Flood management or flood control are methods used to reduce or prevent the detrimental effects of flood waters. Flooding can be caused by a mix of both natural processes, such as extreme weather upstream, and human changes to waterbodies and runoff. Flood management methods can be either of the structural type (i.e. flood control) and of the non-structural type. Structural methods hold back floodwaters physically, while non-structural methods do not. Building hard infrastructure to prevent flooding, such as , is effective at managing flooding. However, it is best practice within landscape engineering to rely more on soft infrastructure and natural systems, such as and Floodplain, for handling the increase in water.
Flood management can include flood risk management, which focuses on measures to reduce risk, vulnerability and exposure to flood disasters and providing risk analysis through, for example, flood risk assessment.
As climate change has led to increased flood risk an intensity, flood management is an important part of climate change adaptation and climate resilience.
Terminology
Flood management is a broad term that includes measures to control or mitigate flood waters, such as actions to prevent floods from occurring or to minimize their impacts when they do occur.
Flood management methods can be structural or non-structural:
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Structural flood management (i.e.: flood control) is the reduction of the effects of a flood using physical solutions, such as , , dredging and diversions.
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Non-structural flood management includes land-use planning, advanced warning systems and flood insurance. Further examples are: "zoning ordinances and codes, flood forecasting, flood proofing, evacuation and channel clearing, flood fight activities, and upstream land treatment or management to control flood damages without physically restraining flood waters".
There are several related terms that are closely connected or encompassed by flood management.
Flood management can include flood risk management, which focuses on measures to reduce risk, vulnerability and exposure to flood disasters and providing risk analysis through, for example, flood risk assessment.[IPCC, 2022: Annex II: Glossary Möller,. In: Climate Change 2022: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change H.-O.. Cambridge University Press, Cambridge, UK and New York, NY, USA, pp. 2897–2930, ]
Flood control, flood protection, flood defence and flood alleviation are all terms that mean "the detention and/or diversion of water during flood events for the purpose of reducing discharge or downstream inundation".
Flood mitigation is a related but separate concept describing a broader set of strategies taken to reduce flood risk and potential impact while improving resilience against flood events. These methods include prevention, prediction (which enables flood warnings and evacuation), proofing (e.g.: zoning regulations), physical control (nature-based solutions and physical structures like dams and ) and insurance (e.g.: flood insurance policies).
Flood relief methods are used to reduce the effects of flood waters or high water levels during a flooding event.
Causes of flooding
Precipitation, absorption, and runoff
Flood levels: blunting the peak
Water levels during a flood tend to rise, then fall, very abruptly. The peak flood level occurs as a very steep, short spike; a quick spurt of water. Anything that slows the
surface runoff (marshes, meanders, vegetation, porous materials, turbulent flow, the river spreading over a floodplain) will slow some of the flow more than other parts, spreading the flow over time and blunting the spike. Even slightly blunting the spike significantly decreases the peak flood level. Generally, the higher the peak flood level, the more flood damage is done. Modern flood control seeks to "slow the flow", and deliberately flood some low-lying areas, ideally vegetated, to act as sponges, letting them drain again as the floodwaters go down.
Purposes
Where floods interact with housing, industry and farming that flood management is indicated and in such cases environmentally helpful solutions may provide solutions.
Natural flooding has many beneficial environmental effects.
This kind of flooding is usually a seasonal occurrence where floods help replenish soil fertility, restore
and promote
biodiversity.
Reducing the impacts of floods
Flooding has many impacts. It damages property and endangers the lives of humans and other species. Rapid water runoff causes soil erosion and concomitant sediment deposition elsewhere (such as further downstream or down a coast). The spawning grounds for fish and other wildlife habitats can become polluted or completely destroyed. Some prolonged high floods can delay traffic in areas which lack elevated roadways. Floods can interfere with drainage and economical use of lands, such as interfering with farming. Structural damage can occur in
, bank lines, sewer lines, and other structures within floodways. Waterway navigation and hydroelectric power are often impaired. Financial losses due to floods are typically millions of dollars each year, with the worst floods in recent U.S. history having cost billions of dollars.
Protection of individual properties
Property owners may fit their homes to stop water entering by blocking doors and air vents,
waterproofing important areas and
the edges of the building. Private precautionary measures are increasingly important in flood risk management.
Flood mitigation at the property level may also involve preventative measures focused on the building site, including scour protection for shoreline developments, improving rainwater in filtration through the use of permeable paving materials and grading away from structures, and inclusion of , wetlands or swales in the landscape.
