Natural Disaster || Flood
A flood is an overflow of water that submerges land that is usually dry. The European Union (EU) Floods defines Directive Flood as a flood that is usually covered by groundwater that is not covered by water. In the sense of "flowing water", the term may also apply to the flow of tides.
Flood water can occur as an overflow of water bodies, such as a river, lake, or ocean, in which the water is overweight or broken, resulting in some water escaping from its normal limits, or it may be caused by accumulation is. Of rainwater on a flood saturated land. While the size of a lake or other body of water will vary with seasonal variations in rainfall and snowmelt, these changes in size will not be considered significant unless they submerge flood property or domestic animals.
Flooding in rivers can also occur when flow rates exceed the capacity of the river channel, especially in waterways or bends. Floods often damage homes and businesses if they are in the natural floodplains of rivers. While the damage caused by river floods can be eliminated by moving away from rivers and other bodies of water, people traditionally live and work near rivers because the land is usually flat and fertile and because rivers are commercial. And provide easy travel and access to the industry.
Some floods develop slowly, while others, such as floods, can develop within minutes and without visible signs of rain. Additionally, flooding can be local, affecting a neighborhood or community, or very large, entire river valleys.
Etymology
The word "flood" comes from Old English flood, a term for Germanic languages (compare German flute, Dutch is seen from the same root as flux, float; Latin fluctus, also from flumen make comparisons). Divine myths are mythological stories of a great flood sent by a deity or gods to destroy civilization as an act of divine vengeance, and they are depicted in the mythology of many cultures.
Principal types
Areal
Flooding or flooding in low-lying areas can occur when the water supply is more rapid than rain or snowfall that can either infiltrate or escape. The excess accumulates in space, sometimes to dangerous depths. Surface soils can become saturated, effectively preventing infiltration, where the water table is shallow, such as from flooding, or from intense rain from one or one storm. Infiltration through land, rock, concrete, paving, or roofs is also negligible. Regional flooding begins in flat areas like floodplains and is not associated with a stream channel in local sediments, as the velocity of overland flow depends on the surface slope. Endorphin basins experience the time of flooding in the area when rainfall exceeds evaporation.
Riverine (Channel)
Floods occur in all kinds of river and river channels, from the smallest ephemeral streams in wet areas to normally dry channels in arid climates and the largest rivers in the world. When overland flow occurs in tilled fields, it can lead to a muddy flood where sediment is collected by runoff and transported as suspended matter or bed load. Localized flooding can be caused or exacerbated by drainage obstructions such as landslides, ice, debris, or beaver dams.
Slow growing floods most commonly occur in large rivers with large catchment areas. The increased flow may be the result of sustained rainfall, rapid thaw, monsoons, or tropical cyclones. However, large rivers can have rapid flooding in areas with a dry climate, as they may have large basins, but small river channels and rainfall can be very intense in smaller areas of those basins.
Rapid flood events, including flash floods, occur most frequently in smaller rivers, rivers with steep valleys, rivers that flow for much of their length over impervious terrain, or normally dry channels. The cause may be localized convective precipitation (intense thunderstorms) or the sudden release of an upstream reservoir created behind a dam, landslide, or glacier. In one case, a flash flood killed eight people enjoying the water on a Sunday afternoon at a popular waterfall in a narrow canyon. With no rainfall observed, the flow rate increased from approximately 50 to 1,500 cubic feet per second (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 in those days. The deadly flood was the result of a thunderstorm in part of the drainage basin, where steep, bare slopes are common and thin soil was already saturated.
Flash floods are the most common type of flooding in normally dry channels in arid areas, known as streams in the southwestern United States and many other names elsewhere. In this environment, the first flood water that arrives is depleted as it moistens the sandy stream bed. The leading edge of the flood thus advances more slowly than later and flows higher. As a result, the rising extremity of the hydrograph becomes faster and faster as the flood moves downstream until the flow is so great that the exhaustion from moistening the soil becomes negligible.
Estuarine and coastal
Estuary floods are commonly caused by a combination of tidal tides caused by winds and low barometric pressure and can be exacerbated by the high flow of the upstream river.
