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!?!?

_____

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