Topic 4, EQ5

Question 1

Why is river flood risk increasing?

Answer 1

Climate change will lead to more extreme weather events like Storm Desmond. These now have a likelihood of 1 in 85 days.
As global temperatures increase the warmer air has the capacity to hold a greater amount of water vapour.
The air temperature rose an average of 4.1°C.
The transition from El Niño to El Niña and vise versa can lead to unusual weather events.

Question 2

Compare how soft and hard engineering schemes work.

Answer 2

Soft Engineering: Using natural materials (usually cheaper) to precent flooding in an area but still retain an areas natural appearance.
Hard Engineering: Using harder materials (expensive), e.g. concrete, to build unnatural looking defences. They usually last longer.

Question 3

Explain what each hard engineering scheme is, how they work and the pros/cons.

Answer 3

Flood Walls:
The construction of a high wall alongside a river to increase its capacity.
Pros:
-A fairly cheap, “one off”, build and cost which will last.
-Useful in cities were space is limited.
Cons:
-Can be expensive, £1.4 million in Cockermouth.
-Disperses flood water, could lead to flooding downstream.

Levees:
Again increasing the capacity of a river by building (normally at a distance) levees.
Pros:
-Allow people to live or farm by a river with a reduced risk of flooding.
Cons:
-Up to £1 million in costs.
-Increases flood risk downstream.
-Can fail as a result of overtopping, slumping or erosion.

Dredging and Flood Relief Channel:
Removing sediment at the base of a river (dredging) or creating extra channels to divert floodwater.
Pros:
-Protects built up areas.
-Cheap to maintain.
Cons:
-Causes flooding downstream.
-Dredging costs around £50,000 annually.
-7KM scheme in Exeter (2015) cost £30 million.
-1KM scheme in Rotherham (2008) cost £14 million.

Question 4

Explain what each soft engineering scheme is, how they work and the pros/cons.

Answer 4

Flood Plain Retention:
Certain grasslands and shrubs are restored so that they can retain water for longer.
Pros:
-Increased ability to hold floodwater.
-Flooding reduced in 2007, Darlington.
-The only flooding in Darlington was a result of backlogged drains.
Cons:
£1.2. million for a 2KM stretch.

River Channel Restoration:
Meanders are rebuilt to slow the river, also hard engineering is replaced with soft engineering.
Pros:
-Improved ecology, increase of 30% in wildlife.
-People like the natural look.
Cons:
-£1.2 million for a 2KM stretch.

Afforestation:
Planting trees in the upper course of the river to intercept rainfall to allow for more evapotranspiration.
Pros:
-Improves the view of an area.
-Low maintenance.
Cons:
-Trees are expensive to purchase and saplings will take years to grow and become effective.