By: Salam Gunakanta Singh,
Environmentalist
Natural Disasters – Floods
If you thought that floods are natural disasters that happened only in poorer continents like Africa and Asia, then you are wrong. First, not all floods are caused by nature. They are man-made too. And second, even countries like the USA and the UK get floods that cause huge losses to life and property. To understand what causes floods and how man’s activities affect floods, visit the links mentioned below.
For a simple and scientific explanation of floods and different types of floods, visit this link. The language is simple and the concepts are clearly explained in this site. See the diagrams to understand how the landscape changes when floods occur.
Causes of floods
To understand how floods are caused, the extent to which they can be considered as “acts of God” and how the activities of man can make floods more or less severe, read this comprehensive guide here.
It is written mainly for insurance companies, builders and other professionals and talks mostly of flooding in UK. But it is very informative as the basic facts remain the same- the change in landscape, land use, how the size of the river basin and the flood plain affects the severity of floods, and how we can prepare for floods in a flood prone area.
1998: A year of floods
One of the nature’s most turbulent years was 1998. Floods wreaked havoc in North America, South America, Asia and Europe. Though the El Nino and La Nina were thought to be responsible for these floods, scientists have now found out that these factors combined with global warming caused by pollution and made the disasters more severe.
Deforestation and global warming are cited as two of the main man-made causes that led to such a disastrous year with loss of lives and huge damage. Read these reports from BBC network on some of the worst floods and the devastating effect of Hurricane Mitch – all testimonies to the result of human activity interacting with natural phenomena.
Are man-made floods possible?
A debate around the world is that nature is to blame for natural hazards while one section says that man causes or triggers these hazards by deforestation and pollution. In China, a flood affected the lives of 250 million people and caused large scale devastation and the El Nino was cited as the main cause.
But after some analysis, it has been found that it was caused by large scale deforestation leading to loose soil and therefore huge floods. Read this article to know more about this debate.
How are floods caused by man? How do man-made changes in a river basin affect floods? In Washington, floods are caused by man-made actions. The rapid urbanization of Washington has led to more concrete surfaces that seal the surface and do not allow water to seep in.
Dikes can help contain the water but they also cut off the river from the floodplain. The floodplain helps to retain some of the floodwater but cutting the river off from it means that this natural storage is gone. The consequent pressure on the environment leads to such disasters.
What causes Floods?
Flooding occurs most commonly from heavy rainfall when natural watercourses do not have the capacity to convey excess water. However, floods are not always caused by heavy rainfall. They can result from other phenomena, particularly in coastal areas where inundation can be caused by a storm surge associated with a tropical cyclone, a tsunami or a high tide coinciding with higher than normal river levels. Dam failure, triggered for example by an earthquake, will result in flooding of the downstream area, even in dry weather conditions.
Other factors which may contribute to flooding include:
• volume, spatial distribution, intensity and duration of rainfall over a catchment;
• the capacity of the watercourse or stream network to convey runoff;
• catchment and weather conditions prior to a rainfall event;
• ground cover;
• topography; and
• tidal influences.
Types of Flood
Three Common Types of Flood Explained
One of the keys to understanding flood risk is understanding the nuances of the type (or types) of flood you face. Why? A flood’s a flood, right? Wrong. There are several different kinds of flood, and each one bears a different impact in terms of how it occurs, the damage it causes, and how it is forecasted. Here’s a crash course on three common types of flood to help you better assess your risk.
Coastal (Surge Flood)
A coastal flood, as the name suggests, occurs in areas that lie on the coast of a sea, ocean, or other large body of open water. It is typically the result of extreme tidal conditions caused by severe weather. Storm surge — produced when high winds from hurricanes and other storms push water onshore — is the leading cause of coastal flooding and often the greatest threat associated with a tropical storm. In this type of flood, water overwhelms low-lying land and often causes devastating loss of life and property.
Coastal flooding is categorized in three levels:
• Minor: A slight amount of beach erosion will occur but no major damage is expected.
• Moderate: A fair amount of beach erosion will occur as well as damage to some homes and businesses.
• Major: Serious threat to life and property. Large-scale beach erosion will occur, numerous roads will be flooded, and many structures will be damaged. Citizens should review safety precautions and prepare to evacuate if necessary.
The severity of a coastal flood is determined by several factors, including the strength, size, speed, and direction of the storm. The onshore and offshore topography also plays an important role. To determine the probability and magnitude of a storm surge, coastal flood models consider this information in addition to data from historical storms that have affected the area, as well as the density of nearby development.Fluvial (River Flood)
Fluvial or riverside flooding, occurs when excessive rainfall over an extended period of time causes a river to exceed its capacity. It can also be caused by heavy snow melt and ice jams. The damage from a river flood can be widespread as the overflow affects smaller rivers downstream, often causing dams and dikes to break and swamp nearby areas.
There are two main types of riverside flooding:
• Overbank flooding occurs when water rises overflows over the edges of a river or stream. This is the most common and can occur in any size channel — from small streams to huge rivers.
