4.8 Flood Risk And Management Flashcards
Why is river flood risk increasing? Include global climate change and
human activity in drainage basins
Concrete surfaces are almost completely impenetrable to water. Rainwater gushes off these surfaces and overwhelms our drains.
Over 82% of people in the UK live in towns and cities, and this number is steadily increasing. That means more concrete being poured over the land every year, increasing the risk of floods.
When seawater is drawn inland during a storm surge, or coastal rivers overflow due to heavy rain, low-lying marshes nearby act as a temporary basin that absorbs the excess water.
Over hundreds of years, many large areas of marshland, such as The Fens in eastern England, have been cleared for agricultural use.
Draining marshes means those areas will stay dry for all but the biggest floods. But the excess water can overrun into surrounding areas – increasing the risk
Since Neolithic times, people have been clearing woodland to make space for housing and farming. Today more than 70% of UK land is agricultural plots – much of this cleared from ancient forests.
Woodland soil is very absorbent. Tree roots and decaying plant material help loosen the soil, which lets rainwater flow down towards the bedrock. Converting this into the compacted soil of farmland has reduced the ground’s ability to hold excess rainwater, increasing surface run-off.
Woodland cover in the UK reached its lowest point during WW1, at around 5%. The Forestry Commission was established in 1919 to turn this around, and now woodland cover is just under 12%. But the UK is still one of the least wooded countries in Europe.
Since Neolithic times, people have been clearing woodland to make space for housing and farming. Today more than 70% of UK land is agricultural plots – much of this cleared from ancient forests.
Woodland soil is very absorbent. Tree roots and decaying plant material help loosen the soil, which lets rainwater flow down towards the bedrock. Converting this into the compacted soil of farmland has reduced the ground’s ability to hold excess rainwater, increasing surface run-off.
Woodland cover in the UK reached its lowest point during WW1, at around 5%. The Forestry Commission was established in 1919 to turn this around, and now woodland cover is just under 12%. But the UK is still one of the least wooded countries in Europe.
Compare how soft and hard engineering schemes work
Soft engineering options are often less expensive than hard engineering options. They are usually more long-term and sustainable, with less impact on the environment. There are two main types of soft engineering. This replaces beach or cliff material that has been removed by erosion or longshore drift.
Hard engineering - this involves building structures to protect the coast. Soft engineering - this involves working with nature by using natural materials or allowing nature to take back areas.
Explain what each hard engineering scheme is, how they work and the
pros/cons
Building a sea wall
A wall built on the edge of the coastline.
Advantages
Protects the base of cliffs, land and buildings against erosion. Can prevent coastal flooding in some areas.
Disadvantages
Expensive to build. Curved sea walls reflect the energy of the waves back to the sea. This means that the waves remain powerful. Over time the wall may begin to erode. The cost of maintenance is high.
Building groynes
A wooden barrier built at right angles to the beach.
Advantages
Prevents the movement of beach material along the coast by longshore drift.
Allows the build up of a beach. Beaches are a natural defence against erosion and an attraction for tourists.
Disadvantages
Can be seen as unattractive.
Costly to build and maintain.
Rock armour or boulder barriers
Large boulders are piled up on the beach.
Advantages
Absorb the energy of waves.
Allows the build up of a beach.
Disadvantages
Can be expensive to obtain and transport the boulders.
Explain what each soft engineering scheme is, how they work and the
pros/cons
Beach nourishment
This replaces beach or cliff material that has been removed by erosion or longshore drift.
The main advantage is that beaches are a natural defence against erosion and coastal flooding. Beaches also attract tourists.
It is a relatively inexpensive option but requires constant maintenance to replace the beach material as it is washed away.
Managed retreat
Areas of the coast are allowed to erode and flood naturally. Usually this will be areas considered to be of low value - eg places not being used for housing or farmland.
The advantages are that it encourages the development of beaches (a natural defence) and salt marshes (important for the environment) and cost is low.
Managed retreat is a cheap option, but people will need to be compensated for loss of buildings and farmland.
