CHPTR 16 Groundwater Flashcards
what percentage of water is groundwater
1%
what percentage of fresh water (excluding ice) is groundwater
90%
phreatic zone
saturated zone; water in this zone is called ground water
soil moisture
some groundwater stays near the surface in the soil
water table
top of the saturated (phreatic) zone
vadose zone
zone of aeration
capillary fringe
random water in the ground outside of the phreatic zone
how can we see the water table
- tops of rivers
- bottoms of wells
porosity
fraction of rock volume that is voids (water or air + joints, faults, caves)
primary porosity
is in structures present when rock forms
secondary porosity
develops in structures after the rock has formed
permeability
measure of how easily fluid can flow through a rock
Specific yield
fraction of groundwater that will drain under influence of gravity
specific retention
fraction of groundwater that will remain under influence of gravity
Porosity equation
Porosity% = Specific Yield% + Specific Retention%
Aquitard
impermeable layer that hinders or prevents groundwater flow
Aquifer
permeable layer that holds enough groundwater to be a useful source
Porosity and permeability of crystalline igneous rock
low porosity
low permeability
Porosity and permeability of shale (clay layers)
hi porosity
low permeability
porosity and permeability of quartz sandstone
hi porosity
hi permeability
porosity and permeability of glacial till
low porosity
low permeability
Darcy’s Law + give it
equation for the calculation of groundwater velocity
V= (kh / pL)
k = constant
h = height
L = horizontal distance
p = porosity
how can we increase the velocity of groundwater
- increase height
how can we decrease he velocity of groundwater
- increase porosity
- increase horizontal distance
perched water table
when an aquitard is situated above the main water table; producing a localized zone of saturation
geyser
produce regular “eruptions” of hot water
cone of depression
area of drawdown that forms around a well. occurs because groundwater flows relatively in response to extraction from aquifer. eventually the flow will level the water table
drawdown
lowering of water table due to withdrawl of water
confined aquifer
an inclined aquifer is surrounded by impermeable beds
unconfined aquifer
overlain by permeable rocks and soil. pressure increased by elevation changes
artesian well
water is in a confined aquifer and rises to a level above the aquifer due to pressure from changing elevations
subsidence
the grounds sinks because of how much and how quickly groundwater is being removed
saltwater intrusion
a natural barrier between salt and freshwater due to the density of seawater being higher than freshwater
brackish water
mixture of seawater and freshwater
acceptable tds in drinking water
500 mg / l
hard water
substantial amounts of dissolved calcium and magnesium
where do most caves form
at or just below the water table in the zone of saturation due to erosion
speleothems
features formed by deposition of chemical sediment
ie. stalactites and stalagmites
stalactite
hangs from the cieling
stalagmite
upward growing mound
Karst topography
groundwater erosion forms distinct features on the surface of the Earth:
- sinks and sinkholes form
- lack of surface streams
most useful paramaters to finding water
electrical resistivity
