Flood Management Strategies Flashcards
How do we chose which places to protect?
Isn’t enough money to protect everywhere, use a cost benefit analysis
Large settlements and import any industrial sites are more likely to be protected than small settlements or farmland
What are the two forms of flood management?
Hard engineering and soft engineering
Define hard engineering
Defences are man made structures that reduce flooding
What are the disadvantages of hard engineering?
They’re expensive to build and maintain, need technical skill, poorer countries can’t afford these flood defences
Floods happen less often but can be more hazardous if they do happen, e.g. if dam breaks then a huge amount of water is released
Natural processes are disrupted, e.g. crops don’t get fertile silt from river sediment during low-level flooding
Can be ugly
What are four hard engineering flood management strategies?
Dams
Channel straightening
Levees
Diversion spillways
Explain a dam
Dams are huge walls built across rivers, reservoir is formed behind the dam melody water is caught by the dam, prevents flooding downstream, Water is released as steady flow through out the year
Benefits of a dam
Turbines can be built into the dams, generate electricity
Steady water release allows irrigation of land below the dam through out the year
People can use the reservoir for recreational activities
What are the disadvantages of a dam?
Very expensive
Land is flooded when a reservoir is created, often destroys farmland and forces people to move elsewhere
Affect wildlife e.g. can prevent salmon migration upstream
They trap sediment normally carried in rivers, can cause dam to fail, increased erosion downstream as there’s less protective sediment being deposited
Explain channel straightening
Where meanders are removed by building artificial cut-throughs, makes the water flow faster, reduces flooding because water drains downstream more quickly and doesn’t build up to a point where the river channel can’t contain it anymore.
Benefits of channel straightening
Takes less time to navigate the river because it has been made shorter
Disadvantages of channel straightening
Flooding may happen downstream instead as flood water carried there faster
More erosion occurs downstream because the river flows faster
Alternating river channels disturbs wildlife habits
Explain levees
Are embankments built along rivers, river can hold more water without overflowing and so it floods less often
Advantage of a levee
They allow the flood plain to be built upon
Disadvantages of levees
They’re quite expensive
There’s a risk of severe flooding if the levees are breached
Explain diversion spillways
Channels that take water elsewhere if the water level in the river is too high. Water is normally diverted around an important area or to another river.
Advantages of diversion spillways
Prevent flooding because river discharge is reduced
Spillways often have gates that can be opened, so release of water can be controlled
Disadvantages of diversion spillways
An increase in discharge when the diverted water joins another river could cause flooding below that point
If spillways are overwhelmed, water will flood areas not used to flooding, could cause even bigger problems
What is the aim of flood management?
To protect homes, businesses and the environment from flooding
Define soft engineering
Defences use knowledge of the whole river basin and its processes to try to work with nature
What are the advantages of soft engineering strategies?
They’re cheaper to maintain than hard engineering strategies
Flooding is more predictable, reducing the risk of an unexpected disaster
Can improve opportunities for recreation, such as fishing
Think they’re more attractive than hard engineering schemes
What are the four soft engineering schemes?
Land use management
Wetland and river bank conservation
River restoration
Alteration of urban surfaces
Explain land use management
Planning restrictions prevent buildings or roads being constructed in the flood plain.
Use of the flood plain is restricted to things like playing fields, allotments or parks. More water can infiltrate so there’s less surface runoff which reduces discharge.
What are the benefits of land use management?
There are no new buildings or roads on the floodplain to be damaged, impact of any flooding is reduced
Provides recreational opportunities e.g. football fields
What are the disadvantages of land use management?
Restricts development, a big problem when there’s a shortage of housing
Can’t be used in areas that are already urbanised
Explain wetland and river bank conservation
Wetlands store flood water and also slow it down, reduces flooding downstream.
Conserving or re-establishing wet,ands gives natural protection from flooding. Planting trees and shrubs along the river bank increases interception and lag time, reduces discharge.
What are the benefits of wetlands and river bank conservation?
Vegetation protects the surface soil from erosion
The vegetation provides habitats for wildlife
What are the disadvantages of wetland and river bank conservation?
Less land is available for farming
Explain river restoration
Involves making the river more natural e.g. by removing man-made levees.
Flood plain can then flood naturally, as water spreads out over the flood plain the rivers discharge is reduced
What are the benefits of river restoration?
Little maintenance is needed, rivers left in its natural state
The river provides a better habitat for wildlife
What are the disadvantages of river restoration?
Local flood risk increases, esp if nothing is done to prevent major flooding
Explain alteration of urban surfaces
Building porous pavements or soakaways increases infiktration, reduces rapid surface runoff to the river channel. Reduces lag time, reduces discharge.
What are the benefits of alteration of urban surfaces?
Any pollutants in the water are filtered out by the soil before the water reaches the channel
What are the disadvantages of alteration of urban surfaces?
It’s expensive
What is the most sustainable food management strategy? Why?
Soft engineering LOWER ECONOMIC COST AND ENVIRONMENTAL IMPACT
HE is often more expensive and disrupts natural processes, SE tends to be cheaper and require less time and money to maintain than HE.
SE is designed to integrate with the natural environment and it creates areas like wetlands, important habitats for wildlife.