Coastal areas can be flooded by storms at sea, resulting in waves that exceed defenses or, in severe cases, by tsunami or tropical cyclones. A storm surge, whether from a tropical cyclone or an extratropical cyclone, falls into this category. Research from the National Hurricane Center (NHC) explains: "The storm surge is an abnormal increase in the water generated by a storm, beyond the expected astronomical tides. The storm surge should not be confused with the storm surge, 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 the storm surge coincides with normal high tide, resulting in storm surges reaching up to 20 feet or more in some cases. "
Urban flooding
Urban flooding is the flooding of land or property in a built environment, particularly in more densely populated areas, caused by rains that overwhelm the capacity of drainage systems, such as storm sewers. Although sometimes triggered by events such as flash floods or thaw, urban flooding is a condition, characterized by its repetitive and systemic impacts on communities, which can occur regardless of whether or not affected communities are within flood plains. designated or near any body of water. In addition to possible river and lake overflow, thawing, stormwater, or water released from damaged water pipes can collect on property and public rights-of-way, leak through building walls and floors or recede in buildings through sewer pipes, toilets and sinks.
In urban areas, the effects of flooding can be exacerbated by existing streets and paved roads, which increase the speed of water flow.
The flood flow in urbanized areas constitutes a danger for both the population and the infrastructure. Some recent catastrophes include the floods of Nimes (France) in 1998 and Vaison-la-Romaine (France) in 1992, the floods of New Orleans (USA) in 2005, and the floods in Rockhampton, Bundaberg, Brisbane during 2010 -2011 summer in Queensland (Australia). Flood flows in urban settings have been studied relatively recently despite many centuries of flooding. Some recent research has considered the criteria for the safe evacuation of people in flooded areas.
Catastrophic
Catastrophic river floods are generally associated with major infrastructure failures, such as a dam collapse, but can also be caused by drainage channel modification due to a landslide, earthquake, or volcanic eruption. Examples include outburst floods and lahars. Tsunamis can cause catastrophic coastal flooding, most commonly as a result of underwater earthquakes.
Causes
Upslope factors
The amount, location, and timing of water reaching a drainage channel due to natural precipitation and controlled or uncontrolled discharges from the reservoir determine flow at downstream locations. Some precipitation evaporates, some slowly seep through the ground, some may be temporarily sequestered as snow or ice, and some can produce rapid runoff from surfaces such as rocks, pavements, roofs, and saturated or frozen soils. The fraction of incident precipitation that quickly reaches a drainage channel has been observed from zero for light rain on dry and level ground to 170 percent for warm rain on accumulated snow.
Most precipitation records are based on a measured depth of received water within a fixed time interval. The frequency of a precipitation threshold of interest can be determined from the number of measurements that exceed that threshold value within the total time period for which observations are available. The individual data points are converted to intensity by dividing each depth measured by the time period between observations. This intensity will be less than the actual maximum intensity if the duration of the main event was less than the fixed time interval for which the measurements are reported. Convective precipitation events (thunderstorms) tend to produce storm events of shorter duration than orographic precipitation. The duration, intensity, and frequency of rainfall events are important for flood prediction. Short-term precipitation is more significant for flooding in small drainage basins.
The most important upward factor in determining the magnitude of the flood 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 square miles or 80 square kilometers. The slope of the main channel is the second most important factor for the largest river basins. The slope of the channel and the intensity of the rain become the third most important factor for the small and large basins, respectively.
Concentration time is the time required for runoff from the most distant point in the upstream drainage area to reach the point of the drainage channel that controls flooding in the area of interest. Concentration time defines the critical duration of maximum precipitation for the area of interest. The critical duration of heavy rain could be just a few minutes for rooftop drainage structures and parking lots, while rain accumulated over several days would be critical for river basins.
