Hard Engineering Flood Management

Question 1

Define Hard Engineering.

What are the general disadvantages of it?

Answer 1

Hard engineering defences are man-made structures that reduce flooding.

The general disadvantages of hard engineering defences include:

• They’re expensive to build and maintain, and need technical skill. Poorer countries, i.e. LEDCs, often can’t afford these flood defences.
• Floods happen less often, but they can be more hazardous if they do happen. E.g. if a dam breaks then a huge amount of water will rapidly flood the land.
• Natural processes are disrupted, e.g. crops don’t get fertile silt from river sediment during low-level flooding.
• Some people think they’re ugly.

Question 2

Explain Dams.

Answer 2

Dams

How it works:

​Dams are huge walls built across rivers. A reservoir (aritifical lake) is formed behind the dam. Flood water is caught by the dam, which prevents flooding downstream. The water is released as a steady flow throughout the year.

Extra benefits:

• Turbines are often built into the dams, which generate HEP (Hydroelectric power) to create electricity.
• Steady water released allows irrigation of land below the dam throughout the year.
• People can utilise the reservoir for recreational activities e.g. sailing.
• The dam provides water supply.

Disadvantages:

• They’re very expensive.
• Land is flooded when a reservoir is created. This often destroys farmland and forces people to move elsewhere - displacement of people.
• They affect wildlife e.g. they can prevent salmon from migrating upstream to breeding grounds.
• They trap sediment normally carried in rivers. This can cause the dam to fail. It can also cause increased erosion downstream, as there’s less protective sediment being deposited.

Question 3

Explain Channel Straightening.

Answer 3

Channel straightening

How it works:

Channel straightening is where meanders are removed by building artifical cut-throughs. This makes the water flow faster, which reduces flooding because water drains downstream more quickly and doesn’t build up to a point where the river can’t contain it any more.

Extra benefit:

It takes less time to navigate the river because it has been made shorter.

Disadvantages:

• Flooding may happen downstream instead, as flood water is carried there faster.
• More erosion occurs downstream because the river flows faster.
• Altering river channels disturbs wildlife habitats.

Question 4

Explain Levees.

Answer 4

Levees

How it works:

Levees are embankments (e.g. mounds of earth and rubble) built along either side of the river. This increases the capacity of the river channel so that the river can hold more water without overflowing, and so it floods less often.

Extra benefit:

They allow the floodplain to be built upon.

Disadvantages:

• They’re quite expensive.
• There’s a risk of severe flooding if the levees are breached e.g. Hurrican Katrina, New Orleans, USA.

Example - the Mississippi river in the USA is heavily Leveed.

Question 5

Explain Diversion Spillways.

Answer 5

Diversion spillways

How it works:

Diversion spillways are 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. They prevent flooding because river discharge is reduced. The spillways often have gates that can be opened, so the release of water can be controlled.

Disadvantages:

• An increase in discharge when the diverted water joins another river (or rejoins the same river) could cause flooding below that point.
• If spillways are overwhelmed, water will flood areas not used to flooding, which could cause even bigger problems.