Protection of communities
When more homes, shops and infrastructure are threatened by the effects of flooding, then the benefits of protection are worth the additional cost. Temporary flood defenses can be constructed in certain locations which are prone to floods and provide protection from rising flood waters. Rivers running through large urban developments are often controlled and channeled. Water rising above a
Canals full capacity may cause flooding to spread to other
and areas of the community, which causes damage. Defenses (both long-term and short-term) can be constructed to minimize damage, which involves raising the edge of the water with
levees, embankments or walls. The high population and value of infrastructure at risk often justifies the high cost of mitigation in larger urban areas.
Protection of wider areas such as towns or cities
The most effective way of reducing the risk to people and property is through the production of flood risk maps. Most countries have produced maps which show areas prone to flooding based on flood data. In the
United Kingdom, the Environment Agency has produced maps which show areas at risk. The map to the right shows a flood map for the
York, including the floodplain for a 1 in 100-year flood (dark blue), the predicted floodplain for a 1 in 1000 year flood (light blue) and low-lying areas in need of flood defence (purple). The most sustainable way of reducing risk is to prevent further development in flood-prone areas and old waterways. It is important for at-risk communities to develop a comprehensive Floodplain Management plan.
In the US, communities that participate in the National Flood Insurance Program must agree to regulate development in flood-prone areas.
Strategic retreat
One way of reducing the damage caused by flooding is to remove buildings from flood-prone areas, leaving them as parks or returning them to wilderness. Floodplain buyout programs have been operated in places like New Jersey (both before and after
Hurricane Sandy),
Charlotte, North Carolina,
and
Missouri.
In the United States, FEMA produces flood insurance rate maps that identify areas of future risk, enabling local governments to apply zoning regulations to prevent or minimize property damage.
Resilience
Buildings and other urban infrastructure can be designed so that even if a flood does happen, the city can recover quickly and costs are minimized. For example, homes can be put on stilts
or build on an elevated level.
Electrical and HVAC equipment can be put on the roof instead of in the basement, and subway entrances and tunnels can have built-in movable water barriers.
New York City began a substantial effort to plan and build for flood resilience after
Hurricane Sandy.
Flood resilience technologies support the fast recovery of individuals and communities affected, but their use remains limited.
Climate change adaptation
Structural methods
Some methods of flood control have been practiced since ancient times.
["Flood Control", MSN Encarta, 2008 (see below: Further reading).] These methods include planting vegetation to retain extra water, terracing hillsides to slow flow downhill, and the construction of floodways (man-made channels to divert floodwater).
[ Other techniques include the construction of levees, lakes, dams, reservoirs,][ to hold extra water during times of flooding.
]
Dams
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The term dry dam refers to a dam that serves purely for flood control without any conservation storage (e.g. Mount Morris Dam, Seven Oaks Dam).
Diversion canals
Floodplains and groundwater replenishment
Excess water can be used for groundwater replenishment by diversion onto land that can absorb the water. This technique can reduce the impact of later droughts by using the ground as a natural reservoir. It is being used in California, where orchards and vineyards can be flooded without damaging crops,
River defenses
In many countries, rivers are prone to floods and are often carefully managed. Defenses such as levees, bunding, reservoirs, and are used to prevent rivers from bursting their banks. A weir, also known as a lowhead dam, is most often used to create water mill, but on the Humber River in Toronto, a weir was built near Raymore Drive to prevent a recurrence of the flood damage caused by Hurricane Hazel in October 1954.
The Leeds flood alleviation scheme uses movable weirs which are lowered during periods of high water to reduce the chances of flooding upstream. Two such weirs, the first in the UK, were installed on the River Aire in October 2017 at Crown Point, Leeds city centre and Knowsthorpe. The Knostrop weir was operated during the 2019 England floods. They are designed to reduce potential flood levels by up to one metre.
Coastal defenses
is addressed with coastal defenses, such as , beach nourishment, and .
Tidal barrage are used in conjunction with Levee and culverts. They can be placed at the mouth of streams or small rivers, where an estuary begins or where tributary streams, or drainage ditches connect to sloughs. Tide gates close during incoming tides to prevent tidal waters from moving upland, and open during outgoing tides to allow waters to drain out via the culvert and into the estuary side of the dike. The opening and closing of the gates is driven by a difference in water level on either side of the gate.