Downslope factors
Water flowing downhill ultimately encounters downstream conditions that slow down movement. The final limitation is often the ocean or a natural or artificial lake. Elevation changes, such as tidal fluctuations, are significant determinants of estuarine and coastal flooding. Less predictable events such as tsunamis and storm surges can also cause elevation changes in large bodies of water. The elevation of the flowing water is controlled by the geometry of the flow channel. Flow channel restrictions, such as bridges and canyons, tend to control the elevation of water above the restriction. The actual control point for any given drain range can change with the change in water elevation, so a closer point can control lower water levels until a more distant point controls higher water levels.
The effective geometry of the flood channel can be changed by the growth of vegetation, the accumulation of ice or debris, or the construction of bridges, buildings, or levees within the flood channel.
Coincidence
Excessive flooding events often result in coincidence, such as unusually hot, heavy rain that melts a heavy layer of ice, blocks floating ice channels, and leaves small reservoirs such as beaver dams is. Concomitant events can only make flooding wider than anticipated by simplified statistical prediction models considering flood runoff that flow into uninterrupted drainage channels. The debris modification of channel geometry is common when heavy flows transpose uprooted woody vegetation and flood-damaged structures and vehicles, including boats and rail equipment. Recent field measurements during the 2010–2011 Queensland floods have shown that no criteria based on flow criteria, water depth or specific timing can explain the hazards caused by water velocity and depth fluctuations. These considerations further ignore the risks associated with large debris carried by the flow movement.
Some researchers have noted the effect of storage created by cut and fill in storage corridors in urban areas. The sewer filler can become a reservoir if the sewers are blocked by debris, and the flow can be diverted along roads. Several studies have noted flow patterns on roads during storm events and involvement in redistribution and flood modeling.
Effects
Primary effects
The primary effects of flooding include loss of life, damage to buildings, and other structures including bridges, sewerage systems, roadways, and canals.
Floods also often cause damage to power transmission and sometimes power generation, followed by knockdown due to power loss. This includes drinking water treatment and loss of water supply, which can result in the loss of drinking water or severe water contamination. It may also be the cause of loss of sewage disposal facilities. Lack of clean water combined with human feces in flood waters increases the risk of waterborne diseases, which may include typhoid, Giardia, Cryptosporidium, cholera, and many other diseases depending on the location of the flood.
Damage to roads and transport infrastructure can make it difficult for those affected to seek assistance or provide emergency health treatment.
Flood waters typically devastate farmland, rendering the land useless and preventing crops from being sown or harvested, causing food shortages for both humans and farm animals. Entire crops for a country can be lost under extreme flooding. Some tree species cannot survive prolonged flooding of their root systems.
Secondary and long-term effects
Economic hardship due to a temporary decline in tourism, rebuilding costs, or a lack of food for price increases is a common one after the effects of severe flooding. Its effect on affected people can cause psychological harm to those affected, particularly where there are deaths, serious injuries, and property damage.
Urban flooding can lead to prolonged wet houses, which are associated with an increase in respiratory problems and other diseases. Urban flooding also has important economic implications for affected areas. In the United States, industry experts estimate that wet cellars can reduce property values by 10–25 percent and are one of the top reasons for not buying a home. According to the US Federal Emergency Management Agency (FEMA), about 40 percent of small businesses never open their doors after a flood disaster. In the United States, insurance is available to both homes and businesses against flood damage.
Benefits
Flooding (especially infrequent or minor floods) can also bring many benefits, such as recharging groundwater, making the soil more fertile, and increasing the nutrients in some soils. Floodwaters provide much-needed water resources in arid and semi-arid regions, where rainfall is unevenly distributed throughout the year and kills pests in cultivated lands. Freshwater flooding plays an important role in maintaining ecosystems, especially in river corridors, and is an important factor in maintaining flood biodiversity. Floods can spread nutrients to lakes and rivers, causing biomass and improvisational growth for a few years.
For some fish species, a flood can become a highly suitable location for spawning with some predators and increased levels of nutrients or food due to flooding. Fish, such as in-season fish, use floods to reach new habitats. Bird populations may also benefit from increased food production due to flooding.
Periodic flooding was necessary for the well-being of ancient communities along the Tigris-Euphrates Rivers, the Nile River, the Indus River, the Ganges, and the Yellow Rivermong among others. The feasibility of hydropower, a renewable source of hydropower, is also high in flood-prone areas.
