Water

Question 1

What is groundwater?

Answer 1

Subsurface water contained within the porespaces of rocks below the water table.

Question 2

What is the water table?

Answer 2

The level that the water sits within the ground. It is the surface seperating unsaturated rock above from saturated rock below.

Question 3

What is porosity?

Answer 3

The amount of pore spaces in a rock or sediment, usually expressed as a percentage of the total rock volume.

Question 4

What factors affect porosity?

Answer 4

Rock type, degree of diagenesis, degree of sorting, grain shape.

Question 5

What is permeability?

Answer 5

The ability for fluids to flow through a rock. The pore spaces present in a rock may become interconnected and link up to form a pathway.

Question 6

What factors affect permeability?

Answer 6

Grain size, rock type and degree of diagenesis

Question 7

What is hydrostatic pressure?

Answer 7

This results from the weight of the overlying water column and increases with depth.

Question 8

What is hydrostatic head?

Answer 8

The height of the overlying column if water.

Question 9

What is hydraulic gradient?

Answer 9

The difference in hydrostatic pressure between two points divided by the horizontal distance between them.

Question 10

What is an aquifer?

Answer 10

A body of porous and permeable rock capable of storing and yielding large quantities of water.

Question 11

What is an aquiclude?

Answer 11

An impermeable rock that doesn’t transmit water.

Question 12

What types of aquifer are there?

Answer 12

Unconfined, confined, perched, live and fossil.

Question 13

What is a recharge zone?

Answer 13

The area of an aquifer open to the atmosphere allowing replenishment of the water.

Question 14

What is an artesian basin?

Answer 14

A large synclinal confined aquifers.

Question 15

What is a cone of depression?

Answer 15

It is created as groundwater is pumped out from a well and the level of the water table falls around it.

Question 16

What is draw down?

Answer 16

The height difference between the water and the level of water in the well.

Question 17

What affects the cone of depression?

Answer 17

Rate of abstraction, duration of abstraction and hydraulic properties of the aquifer

Question 18

What problems are associated with water abstraction?

Answer 18

Lowering of the water table, subsidence of the ground at the surface and saltwater encroachment

Question 19

What threats are there to groundwater?

Answer 19

Overpumping and pollution

Question 20

What is a spring?

Answer 20

When subsurface water flows onto the surface because the water table intersects the land surface and is a junction between permeable and impermeable rock.

Question 21

How does lithology create a spring?

Answer 21

They occur where porous and permeable rock overlies an impermeable rock. They also occur where impermeable igneous intrusions cut through porous and permeable rocks.

Question 22

How do faults create a spring?

Answer 22

Faults can produce springs if they have moved porous and permeable rock into contact with impermeable rock.

Question 23

How do unconformities create a spring?

Answer 23

If porous and permeable rocks lies unconformably on top of impermeable older rock, the water table will intersect the land surface at the junction between the two rock types

Question 24

What are the advantages of ground water supply?

Answer 24

Rocks act as a natural filter
No loss of water through evaporation
No need for expensive and damaging dams
Pumping costs for an artesian basin will be low

Question 25

What are the disadvantages of ground water supply?

Answer 25

Surface subsidence
Pollutants have a long residence time
Pumping is costly
Not all areas have the required geology
Groundwater is not suitable in coastal areas is not suitable for drinking

Question 26

What are the advantages of surface water supply?

Answer 26

Easy to abstract
Water can be treated after use
Dams can be used for hydroelectric power
Reservoirs can be used for recreation

Question 27

What are the disadvantages of surface water supply?

Answer 27

Water will need treatment
Seasonal as volume of water varies
Requires sufficient rainfall and large catchment areas
Requires construction of dams
Requires flooding of land
Reservoirs will slit up

Question 28

What makes an aquifer renewable?

Answer 28

Live aquifers are a renewable resource as long as the rate of replenishment is greater than the rate of use.