Groundwater

Question 1

Porosity

Answer 1

The percentage of the total volume that is made up of pore spaces or voids.

Question 2

Porosity depends on

Answer 2

1. Shape and arrangement or particles
2. Grain size distribution
3. Amount of cement present
4. Fracturing which forms joints and fissures

Question 3

Permeability

Answer 3

The capacity of a rock for transmitting water

Question 4

Gravity

Answer 4

The main force causing groundwater to flow. Causes water to percolate downward from surface and spread out.

Question 5

Molecular attraction

Answer 5

The forces of attraction between the walls of a void and the water molecules and mutual attraction between water molecules.
Important in rocks with small voids and depends how much water will be retained.

Question 6

Capillary action

Answer 6

Involves the raising of water in capillary tubes as result of water tension

Question 7

Water table

Answer 7

Areas with adequate rainfall permeable rocks below certain level are saturated with water under hydrostatic pressure. Voids completely filled. This is the saturated zone and the upper surface is the water table.

Question 8

Aerated zone

Answer 8

Permeable rocks lying above the saturated zone, since voids contain air besides water.

Question 9

Springs

Answer 9

A natural outporing of groundwater from the underlying rocks on to the surface due to water table rising

1. Stratum spring
2. Valley spring
3. Fault spring
4. Artesian spring

Question 10

Stratum spring

Answer 10

Arise when downward-percolating water in a permeable formation reaches a impervious layer and spring occurs where the contact crops out

Question 11

Valley spring

Answer 11

Forms where surface level falls below the water table

Question 12

Fault spring

Answer 12

Form when permeable formation is brought against impermeable rocks by faulting

Question 13

Artesian spring

Answer 13

Water emerges under pressure as a consequence of being entrapped in a geological formation so that the water table is at a higher elevation than the exit of spring

Question 14

Doline

Answer 14

A surface depression which forms slowly over a period or years.
Results from lowering of water table. Previously water saturated material such as unconsolidated debris and wad, compact on loss of water leading to relatively low subsidence.

Question 15

Sinkholes

Answer 15

Series of interconnected solution caverns forms immediately below water table. Above water table steeply-inclined joints and fissures are widened by solution and become chocked by soil and relatively insoluble chert. If water table is lowered below the zone of caverning the material chocking the fissure is eroded into the underlying cavern by downward flowing water