Chapter 2 4.8 Flashcards
Pros/cons of hard engineering to manage flood risk
Method:
Flood walls pros:
Fairly cheap e.g one off costs to build it costs £4.4 million
Useful for city centres where space is limited
Flood walls cons:
They disperse quickly this can increase the flood risk downstream
Levees pros:
Expensive but can they can allow people who live beside the river with reduced fear of flooding.
Levees cons:
Can fail by overtopping ( water rises above the levee ), slumping or erosion
They can increase the flood risk downstream
They can cost £1 million depending on the materials used
Dredging pros:
It protects built up areas but could cause flooding downstream
Dredging cons:
Speeding up flow increases flood risk downstream
Costs up to £50,000 per time done
Needs to be dredged every year as the channel fills with sediment each time it rains heavily
Concrete is expensive to build but cheap to maintain
Pros/cons of soft engineering methods to manage flood risk
Flood plain retention pros:
Increased ability to store flood water
Floods areas are reduced e.g. in 2007 despite heavy rains there was less flooding than the previous year
The only flooding in Darlington that year was caused by back logged water in drains, not by the river
River channel restoration pros:
Improved ecology with a 30% increase in birds and insects
In a survey people said they liked the restored river more, the number was 82%!!
Afforestation pros:
Natural way of reducing flood risk which improves the view in an area. It increases natural habitats for wildlife too. There is low maintenance required.
Afforestation cons:
Trees (if bought largely grown are expensive, and if they are saplings (young) they take a long time before they are effective.
What are flood walls
Build a high wall alongside a river to increase its capacity.
What are levees?
Like flood walls, building levees increases the capacity of the river- and are normally built at a distance from the river which increases capacity between them
What is dredging and flood relief channel
Dredging the river to increase channel capacity or line it with concrete to speed up river flow. Flood relief channels are used to create extra channels to divert excess flood water from city centres.
What is the flood plain retention
The level of flood plains is lowered and their surfaces restored to shrubs or grassland so they can adsorb more water over a period than that area would have otherwise absorbed.
What is river channel restoration
Some meanders were rebuilt making the river longing and allowing more water to flow in it, banks were also lowered to flood grassland instead of a town. Concrete was replaced with sediment.
What is afforestation
Planting trees in the upper course of the river intercepts large volumes of water and allows for more evapotranspiration. Surface run-off is reduced as a result and the flood risk is reduced.
Compare flood plain retention and flood walls
I think that flood plain retention gives flood plains the ability to store flood water. An example of this is flooding was reduced in 2007, despite heavy rains. Compared with flood walls, which are not as useful in rural areas as flood plain retention schemes are.
Why is flood risk increasing?
Flood risk is increasing due to a number of factors including: air temperature rising because warmer air can hold more water meaning more energy, warm air holds more moisture, climate change because human emissions of greenhouse gasses are to blame such as carbon dioxide from fossil fuel burning.