Flood safety planning
At the most basic level, the best defense against flooding is to seek higher land for higher value use while balancing foresight risks with the benefits of occupying flood hazard areas. Important community-safety facilities, such as hospitals, emergency-handling centers, and police, fire and rescue services, should be built in areas with the least flood risk. Structures, such as bridges that should occur in unexpectedly flood-prone areas, should be designed to withstand flooding. Valuable uses can be made in flood risk areas that may be temporarily abandoned as people move back to safer areas when floods are imminent.
The plan for flood protection involves several aspects of analysis and engineering, including:
- Overview of past and present flood heights and floodplain areas,
- Statistical, hydrological and hydraulic model analysis,
- Mapping of floodplain areas and flood elevation for future flood scenarios,
- Long term land planning and regulation,
- Engineering design and construction of structures to control or withstand floods,
- Intermediate-term monitoring, forecasting, and emergency-response planning, and
- Short term monitoring, warning, and response operations.
Each topic presents different related questions with different scope and scale across time, place, and people involved. There have been attempts to understand and manage mechanisms at work in floodplains 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 the natural and beneficial effects of flooding To protect the works - without any adverse effect. A portfolio of best practice examples for disaster mitigation in the United States is available from the Federal Emergency Management Agency.
Control
In many countries around the world, waterways are often carefully managed due to floods. Defenses such as detention basins, levees, bunds, reservoirs, and heirs are used to prevent waterways from overflowing their banks. When these rescues fail, emergency measures such as sandbags or portable inflatable tubes are often used to prevent flooding. Coastal flooding has been addressed along coastal embankments in Europe and the Americas, such as sea walls, beach nourishment, and barrier islands.
In the riparian zone near rivers and drains, erosion control measures can be taken to try to slow down or reverse natural water forces, which make many waterways inoperative for a long time. Periodic flood control, such as dams can be constructed and maintained to reduce the severity and severity of dams such as floods. In the United States, the US Army Corps of Engineers maintains a network of such flood control dams.
In areas affected by urban flooding, one solution is the repair and expansion of man-made sewer systems and stormwater infrastructure. Another strategy is to reduce impervious 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 converted into parks and playgrounds that can sometimes tolerate flooding. An ordinance can be adopted by requiring developers to maintain Stormwater on site and protected by floodwalls and lewis, or buildings designed to withstand temporary flooding. Property owners can also invest in their solutions, such as re-landscaping their property and installing rain barrels, sump pumps and check valves to divert water flow from their building.
Analysis of flood information
A range of annual maximum flow rates in a stream reach can be analyzed statistically to estimate 100-year floods and floods at other recurrence intervals. Similar estimates from multiple sites in the same area of drainage may be related to the mean characteristics of each drainage basin to allow indirect estimation of flood recurrence intervals for streams without sufficient data for direct analysis.
Physical process models of channel access are generally well understood and will calculate the depth and area of given flow conditions for use in given channel conditions and flood flow and flood insurance. Conversely, to observe recent floods and channel conditions, a model can calculate the flow rate. Applied to different potential channel configurations and flow rates, a reach model can contribute to selecting an optimal design for a modified channel. Various access models are available as of 2015, either the 1D model (the flood level measured in the channel) or the 2D model (the variable flood depth measured across the flood range). The HEC-RAS, Hydraulic Engineering Center model, is one of the most popular software, if only because it is available free of charge. Other models such as TUFLOW combined with 1D and 2D components achieve flood depths in river banks and the entire floodplain.
Physical process models of full drainage basins are even more complex. While many processes are well understood at one point or for a small area, others are poorly understood at all scales, and process interactions may be unknown under normal or extreme climatic conditions. Basin models typically combine land-surface process components (to estimate how many models or how much snowfall occurs on a channel) with a range of access models. For example, a basin model can calculate runoff waterways that may have arisen from a 100-year storm, although the recurrence interval of a storm is rarely equal to the associated flood. Basin models are commonly used in flood forecasting and warning as well as in the analysis of the effects of land-use change and climate change.
