Tidal Power

Question 1

How are tides produced?

Answer 1

The gravitational attraction between the Earth and the moon creates tidal flow of water that produces 2 periods of high water and 2 periods of low water in each 25 hour cycle

Question 2

Where can tidal power be harnessed?

Answer 2

The speed of water flow in most areas of sea are too slow to harness but the flow may be focused, and velocity increased by coastal features and seabed topography

Question 3

What 3 methods are there for harnessing tidal power?

Answer 3

Tidal barrages
Tidal lagoons
In-stream turbines

Question 4

How do tidal barrages allow tidal power to be harnessed?

Answer 4

It is a dam across an estuary or bay in which turbines are located
This means all water flowing in or out of a lake created behind the barrage flows over the turbines

Question 5

Name an advantage of tidal barrages

Answer 5

It makes maximum use of the tidal flow of water in and out of an estuary or bay

Question 6

Name a disadvantage of tidal barrages

Answer 6

Financial and environmental costs are high

Question 7

How are tidal lagoons different to tidal barrages?

Answer 7

They only surround a selected part of an estuary or bay, dont stretch all across it
This earns only part of the area is effected unlike barrages, and ecologically sensitive areas can be avoided

Question 8

What do some tidal lagoon schemes propose?

Answer 8

Multiple lagoons next to each other e.g. Bristol Channel

Question 9

What can happen if the demand for energy is too low when it is being generated?

Answer 9

Water can be pumped into a lagoon using the surplus energy, producing a higher water level than the sea
Electricity can be generated later when demand is high without the need for tidal water flow

Question 10

How do in-stream turbines work?

Answer 10

They are fixed to the seabed and absorb the kinetic energy of natural tidal flow

Question 11

Compare in-stream turbines to tidal lagoons and tidal barrages

Answer 11

They harness much less energy than a barrage or lagoon
The environmental impacts are very low because they dont have any significant impact on tidal flow

Question 12

What are the advantages of tidal power?

Answer 12

They are predictable: the position of the sun and moon can be predicted meaning the times and ranges of tides can be
A tidal barrage on a large estuary would have a large electricity output compared to most other renewable energy schemes

Question 13

What are the disadvantages of tidal power?

Answer 13

They are intermittent so it makes it difficult to meet continual demand
There are few sites where it would be economically viable
The environmental impacts of barrages are larger than that of other renewable schemes

Question 14

Why is it rare to find locations where tidal power is economically viable to exploit?

Answer 14

Seawater usually moves quite slowly

Question 15

What locational features make tidal power viable?

Answer 15

Coastal feature like estuaries and headlands may concentrate the flow and increase water velocity
If tidal range is large and the mass of moving water is, it might be viable to harness

Question 16

What are 4 named environmental impacts of tidal barrages?

Answer 16

Materials
Tidal range change
Sedimentation
Pollutant concentration

Question 17

What are the environmental impacts of tidal lagoons because of the materials?

Answer 17

• the size of of a large barrage requires large quantities of material for construction, these have environmental impacts during extraction,processing,transport and installation
  E.g. rock,cement

Question 18

Explain tidal range change as an environmental impact of tidal power

Answer 18

The barrage reduces the ease of water flow in and out a lagoon, high tide not as high and low not as low

Question 19

Explain why sedimentation is an environmental impact of tidal power schemes

Answer 19

Because of barrages, there are some areas of fast water flow where sediments can be eroded and carried away, but there is also areas of very slow water, meaning sediments can be deposited and may build up.
Sediments settling will mean the turbidity is lower.

Question 20

Why is pollutant concentration an environmental impact of tidal power schemes?

Answer 20

Pollutants from human activities around lagoons or in catchment areas may build up in lagoons

Question 21

How do the environmental impacts in tidal lagoons compare to those in tidal barrages?

Answer 21

They are similar but on a smaller scale- because they don’t involve a whole estuary
There are more chances to avoid sensitive areas e.g. avoid migratory species paths

Question 22

How do the environmental impacts of in stream turbines compare to lagoons and barrages?

Answer 22

They dont block the natural tidal flow so dont have the same impacts

Question 23

What environmental impacts do in-stream turbines have?

Answer 23

They can produce noise that affects marine animals like whales and dolphins
The effect is localised unless a large amount were installed over a large area

Question 24

Why have new proposed tidal technologies not been tested?

Answer 24

Because tidal power isn’t widely used

Question 25

Explain how one new proposed tidal power technology works

Answer 25

Tidal reefs
Similar to a barrage in that it crosses an estuary but it is not as tall so water can flow over and marine organisms can still move