River management

Question 1

Dams and resevoirs

Answer 1

Dams are barriers built across the rivers, usually in the upper course
A reservoir (artificial lake) is formed behind the dam

+ Reservoirs store water (e.g after heavy rain), control water flow and prevent floods downstream.
They also can be used to generate hydroelectric power

• Dams are very expensive to build. Creating a reservoir canflood existing settlements.
  Material is deposited in the reservoir not along river course, so farmland downstream can become less fertile

Question 2

Channel straightening

Answer 2

Meanders are removed by buildings straighter artificial channels

+ Water leaves the area more quickly rather than building up,so flood risk is lower

• Flooding may happen downstrean instead.
  Faster moving water may cause more erosion downstream.

Question 3

Embankments

Answer 3

Raised walls are built along river banks

+ The rivers can hold more water, so floods are less frequent

• They’re quite expensive, and there’s a risk of severe flooding if the water rises above the level of the embankments or if they break

Question 4

Flood relief channel

Answer 4

Channels are built to divert water around built-up areas or to divert excess water if the river level gets too high

+ Gates on the channels means the release of water can be controlled reducing flooding risk

• There will be increased discharge where the relief channel rejoins the river (or joins another river), which could cause flooding in that area

Question 5

Flood warnings and prepartion

Answer 5

The environmental agency issues flood warnings through various media (e.g. TV, radio, internet) Buildings are modified to minimise flood damge.
Residents can prepare sandbags and flood boards prior to floods

+ Warnings give people time to move possestions upstairs, put sandbags in place or evacuate. This reduces the impact of flooding

• Warning don’t prevent floods. People may not have access to warnings and modifying buildings is expensive. Preperation doesn’t guarntee safety from flood and give people a false sense of security

Question 6

Flood plain zoning

Answer 6

Restrictions prevent buildings on parts of a flood plain that are likely to be affected by a flood

+ Flood risk is reduced-fewer impermeable surfaces are created (e.g roads). The impact of flooding is also reduced - there are no buildings to damage

• The expansion of an urban area is limited if there aren’t any other suitable building sites. It can’t help in areas with existing buildings

Question 7

Planting trees

Answer 7

Planting trees in the river valley increases the interception of rainwater (and lag time).

+ Discharge and flood risk decrease. Vegetaion reduces soil erosion in the valley and provides habitats for wild life

• Less land is avaliable for farming

Question 8

River restoration

Answer 8

Making the river more natural e.g. by removing man-made levees, so that the flood plain can flood naturally.

+ Discharge is reduced, so there’s less risk of flooding downstream. Little maintanence is neededandthere are better habitats for wildlife

• Local flood risk can increase, especially if nothing is done to prevent major flooding