Flood forecasting
Allow them to take precautions before they are prone to floods and warn people so that they can be prepared in advance for the flood situation. For example, farmers can remove animals from low-lying areas and put utility services into emergency provisions for re-route services if necessary. Emergency services may make provisions to provide sufficient resources ahead of time for emergencies as they arise. People can evacuate flood-affected areas.
To make the most accurate flood forecasts for waterways, it is best to have a long time-series of historical data, which is related to streamflows to measure past rainfall events. With real-time knowledge about the volatile potential in the areas capturing this historical information. , Such as excess capacity in reservoirs, ground-water levels, and the degree of saturation of field aquifers are also needed to make the most severe flood forecasts.
Radar estimates of rainfall and general weather forecasting techniques are also important components of good flood forecasting. In areas where good quality data are available, flood intensity and elevation can be estimated with very good accuracy and a lot of lead time. The output of a flood forecast is usually a maximum expected water level and the probable time of its arrival at major locations along the waterway, and may also allow for the calculation of a possible statistical return period of a flood. In many developed countries, flood-prone urban areas are protected from 100-year floods - that is floods that are about 63% likely to occur in any 100-year period.
According to the US National Weather Service (NWS) Northeast River Forecast Center (RFC) in Taunton, Massachusetts, one rule for predicting flooding in urban areas is that at least 1 inch (25 mm) of rain falls in about an hour. Time to initiate significant stagnation of water on impermeable surfaces. Many NWS RFCs regularly issue flash flood guidance and headwater guidance, indicating the typical amount of rainfall that is required to fall in periods of low water to flood or flood large water basins.
In the United States, an integrated approach to real-time hydrologic computer modeling using data obtained from the US Geological Survey (USGS), various cooperative observation networks, various automated weather sensors, NOAA National Operational Hydrological Remote Sensing Center (NHHRSC), Does. Hydropower companies, etc., combined with the expected rainfall and/or snowfall quantitative rainfall forecast (QPF), generated hydrological forecasts daily or as needed. The NWS also collaborates with Environment Canada on hydrologic forecasts affecting both the United States and Canada, like the area of the St. Lawrence Seaway.
The Global Flood Monitoring System, "GFMS", a computer device that maps flood conditions around the world, is available online. Users anywhere in the world can use GFMS to determine when flooding can occur in their area. The GFMS uses data from NASA's satellites from Earth and the global rainfall measurement satellite, "GPM." Precipitation data from the GPM are combined with a land surface model that determines vegetation cover, soil type, and terrain, how much water is soaking into the ground, and how much water is flowing into the stream.
Users can view statistics of rainfall, flow, water depth, and flooding every 3 hours on every 12 kilometer gridpoint on the global map. The forecast for these parameters is 5 days in the future. Users can view inundation maps (areas covered by water) in 1-kilometer resolution.
Deadliest floods
Below is a list of the deadliest floods worldwide, showing events with death tolls at or above 100,000 individuals.
Death toll
|
Event
|
Location
|
Date
|
2,500,000–3,700,000
|
1931 China floods
|
1931
| |
900,000–2,000,000
|
1887 Yellow River (Huang He) flood
|
1887
| |
500,000–700,000
|
1938 Yellow River (Huang He) flood
|
China
|
1938
|
231,000
|
Banqiao Dam failure, a result of Typhoon Nina. Approximately 86,000 people died from flooding and another 145,000 died during subsequent disease.
|
China
|
1975
|
230,000
|
Indian Ocean tsunami
|
2004
| |
145,000
|
1935 Yangtze river flood
|
China
|
1935
|
100,000+
|
St. Felix's Flood, storm surge
|
1530
| |
100,000
|
Hanoi and Red River Delta flood
|
1971
| |
100,000
|
1911 Yangtze river flood
|
China
|
1911
|
In myth and religion
Flood myths (great, civilization-devastating floods) are widespread in many cultures.
The religious text also describes flood events as a form of divine vengeance. As a prime example, the Flood legend of Genesis plays a major role in Judaism, Christianity and Islam.
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