs that may result from a 100-year storm, although the storm repetition interval is rarely the same as the associated flood. The basin model is commonly used in forecasting and flood warnings, as well as in the analysis of the effects of land use change and climate change.
Flood forecast
Anticipating floods before they occur allows for precautions to be taken and people are warned that they can be prepared in advance for flood conditions. For example, farmers can move animals from lowland areas and utility services may place emergency provisions for rescue services if required. Emergency services may also make provision for having enough resources available at the beginning of time to respond to an emergency when it occurs. People can evacuate areas to be flooded.
To make the most accurate flood forecast for aqueducts, it is best to have a series of long-term historical data linking river flows with measured rainfall events in the past. Combining this historical information with real-time knowledge of volumetric capacity in the catchment area, such as reservoir capacity in the reservoirs, groundwater levels, and saturation level of aquifers are also required to make the largest flood estimates.
Radar estimates rainfall and common weather forecasting techniques are also important components of good flood estimates. In areas where good quality data is available, the intensity and height of the flood can be predicted with good accuracy and plenty of lead time. The output from the estimated flood is usually the expected maximum water level and the likelihood of arrival time at major locations along the waterway, and it is also possible to calculate the possibility of flood statistical return periods. In many developed countries, urban areas at risk of flooding are protected against 100-year floods - a flood that has a probability of about 63% occurring over a 100-year period.
According to the Northeast River National Weather Board (NWS) of the Northeast River Estimation Center (RFC) in Taunton, Massachusetts, the rule of thumb for flood forecasting in urban areas is that it takes at least 1 inch (25 mm) of rainfall in about an hour's time to start water-making which is significant on the waterproof surface. Many NWS RFCs routinely publish Flood and Head Guides Guides, which show the amount of rainfall in general that needs to fall in a short time to cause flash floods or floods in larger water basins.
In the United States, an integrated approach to real-time hydrological computer modeling uses observed data from the US Geological Survey (USGS), cooperative observational networks, automated weather sensors, NOAA National Hydrological Sensing Center (NOHRSC), hydroelectric companies, etc. combined with quantitative rainfall forecasts (QPF) of expected rainfall and/or melting snow to produce daily or required hydrological estimates. NWS also works with Environment Canada on hydrological forecasts that affect the United States and Canada, such as the Saint Lawrence Seaway area.
The Global Flood Control System, "GFMS," a computer tool that maps the flood conditions worldwide, is available online. Users anywhere in the world can use GFMS to determine when a flood can occur in their area. GFMS uses rainfall data from NASA's Earth observation satellite and the Global Measurement Measurement satellite, "GPM." Rainfall data from GPM is combined with a soil surface model that combines vegetation cover, soil type, and terrain to determine how much water is permeating into the soil, and how much water flows into the stream.
Users can view statistics for rainfall, river flow, water depth, and flood every 3 hours, in every 12 kilometers of grid on the global map. The forecast for this parameter is 5 days ahead. Users can zoom in to see the flood map (the area estimated to be covered by water) in the 1 kilometer resolution.
Most Flood
Below is the list of the most deadly floods in the world, showing events with casualties in or over 100,000 people.
In myth and religion
Flood myths (massive floods that destroy civilization) are widespread in many cultures.
Flood events in the form of a divine retribution have also been described in religious texts. As a prime example, the flood story of Genesis plays an important role in Judaism, Christianity and Islam.
See also
References
Bibliography
- O'Connor, Jim E. & amp; John E. Costa (2004) The Largest Flood of the World, Past and Present: Causes and Their Magnitude [Circular 1254], Washington, D.C.: US Department of State, US Geological Survey.
- Thompson, M.T., (1964). Flood History in New England [Geological Survey Water-Supply Paper 1779-M]. Washington, D.C.: Printing Office of the United States Government.
- Powell, W. Gabe, 2009, Identifying Land Use/Land Use (LULC) Using National Agricultural Program Data (NAIP) Data as Hydrological Input Entry for Local Flood Management, Applied Research Projects, Texas State University-San Marcos
External links
- Flood Management Program of the World Meteorological Organization
- Flood research and natural hazards from the CRC's Natural Fire and Hazardous Nature
- International Flood Initiative from UNESCO
Source of the article : Wikipedia
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