Flood barrier
Self-closing flood barrier
The self-closing flood barrier (SCFB) is a flood defense system designed to protect people and property from inland waterway floods caused by heavy rainfall, gales, or rapid melting snow. The SCFB can be built to protect residential properties and whole communities, as well as industrial or other strategic areas. The barrier system is constantly ready to deploy in a flood situation, it can be installed in any length and uses the rising flood water to deploy.
Temporary perimeter barriers
When permanent defenses fail, emergency measures such as , inflatable impermeable sacks, or other temporary barriers are used.
In 1988, a method of using water to control flooding was discovered. This was accomplished by containing 2 parallel tubes within a third outer tube. When filled, this structure formed a non-rolling wall of water that can control 80 percent of its height in external water depth, with dry ground behind it. Eight foot tall water filled barriers were used to surround Fort Calhoun Nuclear Generating Station during the 2011 Missouri River Flooding. Instead of trucking in sandbag material for a flood, stacking it, then trucking it out to a hazmat disposal site, flood control can be accomplished by using the on site water. However, these are not fool proof. A high long water filled rubber flood berm that surrounded portions of the plant was punctured by a skid-steer loader and it collapsed flooding a portion of the facility.
AquaFence consists of interlocking panels which are waterproof and puncture-resistant, can be bolted down to resist winds, and use the weight of floodwater to hold them in place.
Other solutions, such as HydroSack, are polypropylene exteriors with wood pulp within, though they are one-time use.
Non-structural methods
Flood risk assessment
There are several methods of non-structural flood management that form part of flood risk management strategies. These can involve policies that reduces the amount of urban structures built around floodplains or flood prone areas through land zoning regulations.
Flood risk management aims to reduce the human and socio-economic losses caused by and is part of the larger field of risk management. Flood risk management analyzes the relationships between physical systems and socio-economic environments through flood risk assessment and tries to create understanding and action about the risks posed by flooding. The relationships cover a wide range of topics, from drivers and natural processes, to models and socio-economic consequences.
This relationship examines management methods which includes a wide range of flood management methods including but are not limited to flood mapping and physical implication measures.
Flooding and flood risk are especially important with more extreme weather and sea level rise caused by climate change as more areas will be effected by flood risk.
Flood mapping
Flood mapping
Flood modelling
Flood modelling is a tool used to model flood hazard and the effects on humans and the physical environment.
Flood hazard mapping
A flood hazard map is essential for flood management because it allows you to understand and visualize the areas that are most vulnerable to flooding under different scenarios. As an example, in Bangladesh, where nearly 80% of the population lives in low-lying floodplains, such a map aids in identifying areas prone to recurring or severe flooding caused by seasonal monsoon rains and river overflows. Hazard maps provide critical insights into disaster preparedness and planning by taking into account factors such as elevation, landform, slope, population density, and proximity to rivers and settlements. They assist local and national authorities in prioritizing high-risk zones, implementing preventive measures, and making informed resource allocation decisions to minimize loss of life, damage to infrastructure, and economic disruption during flood events.
Flood shelter suitability mapping
Knowing the flood risk is not always enough; a flood shelter suitability map is also helpful because it identifies the safest and most accessible locations for establishing emergency shelters. Nowadays in Bangladesh, the number of casualties from cyclones has reduced as many cyclone shelters have been established. In flood-prone areas of Bangladesh
Stakeholder engagement
Stakeholder engagement is a useful tool for flood risk management that allows enhanced public engagement for agreements to be reached on policy discussions.
Wetland Restoration
are effective for flood management strategies, particularly in coastal regions, because they are able to hold excess water that flows towards inland regions.
Costs
The costs of flood protection rise as more people and property are to be protected. The US FEMA, for example, estimates that for every $1.00 spent on mitigation, $4.00 is saved.
Examples by country
North America
Canada
An elaborate system of flood way defenses can be found in the Canadian province of Manitoba. The Red River flows northward from the United States, passing through the city of Winnipeg (where it meets the Assiniboine River) and into Lake Winnipeg. As is the case with all north-flowing rivers in the temperate zone of the Northern Hemisphere, snow melt in southern sections may cause river levels to rise before northern sections have had a chance to completely thaw. This can lead to devastating flooding, as occurred in Winnipeg during the spring of 1950. To protect the city from future floods, the Manitoba government undertook the construction of a massive system of diversions, dikes, and flood ways (including the Red River Floodway and the Portage Diversion). The system kept Winnipeg safe during the 1997 flood which devastated many communities upriver from Winnipeg, including Grand Forks, North Dakota and Ste. Agathe, Manitoba.