• Flash flooding is characterized by an intense, high velocity torrent of water that occurs in an existing river channel with little to no notice. Flash floods are very dangerous and destructive not only because of the force of the water, but also the hurtling debris that is often swept up in the flow.
The severity of a river flood is determined by the amount of precipitation in an area, how long it takes for precipitation to accumulate, previous saturation of local soils, and the terrain surrounding the river system. In flatter areas, floodwater tends to rise more slowly and be shallower, and it often remains for days. In hilly or mountainous areas, floods can occur within minutes after a heavy rain. To determine the probability of river flooding, models consider past precipitation, forecasted precipitation, current river levels, and temperatures.
Pluvial (Surface Flood)
A pluvial, or surface water flood, is caused when heavy rainfall creates a flood event independent of an overflowing water body. One of the most common misconceptions about flood risk is that one must be located near a body of water to be at risk. Pluvial flooding debunks that myth, as it can happen in any urban area — even higher elevation areas that lie above coastal and river floodplains.
There are two common types of pluvial flooding:
• Intense rain saturates an urban drainage system. The system becomes overwhelmed and water flows out into streets and nearby structures.
• Run-off or flowing water from rain falling on hillsides that are unable to absorb the water. Hillsides with recent forest fires are notorious sources of pluvial floods, as are suburban communities on hillsides.
Pluvial flooding often occurs in combination with coastal and fluvial flooding, and although typically only a few centimetres deep, a pluvial flood can cause significant property damage.
Looking Ahead
Climate change models predict that severe weather will continue to intensify in the decades to come. At the same time, the world population continues to grow, bringing an increase in urban development. Therefore increased awareness of flood risk, along with better information and tools to help assess it, is critical to prevent devastating loss of life and property worldwide.
What are the consequences of floods?
Floods impact on both individuals and communities, and have social, economic, and environmental consequences. The consequences of floods, both negative and positive, vary greatly depending on the location and extent of flooding, and the vulnerability and value of the natural and constructed environments they affect.
The consequences of floods, both negative and positive, vary greatly depending on their location, duration, depth and speed, as well as the vulnerability and value of the affected natural and constructed environments. Floods impact both individuals and communities, and have social, economic, and environmental consequences
Floods have large social consequences for communities and individuals
As most people are well aware, the immediate impacts of flooding include loss of human life, damage to property, destruction of crops, loss of livestock, and deterioration of health conditions owing to waterborne diseases. As communication links and infrastructure such as power plants, roads and bridges are damaged and disrupted, some economic activities may come to a standstill, people are forced to leave their homes and normal life is disrupted.
Similarly, disruption to industry can lead to loss of livelihoods. Damage to infrastructure also causes long-term impacts, such as disruptions to supplies of clean water, wastewater treatment, electricity, transport, communication, education and health care. Loss of livelihoods, reduction in purchasing power and loss of land value in the floodplains can leave communities economically vulnerable.
Floods can also traumatise victims and their families for long periods of time. The loss of loved ones has deep impacts, especially on children. Displacement from one’s home, loss of property and disruption to business and social affairs can cause continuing stress. For some people the psychological impacts can be long lasting.
Flooding in key agricultural production areas can lead to widespread damage to crops and fencing and loss of livestock. Crop losses through rain damage, waterlogged soils, and delays in harvesting are further intensified by transport problems due to flooded roads and damaged infrastructure. The flow-on effects of reduced agricultural production can often impact well outside the production area as food prices increase due to shortages in supply. On the other hand, flood events can result in long-term benefits to agricultural production by recharging water resource storages, especially in drier, inland areas, and by rejuvenating soil fertility by silt deposition.
Damage to public infrastructure affects a far greater proportion of the population than those whose homes or businesses are directly inundated by the flood. In particular, flood damage to roads, rail networks and key transport hubs, such as shipping ports, can have significant impacts on regional and national economies.
Short-term downturns in regional tourism are often experienced after a flooding event. While the impact on tourism infrastructure and the time needed to return to full operating capacity may be minimal, images of flood affected areas often lead to cancellations in bookings and a significant reduction in tourist numbers.
Flooding of urban areas can result in significant damage to private property, including homes and businesses. Losses occur due to damage to both the structure and contents of buildings. Insurance of the structure and its contents against flooding can reduce the impacts of floods on individuals or companies.
Floods have significant consequences for the environment
In many natural systems, floods play an important role in maintaining key ecosystem functions and biodiversity. They link the river with the land surrounding it, recharge groundwater systems, fill wetlands, increase the connectivity between aquatic habitats, and move both sediment and nutrients around the landscape, and into the marine environment. For many species, floods trigger breeding events, migration, and dispersal. These natural systems are resilient to the effects of all but the largest floods.
The environmental benefits of flooding can also help the economy through things such as increased fish production, recharge of groundwater resources, and maintenance of recreational environments.
