For populated coastlines, the risks associated with flooding are more significant than erosion. So you have to ask why on earth people would live in such an area? Understanding coastal flooding and the risks it presents helps us to come up with long term solutions. This way, tourism, trade and agriculture may be able to continue in a more sustainable way.
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Jetzt kostenlos anmeldenFor populated coastlines, the risks associated with flooding are more significant than erosion. So you have to ask why on earth people would live in such an area? Understanding coastal flooding and the risks it presents helps us to come up with long term solutions. This way, tourism, trade and agriculture may be able to continue in a more sustainable way.
Coastal flooding is a flood that occurs when (often low-lying) land that is usually dry is flooded with seawater. This happens because, for some reason, the sea level rises, and it will spill onto the land. This can happen by:
There are many possible causes of flooding on or near the coast. The major factors are:
Any low-lying coastal areas are vulnerable to coastal flooding as seawater can easily be swept inland. An example of areas vulnerable to coastal flooding is the mega-deltas of Asia.
The degree of erosion or subsidence can affect coastal flooding. Let's split these up.
Erosion is when materials are being worn away, for example, by waves and soft geology and transported elsewhere by natural forces such as wind or water. In other words, materials, such as earth or sand, are being taken away from their original place and deposited elsewhere. This erosion can lead to a weakening of the area or even remove it altogether.
An example is Holderness, in Yorkshire, England. Waves, storms and tidal surges constantly batter the coastline of Holderness. An estimated 2m every year erodes from Holderness; in other words, the sea is making that stretch of land smaller every year. This has led to a loss of property, farmland, damage and loss of infrastructure, and it poses a danger to tourism and coastal protection.
Subsidence is when underground material moves, causing the ground to sink. This can be due to natural causes, such as earthquakes or erosion, or it can be due to artificial causes, such as mineral resource mining or removing natural gas.
Low lying coastlines are subjected to natural subsidence through settling and compaction of recently deposited sediment. This subsidence is usually outpaced by fresh deposition. Human activities can also cause local subsidence through activities such as:
Major signs of subsidence (in buildings) are:
Coastal vegetation, including trees, intercepts the rainfall slowing down its movement, storing some whilst the rest evaporates. The vegetation also absorbs water from the soil allowing more significant infiltration into the ground, as a result reducing surface run-off.
When vegetation is removed, infiltration and interception are reduced and surface run-off increases. This to a greater risk of flooding as more water reaches the river channel.
The vegetation also stabilises existing sediment and traps new sediment, raising the height of the land above sea level. In addition, it absorbs wave energy, reducing wave impact and erosion, and reduces the distance waves travel onshore before their power is exhausted.
A lot of coastal flooding is a result of storm surges. Storm surges are short-term changes in sea levels caused by events such as tsunamis and cyclones. A storm surge is only measured by the water level that exceeds the normal tidal level, excluding waves.
Several meteorological factors contribute to a storm surge and its severity:
Fetch = "The area in which ocean waves are generated by the wind. It also refers to the length of the fetch area, measured in the direction of the wind" 3. Other terms are wind fetch and fetch length.
Storm surges are exacerbated through a variety of factors such as:
As bad as it may seem, we need to remember that these impacts will be short term. Sadly as a direct result of the storm, there will be some deaths and injuries through drowning or collapsing buildings.
Infrastructure such as roads, railways, ports, and airports will be flooded or destroyed. There will be damaged water pipes, electricity transmission lines and sewage systems; as a result, there is likely to be no power or water. Homes will be destroyed, and homes on marginally low lying land (slums and shantytowns) will be more vulnerable.
So what of the future with regards to storm surges and flood risk?
Records show an increase in the number of storms that form year on year. The average number of storms forming in the North Atlantic annually was 11; However, from 2000 to 2013, 16 storms formed per year, 8 of these were hurricane force. This increase relates to a rise in surface temperatures of the Atlantic ocean. As sea levels rise, damage from erosion and increasing storms will cause damage further and further inland.
Coastal flooding is something that can happen anywhere along a coastline. Especially the last few decades have proven to be significant as not only does it appear to happen more often, but coastal areas seem to attract more people, tourists and locals alike. The latter could potentially lead to more casualties when coastal flooding happens.
Coastal flooding does not only impact people directly, as in injured or dead, but it can also damage or destroy houses, businesses, infrastructure, and agriculture (including the death of livestock).
Here are some examples of coastal flooding.
As a low-lying country, the Netherlands has had its fair share of floods. One of the biggest floods was the North Sea flood of 1953. With the Netherlands being such a low-lying country, especially in the north of the country, it relies heavily on defences such as levees.
The storm surge hit the Netherlands, and on the night of 31 January 1953, things took a turn for the worst. The storm surge, combined with an unfavourable tide at the same time, caused a storm so powerful that water not only flooded over the barriers it also damaged and destroyed a number of them. The water flooded whole islands and coastal areas, killing 1,836 people in the Netherlands.
The storm also hit the north of West Flanders (Belgium), killing 28 people; the English counties Lincolnshire, Norfolk, Suffolk and Essex, killing 307 people; east Scotland, killing 19. Furthermore, approximately 220 people were killed at sea.
