Water below ground

Question 1

Key features of groundwater

Answer 1

• largest accessible store of freshwater
• crucial regulator of hydrological cycle through buffering action
• provides 24% of global water supply
• around 50% within 800m of surface
• only source of fresh water in some locations
• often cheapest, quality and relatively low engineering costs
• needs carful management
• 30% of UK’s water supple

Question 2

Recommended using

Answer 2

Subsurface: water for totality of water below ground (unsaturated)
Groundwater: for water in the saturated zone (saturated)

Question 3

Porosity depends on…

Answer 3

well or poorly sorted granular

- joint & bedding planes fractures in crystalline rock

Question 4

infiltration

Answer 4

the process whereby water enters a permeable surface (the soil) before moving downwards by percolation

Question 5

infiltration rate

Answer 5

• volume per time
• changes with soil wetness
• supply limited or soil controlled

Question 6

Infiltration capacity

Answer 6

• maximum rate soil can absorb at a steady rate

- varies with soil wetness

Question 7

Saturated hydraulic conductivity

Answer 7

infiltration through a saturated soils surface

Question 8

infiltration controls

Answer 8

• flow supply
• surface controls (land cover, Topography and morphology, compaction and splash-pans)
• subsurface controls (soil texture, structure, hydrodynamic characteristics, initial soil wetness, hard pans and discontinuities

Question 9

Forces acting on water

Answer 9

• their strength is called soil suction or soil moisture tension
• capillary forces: surface tension and absorption

Question 10

Aquifer

Answer 10

layer of consolidated rock or unconsolidated deposits that is able to transmit and store enough water for extraction

Question 11

Unconfined Aquifer

Answer 11

• has a water table, and is sonly partly filled with water

- rapidly recharged by precipitation infiltrating down to the saturated zone

Question 12

Confined Aquifer

Answer 12

• completely filled with water under pressure
• separated from surface by impermeable confining layer/aquitard
• very slowly recharged

Question 13

Darcys law

Answer 13

flow occurs due to differences in elevation and pressure

Question 14

hydraulic conductivity

Answer 14

The ability of a porous medium to transmit water

• unlike porosity, permeability does depend on grain size
• texture and structure also important
• equivalent to permeability in case of uniform rock
• varies spatially

Question 15

Gaining steams

Answer 15

receive water from the saturated zone

- is a local water table

Question 16

losing streams

Answer 16

Lose water to the saturated zone

• stream beds lie above water table
• maximum infiltration occurs through stream bed, producing permanent mound in the water table beneath dry channel

Question 17

intermittent streams

Answer 17

rivers dry up naturally because the flow lines seasonally drop below the bed level

Question 18

Hot water underground

Answer 18

• hot springs: springs in which the water is warmer than human body temperature
• Geyser: a type of hot spring that periodically erupts hot water a steam; the water is generally near boiling

Question 19

how water can gain heat

Answer 19

• ground water may circulate near a magma chamber or a body of cooling igneous rock
• ground water may circulate unusually deep in the earth

Question 20

Geothermal energy

Answer 20

• Electricity can be generated by harnessing naturally occurring steam and hot water in areas that are exceptionally hot underground
• nonelectric uses of geothermal energy include space heating, paper manufacturing, ore processing and food preparation

Question 21

Effects of pumping (contamination)

Answer 21

• accelerates ground water flow toward well
• captures contamination within cone of depression
• may reverse ground water flow
• can draw contamination up hill
• will cause saltwater intrusion

Question 22

Balancing withdrawal and recharge

Answer 22

to avoid problem of falling water tables, subsidence and compaction, many places use artificial recharge; natural floodwaters or treated industrial or domestic waste-waters are stored in infiltration ponds in the surface to increase the rate of water percolation into the ground

Question 23

Heavy use of groundwater

Answer 23

• a regional water table dropping
• deepening of well means more electricity is needed to pump the water to the surface
• ground surface settling because the water no longer supports the rock and sediment

Question 24

Groundwater usage

Answer 24

• a local supply of groundwater will last indefinitely if it is withdrawn for us eat a rate equal to or less than the rate of recharge

Question 25

Measurement of soil moisture

Answer 25

• Gravimetric method (oven dry and measure weight loss)
• Tensiometer (soil suction pressure measured)
• Capacitance probe (electro-magnetic pulses emitted)