7 - Surface Hydrology 2

Question 1

Groundwater

Answer 1

All the water that exists in the underground saturated zone
- Water that seeps through soil and does not runoff - stays in ground
30% of freshwater on Earth

Question 2

Methods groundwater leaves the saturated zone?

Answer 2

Springs (15-20%), river and lake seepage (50-60%), evaporation (10-15%) and submarine groundwater discharge (5-10%)

Question 3

Submarine groundwater discharge

Answer 3

the natural flow of groundwater from land to ocean or coastal waters through the seabed.

Question 4

Water table

Answer 4

upper level of an underground surface in which the soil or rocks are permanently saturated with water

Question 5

What makes the water table move?

Answer 5

Changing precipitation, seasonal variation (lowest in summer), plant uptake and water removal, pumping or human changes

Question 6

Aquifers

Answer 6

underground layer of water-bearing material consisting of permeable or fractured rock or of unconsolidated materials

Question 7

Hydraulic head

Answer 7

amount of mechanical energy available in water

Question 8

How is the hydraulic head determined?

Answer 8

By pressure (weight of overlying water) and elevation (distance from the sea). Flows from areas of high (A) to low (B) head

Question 9

Hydraulic gradient

Answer 9

movement from one head to another. Tells us the rate and direction of groundwater flow

Question 10

Darcy’s law

Answer 10

used to calculate speed of groundwater

Question 11

Hydraulic conductivity

Answer 11

how easily does water move through different substances
Aquitards have low hydraulic conductivity (confining layers) e.g. clay, silt

Question 12

Hydraulic conductivity is dependent on?

Answer 12

Porosity, permeability, grain size and sorting, material type, degree of saturation and fluid viscosity and temperature

Question 13

Cone of depression

Answer 13

pumping causes the water table to lower at the well location. For this reason pumps cannot be located too close

Question 14

Impacts of groundwater pumping?

Answer 14

Subsidence, saltwater intrusion, depleted groundwater, streamflow depletion and dry wells

Question 15

Subsidence

Answer 15

process by which an area of land sinks to a lower level than the surrounding land
Causes:
- Groundwater extraction
- Mining
- Oil and gas extraction
- Soil compaction

Question 16

Why is subsidence worst in cities?

Answer 16

Urban deltas sink as ground is soft and cities are heavy, and also due to extracting groundwater (high demand)

Question 17

What is a method to reduce subsidence?

Answer 17

Groundwater injection. This is when surface water (often treated or surplus) is injected into underground aquifers to recharge and restore groundwater levels
E.g. Bangkok - subsidence of 9-10cm became 1-2cm per year

Question 18

Why would groundwater injection not be suitable?

Answer 18

Poor hydraulic conductivity of the soil, risk of contamination, pressure differences can be dangerous