Flood Management Strategies
Flooding can severely impact on the lives, and businesses of people. On top of, the social and economic impacts, flooding can have severe environmental consequences, which affect humans, animals and all other living organisms. Floods can destroy habitats, erode the land, lead to food shortages, and, to the contamination of water supplies to name but a few. So it is not surprising that people look for ways to prevent floods from happening, this is where flood management strategies come in. Flood management strategies are put in place to protect, homes, businesses and the environment. Unfortunately, flood management is expensive, and due to this there isn't enough money to protect everywhere, deciding where flood defences should be built/placed is done using cost-benefit analysis. It is important that money is spent wisely, and as many people and businesses as possible benefit from flood management schemes, this means that large residential and large industrial areas are more likely to be protected from flooding, than, small residential areas or farmland.
There are numerous ways of managing floods which include Hard Engineering and Soft Engineering
Hard Engineering Defences - man-made structures that reduce flooding
General disadvantages include:
The construction of hard engineering defences requires a lot of technical skill and they are very expensive to build. This means that poorer countries are less likely to be able to afford hard engineering defences.
Hard engineering defences reduce how often floods happen. However, if something goes wrong, for example a dam breaks, the resulting flood can have far greater consequences. This is because when a dam breaks it releases a huge amount of water very rapidly which will result in the surrounding area very quickly becoming flooded.
Hard engineering defences lead to the disruption of natural processes, for example, when a dam is in place, the deposition of fertile silt on the floodplain during a low level flood no longer happens.
Hard engineering defences such as dams tend to stand out, some people feel they are a blot on the landscape (they're ugly) and can spoil a persons enjoyment of the area.
Hard Engineering Defences - man-made structures that reduce flooding
General disadvantages include:
The construction of hard engineering defences requires a lot of technical skill and they are very expensive to build. This means that poorer countries are less likely to be able to afford hard engineering defences.
Hard engineering defences reduce how often floods happen. However, if something goes wrong, for example a dam breaks, the resulting flood can have far greater consequences. This is because when a dam breaks it releases a huge amount of water very rapidly which will result in the surrounding area very quickly becoming flooded.
Hard engineering defences lead to the disruption of natural processes, for example, when a dam is in place, the deposition of fertile silt on the floodplain during a low level flood no longer happens.
Hard engineering defences such as dams tend to stand out, some people feel they are a blot on the landscape (they're ugly) and can spoil a persons enjoyment of the area.
Common types of hard engineering defences:
Dams
A dam is a massive wall that is constructed across the path of a river. A reservoir forms behind the dam, floodwater collects in the reservoir preventing flooding downstream. The release of the water from the dam happens slowly over the following months.
Advantages
Dams can be used to generate electricity using turbines that convert the water flowing through them into power.
The surrounding land can be irrigated by diverting water that is being released from the dam.
The reservoir can be used for leisure activities, such as sailing and windsurfing.
Disadvantages
Expensive to build and maintain.
People, businesses and animals can be displaced when the land surrounding a dam is flooded during its construction.
Dams can affect wildlife by interfering with the natural course of the river. One example is how dams prevent Salmon swimming upstream to reach their spawning grounds, although, schemes are now being introduced, to help Salmon and other species pass through dams and other man-made obstacles along the river channel.
Dams trap sediment which can 1) lead to the dam failing and, 2) result in increased erosion downstream due to a reduction in the deposition of sediment.
Channel Straightening
Channel straightening is where meanders are taken out of a river by building a cut-through. This straightens out the channel and increases the flow rate of the river, the result is water drains downstream faster and no longer breaches the banks which prevents flooding in the area.
Advantages
The stretch if river that as been straightened is shorter, reducing the time it takes to navigate it.
Disadvantages
Channel straightening can result in other areas downstream that did not previously flood, flooding. This is the result of floodwater moving faster downstream.
The increased speed of the river increases the amount of erosion downstream.
By altering the natural course of the river, wildlife habitats are disturbed.
Levees
Levees are embankments that have been constructed to build up the banks of the river. This results in the river being able to carry more water and reduces the frequency of flooding.
Advantages
The construction of levees mean that floodplains can be used as they are less likely to flood, this frees up additional land for building purposes.
Disadvantages
Levees are expensive to construct
If the levee is breached it could result in a severe flood
Diversion Spillways
Diversion spillways are channels that divert water away from the river channel, this reduces discharge and the risk of flooding. The water is usually diverted around important areas, protecting them from the consequences of flooding. The water is either channelled so that it re-joins the same river further upstream or directly into a different river. Some diversion spillways have gates which are used to control the release of water from them.
Disadvantages
Due to an increase in discharge there is an increased risk of flooding downstream of the point where the diverted water re-joins the river (or another river).
In extreme conditions the diversion spillway may not be able to cope with the amount of water entering the channel, this can lead to the surrounding area (which has doesn't normally flood) being flooded causing even greater problems in the area.
Dams
A dam is a massive wall that is constructed across the path of a river. A reservoir forms behind the dam, floodwater collects in the reservoir preventing flooding downstream. The release of the water from the dam happens slowly over the following months.
