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27 Cards in this Set

  • Front
  • Back
Groundwater is important for the following
reasons:
1. Major part of the Hydrologic Cycle.
2. 25% of all freshwater on Earth.
3. Commonly associated with environmental
problems
In regard to the inventory of water on Earth, groundwater is
he largest freshwater reservoir that is readily available. It constitutes upward of 25% of all freshwater.
Aquifer
geological materials such as rocks and sediments that can store and
transmit large quantities of groundwater. Aquifer properties include porosity and
permeability.
Porosity
is the % volume that is empty space. In effect, the amount of open space
in a rock or sediment body that can hold water.
Permeability
is a measure of how “connected” the pore spaces are, therefore
allowing water to flow into and out of the aquifer.
A good aquifer is a body of rock or sediment that has
has both a high porosity
and Permeability
Examples of good aquifers
are sand bodies, sandstone formations, or any highly
fractured rock.
Examples of rocks that do not allow water to flow (Aquaclude)
include shale, rock salt, or any rock body that has secondary cement that has filled
the pores.
Water wells are
holes that are drilled or dug into aquifers to
intersect the water table. Because shale lacks permeability, a well in a shale formation would be a poor water producer.
fracture granite,
wells that intersect fractures will produce water, while adjacent wells that do not intersect fractures will be dry wells.
Groundwater Table.
is the boundary between the
unsaturated (vadose) zone and
saturated zone of an aquifer
vadose zone
is where precipitation soaks into the ground and then migrates slowly to recharge the aquifer.
saturated zone
s the
aquifer. A partially saturated
zone occurs directly above the
GWT and is known as the
capillary fringe.
The groundwater table will
rise and fall with the dry and wet seasons
Aquifer Types
1.Unconfined–shallow aquifers at Earth’s surface, usually made of sand and gravel,no capping impermeable layer.
2. Confined–deep bedrock aquifer (sandstone, limestone) “sandwiched” between two impermable layers (shales).
The recharge area
is the land surface that receive precipitation that eventually soaks into
the ground and fills the aquifer. The deeper the aquifer, the longer the recharge time.
Groundwater
does not flow directly “down hill”, but moves
from regions of higher water pressure to regions of lower water pressure.
Unconfined Aquifer
the groundwater table is
shown to lower from the
wet to dry season, figures A
and B respectively. This is a
natural process that occurs
annually in most places.
Note that during the dry
season, the spring will dry
and the well at the top of
the hill will no longer have
access to groundwater.
Complex Aquifer System
The Floridian Aquifer System is an excellent example of a regional confined aquifer.
Flowing Artesian Wells
f the area of recharge is at a considerably higher elevation than the confined aquifer, then the
groundwater exists under pressure in the area of lower elevation, as shown in the diagram
below. The projection of the groundwater table (red dashed line) from the area of recharge out
over the area of lower elevation shows the elevation that the groundwater would flow to if the
aquifer pressure is released with a well.
Potentiametric Surface,
it’s the potential level that the groundwater will flow up to if released. This type of free flowing well is known as Artesian.
Groundwater flows in the direction
from high to low water pressure.
lakes and streams are places where
the water pressure is equal to the depth of water in the water body, and tends to be low.
groundwater typically flows toward
open water bodies to
merge with the surface water system. So, ultimately the water that enters the ground, will eventually make it back to the surface. This process have given rise to the phrase, “What goes down, must come up.”
The rate of recharge is dependent on
the depth of the aquifer and the nature of confinement, or not. Below there are three aquifers, one is unconfined and the lower two are confined. Although the
aquatards separate the confined aquifers, over time they can still transmit water. So the recharge time of the deeper aquifers is considerably longer than the unconfined aquifer.
Springs
Places where the groundwater table intersects the land surface results in
water resurgence, or springs.
different types of springs
A.Fracture springs.
B. Cave or karst springs.
C. Unconfined aquifer springs.
D. Fault seepage springs.