Areas that have been highly modified by human activity tend to suffer more deleterious effects from flooding. Floods tend to further degrade already degraded systems. Removal of vegetation in and around rivers, increased channel size, dams, levee bank and catchment clearing all work to degrade the hill-slopes, rivers and floodplains, and increase the erosion and transfer of both sediment and nutrients.
While cycling of sediments and nutrients is essential to a healthy system, too much sediment and nutrient entering a waterway has negative impacts on downstream water quality. Other negative effects include loss of habitat, dispersal of weed species, the release of pollutants, lower fish production, loss of wetlands function, and loss of recreational areas.
Many of our coastal resources, including fish and other forms of marine production, are dependent on the nutrients supplied from the land during floods. The negative effects of floodwaters on coastal marine environments are mainly due to the introduction of excess sediment and nutrients, and pollutants such as chemicals, heavy metals and debris. These can degrade aquatic habitats, lower water quality, reduce coastal production, and contaminate coastal food resources.
10 measures that must be taken to prevent more flooding in the future
Industry experts have warned that the economic cost of storms could hit £6bn
1. Introduce better flood warning systems
The UK must “improve our flood warning systems”, giving people more time to take action during flooding, potentially saving lives, the deputy chief executive of the Environment Agency, David Rooke, said. Advance warning and pre-planning can significantly reduce the impact from flooding.
2. Modify homes and businesses to help them withstand floods
The focus should be on “flood resilience” rather than defence schemes, according to Laurence Waterhouse, director of civil engineering flood consultancy Pell Frischmann. He advised concreting floors and replacing materials such as MDF and plasterboard with more robust alternatives. “We are going to have to live with flooding. It’s here to stay,” Mr Waterhouse said. “We need to be prepared.” His recommendations were echoed by Mr Rooke, who suggested waterproofing homes and businesses and moving electric sockets higher up the walls to increase resilience.
3. Construct buildings above flood levels
Britain should construct all new buildings one metre from the ground to prevent flood damage, the former president of the Institution of Civil Engineers has suggested. Professor David Balmforth, who specialises in flood risk management, said conventional defences had to be supplemented with more innovative methods to lower the risk of future disasters.
4. Tackle climate change
Climate change has contributed to a rise in extreme weather events, scientists believe. Earlier this month the leader of the Green Party, Natalie Bennett, welcomed the landmark Paris Agreement, whereby governments from 195 countries pledged to “pursue efforts” to limit the increase in global average temperatures to 1.5°C above pre-industrial levels. “It is now crucial that world leaders deliver on the promise of Paris,” Ms Bennett said. “The pressure is now on the British government to reverse its disastrous environmental policy-making.”
5. Increase spending on flood defences
Figures produced by the House of Commons library suggest that real terms spending on flood defences has fallen by 20 per cent since David Cameron came to power. Yesterday [MON] the Prime Minister rejected this allegation, insisting the amount being spent had risen. Mr Cameron promised to review spending on flood defences after chairing a conference call of the government’s emergency Cobra committee at the weekend.
6. Protect wetlands and introduce plant trees strategically
The creation of more wetlands – which can act as sponges, soaking up moisture – and wooded areas can slow down waters when rivers overflow. These areas are often destroyed to make room for agriculture and development, the WWF said. Halting deforestation and wetland drainage, reforesting upstream areas and restoring damaged wetlands could significantly reduce the impact of climate change on flooding, according to the conservation charity.
7. Restore rivers to their natural courses
Many river channels have been historically straightened to improve navigability. Remeandering straightened rivers by introducing their bends once more increases their length and can delay the flood flow and reduce the impact of the flooding downstream.
8. Introduce water storage areas
Following the severe flooding of 2009 a £5.6 million flood alleviation scheme was established in Thacka Beck, on the outskirts of Penrith, Cumbria. More than 675 metres of culverts underneath the streets of Penrith were replaced and a 76,000m³ flood storage reservoir – the equivalent of 30 Olympic sized swimming pools – was constructed upstream to hold back flood water. The risk of flooding from the beck was reduced from a 20 per cent chance in any given year to a one per cent chance, according to Cumbria Wildlife Trust.
9. Improve soil conditions
Inappropriate soil management, machinery and animal hooves can cause soil to become compacted so that instead of absorbing moisture, holding it and slowly letting it go, water runs off it immediately. Well drained soil can absorb huge quantities of rainwater, preventing it from running into rivers.
10. Put up more flood barriers
The Environment Agency uses a range of temporary or “demountable” defences in at-risk areas. These can be removed completely when waters recede. Temporary barriers can also be added to permanent flood defences, such as raised embankments, increasing the level of protection. “As the threat and frequency of flood risk increases, the use of passive flood defence has to be the only realistic long term solution,” Frank Kelly, CEO of UK Flood Barriers claimed earlier this month in Infrastructure Intelligence, a magazine for the infrastructure sector. Mr Kelly’s company was responsible for designing a self-activating flood barrier he said had proved to be “invaluable” in protecting properties close to the River Cocker.
