U2 T7

Question 1

What is an aquifer?

Answer 1

It’s a layer of rock that holds water.

Question 2

What are the main features of an aquifer?

Answer 2

The main features of an aquifer are:

1. Porosity
2. Permeability
3. Suitable geological structures

Question 3

What is permeability?

Answer 3

It is the measure of ease with which fluids may flow through a rock because of the interconnections between the spaces.

Question 4

What is porosity?

Answer 4

Porosity is a measure of the proportion of the rock’s volume that is space and could therefore hold water.

Question 5

Name 3 different porous rocks that often form an aquifer

Answer 5

1. Chalk (craie)
2. Limestone (calcaire)
3. Sandstone (grès)

Question 6

Name an impermeable rock and say why it is impermeable.

Answer 6

Clay
Have high porosity but the pores are too small for water to flow through easily
Granite is also impermeable

Question 7

How should be the rock below the water bearing. Why? Name 2 rocks that are suitable for that

Answer 7

The rock below the water- bearing rock must be impermeable to prevent the escape of water. Granite and clay are suitable for imperméable materials.

Question 8

How should be some of the rock above an aquifer. Why?

Answer 8

Some of the rock above must be permeable to allow recharge of the aquifer with water from above. Some aquifer are very large and the recharge area may be a long way from the area of abstraction.

Question 9

How may water be abstracted from an aquifer? (3 ways)

Answer 9

The water may be abstracted using a well, a borehole or it may come to surface naturally in springs.

Question 10

What are the consequences of aquifer overuse?

Answer 10

1. Reduced supplies due to extracting water at a faster rate than it is replenished
2. Subsidence as a result of the aquifer drying out and compacting
3. Lowering of the water table lowers and plants can no longer reach it.
4. Salt water incursion if the water table is lowered below sea level.

Question 11

What happens if an aquifer has salt water incursion?

Answer 11

The salt makes the aquifer water unsuitable for irrigation as it could kill the crops by osmotic dehydration.

Question 12

What does osmotic dehydration mean?

Answer 12

It’s the loss of water, especially from crop roots, caused by the low water potential of s’ils with a high salt content.

Question 13

Name a problem for plants if the water table is lowered

Answer 13

Plants with high water requirement will die or become less abundant as they fail to compete with plants that have lower requirement for water.

Question 14

What may happen to wetlands if the water table of underground water is lowered?

Answer 14

Flow from the springs will decline. Because the flow of water into wetland have decline, they may dry up.

Question 15

Where is desalination of seawater used and why?

Answer 15

Desalination of seawater is very energy intensive and expensive ans is only used in countries where seawater is available but there are inadequate supplies of freshwater

Question 16

Why it is often preferable to take water from an aquifer rather than a river?

Answer 16

It can be easier to abstract from a river as it requires less infrastructure. However there is less chance of contamination as it has been naturally filtered as it moves through the rock. This makes it easier and cheaper to treat before sending to the public supply system

Question 17

Is most of the public water supply taken from surface water or groundwater?

Answer 17

Most of public water supply is taken from surface water - about 70%

Question 18

Why might a dependency on seawater as a source of drinking water contribute to climate change?

Answer 18

Desalination requires huge amount of energy. This is likely to come from fossil fuels (solar energy is used in some places but it requires huge array of solar panels). Burning fossil fuels releases CO2 into the air and this is a greenhouse gas and contributes to an increase in global temperatures