geology ch. 17
secondary porosity
% added openings; develops later; it is the result of fracturing, faulting, or dissolution
Primary porosity
% pore space; the initial void space present (intergranular) when the rock formed
contamination of groundwater
1. Agricultural activities- fertilizers, livestock waste, pesticides 2. municipal activities- salt for streets, tire rubbers, sewer pipes and sewage plants 3. industrial activities- mine drainage, chemical waste and spills 4. individual activities- septic tanks, cleaners, detergents, paints, pesticides
Hydrological cycle
1. Evaporation: solar radiation provides energy 2. transpiration: evaporation from plants 3. precipitation: rain/snow 4. runoff: water flowing over land surface 5. infiltration: water soaking into the ground
geyser cycle
1. groundwater enters chambers and heated by surrounding rock 2. water under great pressure because the weight of overlying water 3. expands and forced out of surface
Effects of Groundwater
Acidic groundwater dissolved limestone along joints and bedding planes
Why does the water table follow the topographY!?!?
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aquifers
a body of saturated rock or sediment through which water can move easily (sandstone, conglomerate, fractured limestone, fractured igneous rocks and metamorphic rocks); transmits ground water freely
Well
a deep hole dug or drilled into the ground to obtain water from an aquifer; bore into the zone of saturations
Spring
a place where water flows naturally from rock or sediment onto the ground surface; they occur where the water table intersects the land surface; they also occur where water flows out from caverns or along fractures and faulrs
Groundwater Recharge
about 15% of the total precipitation infiltrates into the ground and ends up as groundwater
perched water table
above and separated from main water table by an unsaturated zone (commonly produced by thin lenses of impermeable rock (shale clays) within permeable ones)
discharge area
along a stream where groundwater is flowing back to the surface; can also occur at springs, lakes, wetlands, coastal areas, plant transpiration
artesian
any situation in which the groundwater under pressure rises above the level of the aquifer; for an artesian system to exist water has to be confined to an aquifer that is inclined and aquitards both above and below the aquifer must be present to prevent water from escaping (confined aquifer)
confined aquifers
are permeable rock units that are overlain by impermeable rock or clay that limits groundwater movement into, or our of, the confined aquifer; usually deeper underground than unconfined; groundwater in these is usually under pressure and will rise up inside a borehole drilled into the aquifer; they may be replenished or recharged; groundwater in these can sometimes be thousands of years old
unsaturated zone
area above the water table that includes capillary fringe and zone of soil moisture; also called vadose zone; pore spaces contain both air and water
karst topography
area with rolling hills, disappearing streams, and sinkholes; occur in many areas underlain by limestone
sinkholes
caves near the surface that have collapsed; can develop gradually bc soil is dissolved and bedrock surface is lowered; can form abruptly when the roof of a cavern collapses- usually very deep
pore space
depends of size and shape of the grains, degree of sorting
stalagmites
dripstone that forms on the floor and reach upward to the ceiling; formed by water dripping down and building up
stalactites
dripstone that hangs from the ceiling and form where water seeps through cracks
hydraulic conductivity
groundwater flows more rapidly through sediments having greater permeability than through materials having lower permeability
capillary fringe
groundwater held by surface tension in tiny passages
Unconfined aquifers
groundwater in these aquifers are recent and is in direct contact with the atmosphere through the open pore spaces of the overlying soil/rock; usually recharged by rain or stream water infiltrating directly through the overlying soil
soda straw
hollow tube stalactite
geysers
hot springs that periodically erupt hot water and steam minerals often precipitate around geysers as hot water cools rapidly in the air
aquitards
impermeable layers that hinder or prevent water movement; rock/sediment that retards ground water flow due to low porosity and/or permeability (shale, clay, unfractured crystalline rocks)
Groundwater uses
irrigation, public supply, domestic, industrial, livestock, agriculture
Tower Karst
landscape is a maze of isolated steep sided hills; forms in wet tropical and subtropical regions with thick beds of highly jointed limestone
Groundwater
lies beneath the ground surface, filling pores in sediments and sedimentary rocks and fractures in other rock types 1. represents .6% of the hydrosphere 2. recharged by slow infiltration of precipitation 3. generally cleaner than surface water 4. accessed by wells ** represents the largest reservoir of freshwater that is readily available to humans
Groundwater movement
movement of groundwater through pores and fractures is relatively slow compared to flow of water in surface streams; flow velocity depends on slope, permeability
caves
naturally formed underground chambers; an effect of groundwater action; caverns created at or just below water table where acidic groundwater weakens rocks and slow dissolves to create cavities
water table helps..
predict productivity of wells, explain changes in flow of springs/streams, account for fluctuating levels of lakes
flowing artesian well
pressure surface is above the ground and a well is drilled into the aquifer
Geothermal energy
produced using natural steam or superheated water; no carbon dioxide or acid rain produced (only clean energy); some toxic gases given off (sulfur compounds); can be used directly to hear buildings; superheated water can be very corrosive to pipes and equipment
Losing stream (connected)
provide water to the groundwater system b/c of outflow through stream bed; elevation of water table must be lower than surface of the stream
gaining streams
receive water from the groundwater system; elevation of the water table must be higher than the level of the surface of the stream for this to occur
dripstone
speleothems is the collective name for dripstone features found in caverns
Hot springs
springs in which the water in warmer than human body temperature; groundwater heated by nearby magma bodies or circulation to unusually deep/warm levels within the crust; hot water is less dense than cool water and thus rises back to the surface on its own
saturated zone
subsurface zone in which all rock openings are filled with water
permeability
the capacity of a rock to transmit fluid through pores and fractures (the interconnected pores); the smaller the pore spaces the more slowly water moves
zone of soil moisture
the near surface zone that soaks in water and is held by molecular attraction
Porosity
the percentage of voids or pore spaces in the rock or sediment porosity= volume of pore space/ (total volume or rock and/sediment + pore space)
specific retention
the portion of groundwater that is retained as a film on particle and rock surfaces and tiny openings
specific yield
the portion of groundwater that will percolate downward under gravity's influence
nonflowing artesian
the pressure surface is below ground level
vadose zone
unsaturated region above water table
water table
upper limit of zone of saturation; follows topography; water level at surface of most lakes/rivers corresponds to local water table
hydraulic gradient
water table slope; the steeper the slope, the faster the water moves
artesian well
wells in confined aquifers, water may rise naturally to the ground surface because of a confined pressure
non-artesian well
wells in unconfined aquifers, water does not flow naturally to the surface but has to be raised by pumping or other artificial means; water level before pumping is the water table; water enters well from pore spaces within the surrounding aquifer; water table can be lowered by pumping, a process known as drawdown
losing stream (disconnected)
when losing streams are separated from the groundwater system by the unsaturated zone a bulge may form in the water table
recharge areas
where groundwater is being replenished
zone of saturation
zone after zone of soil moisture; all open spaces in sediment and rock are completely filled with water; also called phreatic zone; water in this zone is called GROUNDWATER