On 23 August 2005, Hurricane Katrina hit New Orleans, Louisiana (US), leaving behind a trail of destruction. The storm breached 53 levees, flooding much of the city, and it was later discovered that most of the levees broke due to fatal engineering flaws. Ultimately, 1,836 people died, and it caused a total of $125 billion worth of damage.
On 26 December 2004, one of the deadliest natural disasters in recorded history happened: an all-powerful tsunami, caused by an undersea earthquake, hit the countries and islands in the Indian Ocean.
There are 184,167 confirmed deaths, but it is estimated that approximately 227,898 people lost their lives. Other impacts are:
Almost 37,500.00 million (a fourth of the total population of around 150 million in 2011) people live in the coastal areas of Bangladesh, where most of the people are affected (directly or indirectly) by coastal floods, storm surges, and riverbank erosion, tropical cyclones etc. Bangladesh could lose up to 15% of its land by an increase in sea level of just one meter, large areas will be under the seawater, and people living in the coastal areas of Bangladesh would become refugees.
Bangladesh is especially vulnerable to the impact of flooding from tropical cyclones because:
There is not a lot that Bangladesh can do about the physical factors which make it prone to flooding; However, human actions are increasing the risk of coastal flooding through:
Three major cyclones have hit Bangladesh since 1970. The death toll from these has fallen over time through a better warning system, but most of the flooding was caused by a failure of the extensive embankment system forcing millions of people from their homes and farms. The 2007 cyclone, Sidr, had a storm surge of 3 meters with accompanying wind speeds of 20kmph (Max 1 minute sustained wind speed), causing a death toll of 15,000 and an estimated US 1.7 billion.
We know that sea levels are rising due to global warming, but how significant is this rise in terms of coastal flooding and erosion? Depressions and cyclones will continue to occur without global warming and sea level rises.
There is reason to believe that global warming will increase the risk to coasts. A summary of the IPCC, The UN's Intergovernmental Panel on Climate Change, 2014, stated that:
The risks highlighted above create an uncertain future, and we will need to mitigate and adapt against them.
Some predictions on the impacts of coastal flooding associated with global warming are more confident than others. Even in the IPCC summary, its forecasts ranged from high to low confidence. It also made a fascinating statement about coast change which might be blamed on global warming.
It is important to remember that coasts are a very complex system that can be affected by many factors. Therefore, blaming it on any 1 aspect will misrepresent the many factors that affect the level of risk on the coast.
There are two possible approaches to dealing with the risk.
Adaptation Adaptation is vital as making changes lessens the impact of flooding. This can be done by:
Mitigation
Reducing greenhouse emissions to limit global warming would mitigate sea level rise and cyclone intensity.
For future information on how coastal flooding could be managed, please see the following StudySmarter article.
Managing coastlines - Engineering Management Approaches and Governance Approaches.
References/sources:
Flooding can destroy coastal habitats such as coastal wetlands, estuaries and erode dune systems. These places are biologically diverse, and coastal flooding can cause significant biodiversity loss and potentially the extinction of a number of species. Agricultural land which is submerged by saltwater for a long period can result in the salination of the soil resulting in a loss of productivity for long periods. Food crops and forests can be ultimately killed off by the salination of soils or wiped out by the movement of floodwaters.
Coastal floods are when the sea floods the coast.
We can mitigate against it through the construction of barriers (sea walls), we can manage and restore natural habitats to reduce the waves energy (dunes and mangrove forests). But with predicted sea-level rise, I don't think we can prevent coastal flooding.
Storm surges, hurricanes, tropical storms, and rising sea levels as a result of climate change and tsunamis are all responsible for coastal flooding.
Coastal flooding can be reduced by adaptation to lessen the impacts of the flooding. For example, the construction of storm surge barriers, sea walls, and earth embankments and the management and restoration of natural obstacles, such as mangrove forests and dunes.
For populated coastlines, the risks associated with flooding are more significant than the risk of erosion. Why in that case do people live in such an area?
Because it is economically beneficial, for example, through tourism, as people love to visit the coast, through trade as deltas and estuaries make ideal ports, and as a result of agriculture, they have fertile soil.
The causes of flooding at the coast can be linked to what?
The height of land above sea level, the degree of erosion and subsidence, deforestation and vegetation removal and storm surges.
Give an example of a low lying coastal area vulnerable to coastal flooding?
The mega-deltas of Asia.
Erosion and subsidence at the coast are affected by human activities. Can you give any examples?
Through the drainage of saturated sediment/soil for agriculture, e.g. Fens of East Anglia. The weight of coastal towns and cities and built environment can also compress sediment, leading to subsidence, e.g. Venice. And through land reclaimed from the sea, the Netherlands.
How does the removal of vegetation affect coastal flooding?
Vegetation intercepts the rainfall, slowing down its movement by removing it. As a result, infiltration and interception are reduced and surface run-off increases. The vegetation also stabilises existing sediment and traps new sediment, raising the height of the land above sea level. In addition, it absorbs wave energy, reducing wave impact and erosion, and reduces the distance waves travel onshore before the energy is exhausted.
What is a storm surge?
They are a short term change in sea level caused by intense low-level pressure systems from depressions (a low-pressure weather system) and tropical cyclones (hurricanes, typhoons).
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