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Flashcards in Water below ground Deck (25):

Key features of groundwater

- 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


Recommended using

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


Porosity depends on...

well or poorly sorted granular
- joint & bedding planes fractures in crystalline rock



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


infiltration rate

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


Infiltration capacity

- maximum rate soil can absorb at a steady rate
- varies with soil wetness


Saturated hydraulic conductivity

infiltration through a saturated soils surface


infiltration controls

- 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


Forces acting on water

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



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


Unconfined Aquifer

- has a water table, and is sonly partly filled with water
- rapidly recharged by precipitation infiltrating down to the saturated zone


Confined Aquifer

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


Darcys law

flow occurs due to differences in elevation and pressure


hydraulic conductivity

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


Gaining steams

receive water from the saturated zone
- is a local water table


losing streams

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


intermittent streams

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


Hot water underground

- 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


how water can gain heat

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


Geothermal energy

- 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


Effects of pumping (contamination)

- 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


Balancing withdrawal and recharge

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


Heavy use of groundwater

- 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


Groundwater usage

- 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


Measurement of soil moisture

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