Water supply

Question 1

What is porosity

Answer 1

The volume of pore space

Question 2

What is permeability

Answer 2

Rate at which a fluid flows through a rock

Question 3

How do you calculate porosity percentage

Answer 3

Total volume of pore space/total volume of rock or sediment *100

Question 4

How do you calculate premeability

Answer 4

Distance water has traveled/time taken

Question 5

What are the factors affecting porosity

Answer 5

Rock type
The degree of sorting (well sorted rock has high porosity)
The amount of diagenesis (a loose unconsolidated rock has a much higher porosity than a rock that has undergone compaction
Grain shape (rocks containing rounded grains has a higher porosity than angular)
The packing o the grains
GRAIN SIZE IS NOT A FACTOR IN POROSITY

Question 6

What are the factors affecting permeability

Answer 6

Grain size (course grained rocks have a higher permeability than fine grained rocks because there is less resistance to flow around coarse grains)
High porosity

Question 7

What is the water table

Answer 7

The level at which water sits within the ground

Question 8

What is the height of the overlying column of water known as

Answer 8

The hydro static head

Question 9

How do you calculate the hydraulic gradient

Answer 9

difference in hydro static pressure or head/distance between two points

Question 10

What is an aquifer

Answer 10

A body of porous and permeable rock capable of storing and yielding significant amounts of water

Question 11

What is a recharge zone

Answer 11

Area of an aquifer open to the atmosphere, allowing replenishment of water

Question 12

What is an aquiclude

Answer 12

An impermeable rock that does not transmit water

Question 13

What are the two main types of aquifers

Answer 13

Unconfined aquifer-open to the atmosphere, under atmospheric pressure and is recharged by rainwater from directly above. Water will need to be pumped to the surface from a well or borehole sunk into an unconfined aquifer
Confined aquifer is overlain by impermeable rocks and the groundwater held within it is under hydro static pressure. Groundwater can only be replenished in a confined aquifer if it has recharge zones that are open to the atmosphere

Question 14

What is a live or fossil aquifer

Answer 14

Live-one that is currently being replenished by rainwater via a recharge zone on the surface
Fossil-One that is no longer being replenished and represents a relic of a past wetter climate

Question 15

What is an artesian basin

Answer 15

A large, synclinal confined aquifer under hydrostatic pressure

Question 16

What is an artesian well

Answer 16

Hold water under hydrostatic pressure, which rises up the well on release

Question 17

How is ground water abstracted

Answer 17

By sinking a borehole and pumping the water to the surface, as water is pumped up the level of the water table falls, leading to a cone of depression

Question 18

What is the cone of depression

Answer 18

Occurs where there is a lowering of the water table in the vicinity of a well

Question 19

What is the draw down

Answer 19

Describes the height difference between water table and water level in the well

Question 20

What are the main problems caused by groundwater extraction

Answer 20

Lowering of the water table
Subsidence at the surface resulting from the removal of water from the pore spaces of rocks
Salt water encroachment in coastal areas

Question 21

What are the threats to ground water supply

Answer 21

Over-pumping

Pollution- groundwater is vulnerable to contamination, once polluted it is difficult to clean

Question 22

What are the sources of groundwater pollution

Answer 22

Nitrates, pesticides and microbes from run-off
hydrocarbon and solvents from petrol stations and factories
Toxic fluids from landfill waste disposal sites
Acid mine drainage water containing toxic metals such as lead and cadmium from coal and metal mines

Question 23

What are springs

Answer 23

Occur when the water table meets intersects the land surface and groundwater flows out onto the surface

Question 24

What are the types of springs

Answer 24

Lithological springs-result in change of rock type, occur where porous and permeable rock overlies impermeable rock, the water table will intersect the land surface at the junction between the two rock types, there will be a spring line along the base of the permeable rock
Springs at faults-If faults have moved porous and permeable rock into contact with an impermeable rock a spring line will occur where the fault plane intersects the land surface
Springs at unconformities-If porous and permeable rock lies uncomfortably on top of impermeable older rock the water table will intersect the land surface at the junction between the two rock types, a spring line will occur where the line of the unconformity intersects the land surface

Question 25

Advantages and Disadvantages of surface water supply

Answer 25

Advantages
Easy to abstract
Hydroelectric power generation
Reservoirs can be used for recreation and other purposes

Disadvantages
Water will need treatment
Water levels vary between seasons
Requires construction of environmental damaging dams
Reservoirs eventually silt up

Question 26

Advantages and Disadvantages of ground water

Answer 26

Advantages
Rocks at as a natural filter
No evaporation
Pumping cost is usually low

Disadvantages
Requires sedimentary rocks and presence of aquifers 
Surface subsidence
Pollutants have a long residency time
Water might be brackish