Advantages
Dams can be used to generate electricity using turbines that convert the water flowing through them into power.
The surrounding land can be irrigated by diverting water that is being released from the dam.
The reservoir can be used for leisure activities, such as sailing and windsurfing.
Disadvantages
Expensive to build and maintain.
People, businesses and animals can be displaced when the land surrounding a dam is flooded during its construction.
Dams can affect wildlife by interfering with the natural course of the river. One example is how dams prevent Salmon swimming upstream to reach their spawning grounds, although, schemes are now being introduced, to help Salmon and other species pass through dams and other man-made obstacles along the river channel.
Dams trap sediment which can 1) lead to the dam failing and, 2) result in increased erosion downstream due to a reduction in the deposition of sediment.
Channel Straightening
Channel straightening is where meanders are taken out of a river by building a cut-through. This straightens out the channel and increases the flow rate of the river, the result is water drains downstream faster and no longer breaches the banks which prevents flooding in the area.
Advantages
The stretch if river that as been straightened is shorter, reducing the time it takes to navigate it.
Disadvantages
Channel straightening can result in other areas downstream that did not previously flood, flooding. This is the result of floodwater moving faster downstream.
The increased speed of the river increases the amount of erosion downstream.
By altering the natural course of the river, wildlife habitats are disturbed.
Levees
Levees are embankments that have been constructed to build up the banks of the river. This results in the river being able to carry more water and reduces the frequency of flooding.
Advantages
The construction of levees mean that floodplains can be used as they are less likely to flood, this frees up additional land for building purposes.
Disadvantages
Levees are expensive to construct
If the levee is breached it could result in a severe flood
Diversion Spillways
Diversion spillways are channels that divert water away from the river channel, this reduces discharge and the risk of flooding. The water is usually diverted around important areas, protecting them from the consequences of flooding. The water is either channelled so that it re-joins the same river further upstream or directly into a different river. Some diversion spillways have gates which are used to control the release of water from them.
Disadvantages
Due to an increase in discharge there is an increased risk of flooding downstream of the point where the diverted water re-joins the river (or another river).
In extreme conditions the diversion spillway may not be able to cope with the amount of water entering the channel, this can lead to the surrounding area (which has doesn't normally flood) being flooded causing even greater problems in the area.
Soft Engineering Defences - man-made defences that try to work with the drainage basin processes and not against them
General advantages:
Soft engineering defences are cheaper to build and maintain than hard engineering defences, this makes them more accessible to poorer countries. Soft engineering defences reduce the risk of flooding and unexpected disasters. Soft engineering defences are considered by many to be more attractive and less likely than hard engineering defences to spoil our enjoyment of the landscape. They can also improve leisure opportunities such as fishing, football and bird watching.
General advantages:
Soft engineering defences are cheaper to build and maintain than hard engineering defences, this makes them more accessible to poorer countries. Soft engineering defences reduce the risk of flooding and unexpected disasters. Soft engineering defences are considered by many to be more attractive and less likely than hard engineering defences to spoil our enjoyment of the landscape. They can also improve leisure opportunities such as fishing, football and bird watching.
Common types of Soft Engineering Defences:
Land use management
Restricts what flood plains can be used for. Planning restrictions prevent roads and buildings from being constructed on flood plains, and use of the land is restricted to things such as, parks, playing fields and allotments. Because the surface of the flood plain remains permeable, water can freely infiltrate that ground which reduces runoff, discharge and flooding.
Advantages
These restrictions mean the impact of flooding is reduced, because no new buildings or roads are built on the flood plain, which means buildings and roads less likely to be damaged in a flood.
There are more opportunities for parks, playing fields, and allotments to be built, this provides recreational opportunities and can lead to improvements in peoples health and quality of life.
Disadvantages
It can lead to a shortage in housing due to the restrictions placed on where houses can be built.
In areas that have previously been urbanised this method of flood defence is not possible.
Wetland and river bank conservation
Conserving or re-establishing wetlands gives an area, natural protection from future floods. Wetlands naturally store floodwater, slow it's progress down and act as a natural flood defence. Furthermore, by planting trees and shrubs along the banks of a river, interception and lag time are increased, which in turn helps to reduce discharge and the risk of flooding.
Advantages
Soil is protected against erosion by the vegetation
The (re)introduction of vegetation leads to greater species diversity in the area due to a greater availability of habitats.
Disadvantages
There is a reduction in the amount of land available for farming
River restoration
River restoration is when a river is returned to it's natural state, by removing man-made structures such as levees along it's course. The result of removing a levee is, the river can once again flow naturally onto the flood plain, this reduces discharge and flooding downstream.
Advantages
River restoration reduces the amount of river maintenance needed.
Helps wildlife by improving habitats and increasing habitat availability.
Disadvantages
River restoration can increase the risk of local flooding.
Alteration of urban surfaces
By building pavements out of porous materials or incorporating soakaways in our pavements and roadways, infiltration can be increased and rapid surface runoff reduced. This results in an increased lag time, and reduced discharge and risk of flooding.
Advantages
Pollution is less likely to reach the river channel because pollutants are filtered out as they pass through the soil.
