Groundwater

Question 1

what is ground water

Answer 1

water that infiltrates into the ground

Question 2

how is water available to us?

Answer 2

Most fresh water on Earth tied up in glacial water

Most fresh water comes from groundwater aquifers
- Underground layers of permeable soil, sediment or rock that host extractable groundwater

Most fresh water used for irrigation (in agriculture), less for residential use

Question 3

what is the zone of aeration

Answer 3

pores contain water + air

Question 4

what is the of saturation

Answer 4

pores contain water only

Question 5

where is the water table located?

Answer 5

top of zone of saturation

Question 6

where does groundwater occur?

Answer 6

in the zone of saturation (below water table)

Question 7

storage capacity of an aquifer is controlled by what?

Answer 7

by porosity (spaces in material)

Question 8

what is the ability to flow

Answer 8

permeability (interconnectedness of pores)

Question 9

what is a runoff of water

Answer 9

runoff occurs when there is more water than land can absorb

Question 10

What is the groundwater relationship with surface water

Answer 10

Addition to water from runoff, streams can also receive water from groundwater sources

This is why river level can remain high long after an event of heavy rainfall (takes time for groundwater to reach the river)

Question 11

what is the flow behaviour of groundwater

Answer 11

Water flows very slowly downslope in generally predictable pattern (provided that the characteristics of the material is fairly uniform)

Water table contours represent line of equal elevation above sea level

Question 12

what are the two main types of aquifers

Answer 12

Unconfined aquifer
Confined aquifer

Question 13

what is a unconfined aquifer?

Answer 13

an aquifer that receives water directly from the land surface above

Question 14

what is a confined aquifer

Answer 14

an aquifer that is overlain by a layer of relatively impermeable material (commonly clay or clay-rich rock) that limits groundwater movement in or out the aquifer

Question 15

what is an aquitard

Answer 15

An impermeable unit of material

Question 16

what are the important feature of aquifer

Answer 16

Flow direction

Recharge area

Aquifers (confined, unconfined)

Aquitards

Perched water table

Additional features:

Influent stream (loses water to groundwater system)

Effluent stream (gains water from groundwater system)

The buildup of water over a local aquitard produces a spring

Question 17

What type of system “pumps themselves” and why?

Answer 17

Artesian Systems

Artesian systems “pump” themselves” due to water table in recharge area being at a higher elevation than land surface above a well in confined aquifer in a lower-lying area (creates “hydraulic head”)

Question 18

what is a artesian system

Answer 18

The higher the water level, the higher the water pressure

The downward “push” of the water (hydraulic head) helps the delivery of water through pipes to homes

Question 19

What are the groundwater consequences when water exceeds recharge

Answer 19

Local drawdown of water table

Formation of cone of depression

Cone of depression expands laterally as more water is withdrawn

Question 20

what is consequences of water overdraft

Answer 20

Agricultural demand (irrigation)

Output&raquo_space; input

Regional drawdown of water table

Shrinking water supplies

Consequences:

Compaction

Permanent lowering of permeability

Subsidence (sinking of land)

Question 21

What are the consequences of withdrawal of groundwater

Answer 21

Increased flood hazards, more runoff due to decreased permeability, greater concentration of pollutants in wetlands

In coastal areas, excessive groundwater withdrawal (from freshwater lens) can lead to an inflow of salt water (from the sea)

Question 22

what is a septic tank sewage disposal

Answer 22

Contaminated water slowly infiltrates into soil, organic contaminants naturally broken down by bacteria in soil

Under normal conditions, “beneficial” bacteria naturally occurring in the soil dominate over potentially harmful bacterial strains

Question 23

what are the effects on permeability on groundwater flow?

Answer 23

Contaminated water may be “purified” by beneficial microbes as the groundwater is flowing relatively slowly through moderately permeable sandstone

Highly permeable limestone (w/ large holes dissolved in the rock) allows groundwater to move too quickly to allow beneficial microbes to “purify” the water of contaminants

Question 24

How do we avoid polluting drinking water sources?

Answer 24

We can predict effects of water table drawdown + the migration of the septic plume
- Excessive pumping can alter direction of groundwater flow

Groundwater moves through high permeability materials faster than less permeable materials
- Less time for microbes to filter out contaminants

Question 25

what is Karst

Answer 25

Dissolution of carbonate sedimentary rocks by groundwater produces a distinctive type of land topography called karst

Characterized by underground drainage systems (dissolved by groundwater) with caves/caverns + sinkholes (produced when caves collapse)

Question 26

when do sinkholes form

Answer 26

Form when the “roofs” of caves collapse

Collapse events often spectacular

Common in temperate to tropical regions underlain by carbonate rocks