United States
In the United States, the U.S. Army Corps of Engineers is the lead flood control agency.[U.S. Army Corps of Engineers, Washington, DC. "Civil Works." Accessed 2014-01-24.] After Hurricane Sandy, New York City's Metropolitan Transportation Authority (MTA) initiated multiple flood barrier projects to protect the transit assets in Manhattan. In one case, the MTA's New York City Transit Authority (NYCT) sealed subway entrances in lower Manhattan using a deployable fabric cover system called Flex-Gate,
In the New Orleans Metropolitan Area, 35 percent of which sits below sea level, is protected by hundreds of miles of levees and flood gates. This system failed catastrophically, with numerous breaks, during Hurricane Katrina (2005) in the city proper and in eastern sections of the Metro Area, resulting in the inundation of approximately 50 percent of the metropolitan area, ranging from a few inches to twenty feet in coastal communities.
The Morganza Spillway provides a method of diverting water from the Mississippi River when a river flood threatens New Orleans, Baton Rouge and other major cities on the lower Mississippi. It is the largest of a system of spillways and floodways along the Mississippi. Completed in 1954, the spillway has been opened twice, in 1973 and in 2011.
In an act of successful flood prevention, the federal government offered to buy out flood-prone properties in the United States in order to prevent repeated disasters after the 1993 flood across the Midwest. Several communities accepted and the government, in partnership with the state, bought 25,000 properties which they converted into wetlands. These wetlands act as a sponge in storms and in 1995, when the floods returned, the government did not have to expend resources in those areas.[Ripley, Amanda (2006-08-28). "Floods, Tornadoes, Hurricanes, Wildfires, Earthquakes... Why We Don't Prepare." Time.]
Asia
In Kyoto, Japan, the Hata clan successfully controlled floods on the Katsura River in around 500 A.D and also constructed a sluice on the Kazuno River.
In China flood Diversion dam areas are rural areas that are deliberately flooded in emergencies in order to protect cities.[ "China blows up seventh dike to divert flooding." China Daily. 2003-07-07.]
The consequences of deforestation and changing land use on the risk and severity of flooding are subjects of discussion. In assessing the impacts of Himalayan deforestation on the Ganges-Brahmaputra Lowlands, it was found that forests would not have prevented or significantly reduced flooding in the case of an extreme weather event.
Many have proposed that loss of vegetation (deforestation) will lead to an increased risk of flooding. With natural forest cover the flood duration should decrease. Reducing the rate of deforestation should improve the incidents and severity of floods.
Africa
In Egypt, both the Aswan Low Dam (1902) and the Aswan High Dam (1976) have controlled various amounts of flooding along the Nile River.
Europe
France
Following the misery and destruction caused by the 1910 Great Flood of Paris, the French government built a series of reservoirs called (or Great Lakes) which helps remove pressure from the Seine during floods, especially the regular winter flooding.[See Jeffrey H. Jackson, Paris Under Water: How the City of Light Survived the Great Flood of 1910 (New York: Palgrave Macmillan, 2010).]
United Kingdom
London is protected from flooding by Thames Barrier, a huge mechanical barrier across the River Thames, which is raised when the water level reaches a certain point. This project has been operational since 1982 and was designed to protect against a surge of water such as the North Sea flood of 1953.
In 2023 it was found that over 4,000 flood defence schemes in England were 'almost useless' with many of them in areas hit by Storm Babet.
Russia
The Saint Petersburg Dam was completed in 2008 to protect Saint Petersburg from . It also has a main traffic function, as it completes a Beltway around Saint Petersburg. Eleven dams extend for and stand above water level.
The Netherlands
The Netherlands has one of the best flood control systems in the world, notably through its construction of dykes. The country faces high flooding risk due to the country's low-lying landscapes.
New ways to deal with water are constantly being developed and tested, such as the underground storage of water, storing water in reservoirs in large parking garages or on playgrounds.[
Palca, Joe (2008-01-28). "Dutch Architects Plan for a Floating Future." National Public Radio, Washington, DC.] Several approaches, from high-tech sensors detecting imminent levee failure to Thames Barrier closing an entire river, are being developed or used around the world. Regular maintenance of hydraulic structures, however, is another crucial part of flood control.
Oceania
Flooding is the greatest natural hazard in New Zealand,
See also
External links