Disadvantages
The alteration of urban surfaces, through the use of porous materials or soakaways is expensive, making them less likely to be used.
Weather forecasts and flood warnings
The impact of flooding through severe weather can also be reduced through early warning systems. The environment agency warns people who live in flood prone areas of impending floods. They monitor weather forecasts, river discharge and rainfall in order to predict impending floods and determine when a warning needs to be sent out. This advance warning gives people the chance to protect their property and evacuate the area before a flood happens. The advance warning not only saves lives, it can also help to reduce the financial impacts of flooding and help the emergency services to prepare for a flood event.
Follow the link below to the environment agencies' flood warning page for the river Trent and it's tributaries.
Use the links on the page to investigate current flood warnings in the area. Use the tabs to explore other issues associated with flooding and to research current flood warnings in other areas.
http://apps.environment-agency.gov.uk/flood/34681.aspx?area=034WAF414
Disadvantages
There isn't always enough time to warn people in advance such as in the case of a flash flood.
If flood warnings have been inaccurate in the past people may feel they can't trust the information and choose to ignore the warning.
Not everyone is able to access the communications network.
Soft Engineering defences versus Hard Engineering defences
Land use management
Restricts what flood plains can be used for. Planning restrictions prevent roads and buildings from being constructed on flood plains, and use of the land is restricted to things such as, parks, playing fields and allotments. Because the surface of the flood plain remains permeable, water can freely infiltrate that ground which reduces runoff, discharge and flooding.
Advantages
These restrictions mean the impact of flooding is reduced, because no new buildings or roads are built on the flood plain, which means buildings and roads less likely to be damaged in a flood.
There are more opportunities for parks, playing fields, and allotments to be built, this provides recreational opportunities and can lead to improvements in peoples health and quality of life.
Disadvantages
It can lead to a shortage in housing due to the restrictions placed on where houses can be built.
In areas that have previously been urbanised this method of flood defence is not possible.
Wetland and river bank conservation
Conserving or re-establishing wetlands gives an area, natural protection from future floods. Wetlands naturally store floodwater, slow it's progress down and act as a natural flood defence. Furthermore, by planting trees and shrubs along the banks of a river, interception and lag time are increased, which in turn helps to reduce discharge and the risk of flooding.
Advantages
Soil is protected against erosion by the vegetation
The (re)introduction of vegetation leads to greater species diversity in the area due to a greater availability of habitats.
Disadvantages
There is a reduction in the amount of land available for farming
River restoration
River restoration is when a river is returned to it's natural state, by removing man-made structures such as levees along it's course. The result of removing a levee is, the river can once again flow naturally onto the flood plain, this reduces discharge and flooding downstream.
Advantages
River restoration reduces the amount of river maintenance needed.
Helps wildlife by improving habitats and increasing habitat availability.
Disadvantages
River restoration can increase the risk of local flooding.
Alteration of urban surfaces
By building pavements out of porous materials or incorporating soakaways in our pavements and roadways, infiltration can be increased and rapid surface runoff reduced. This results in an increased lag time, and reduced discharge and risk of flooding.
Advantages
Pollution is less likely to reach the river channel because pollutants are filtered out as they pass through the soil.
Disadvantages
The alteration of urban surfaces, through the use of porous materials or soakaways is expensive, making them less likely to be used.
Weather forecasts and flood warnings
The impact of flooding through severe weather can also be reduced through early warning systems. The environment agency warns people who live in flood prone areas of impending floods. They monitor weather forecasts, river discharge and rainfall in order to predict impending floods and determine when a warning needs to be sent out. This advance warning gives people the chance to protect their property and evacuate the area before a flood happens. The advance warning not only saves lives, it can also help to reduce the financial impacts of flooding and help the emergency services to prepare for a flood event.
Follow the link below to the environment agencies' flood warning page for the river Trent and it's tributaries.
Use the links on the page to investigate current flood warnings in the area. Use the tabs to explore other issues associated with flooding and to research current flood warnings in other areas.
http://apps.environment-agency.gov.uk/flood/34681.aspx?area=034WAF414
Disadvantages
There isn't always enough time to warn people in advance such as in the case of a flash flood.
If flood warnings have been inaccurate in the past people may feel they can't trust the information and choose to ignore the warning.
Not everyone is able to access the communications network.
Soft Engineering defences versus Hard Engineering defences
Hard Engineering Defences
Often expensive - poorer countries are less likely to be able to afford hard engineering defences Disrupts natural processes - e.g. diverts the natural course of the river |
Soft Engineering defences
Cheaper to build and maintain than hard engineering defences - important for poorer countries Works with natural processes - e.g. uses flood plains as natural flood defences More sustainable - lower economic and environmental impact |
Sources
AQA (2012): AS & A2 Geography complete revision and practice all in one book
Askville by Amazon
environmentagency.gov/flood
Office of response and restoration website
pavingexperts.com
round the world in 30 days website
watershed events typad.com
AQA (2012): AS & A2 Geography complete revision and practice all in one book
Askville by Amazon
environmentagency.gov/flood
Office of response and restoration website
pavingexperts.com
round the world in 30 days website
watershed events typad.com