Of The Most Important Source Of Drinking Water Is Lying Beneath The Surface Of
The Earth And Is Called GROUNDWATER
OF GROUNDWATER IS RAIN AND SNOW.
15% of all the precipitation ends up as groundwater.
whole graundwater would make a 10m deep lake which would cover the earth’s
It is the percentage of rock’s volume that can hold
water. Almost every kind of rock can hold some water.
It is depend on size, shape and arrangement of the particles in the rock.
Most igneous and metamorphic rocks have small primary porosity however it can be increased by fracturing, or weathering., or solution.
are rocks such as conglomerate, sandstone, limestone which tend to have large
porosity and can hold a considerable amount of water. Originally loose sediment
have much higher porosity which can be loosen by compaction and so on.
capacity of the material for transmitting fluid is called its PERMEABILITY.
depend on not only on porosity, but also on the size and interconnection of the
pores in the rock.
probably has more pore space than sandstone, however the permeability is small
because the pores are too small and there is no interconnection between them. On
the other hand if the pores are too small there is a molecular interaction
between the mineral and water, so the water becomes unremovable.
areas such as Georgia depend on fractured reservoirs for their drinking water.
velocity: 1m/day!!!!! to 1m/year (the highest ever measured in US. is 250m/day
layer transporting water : AQUIFER
and well rounded gravel
layer preventing water transport called:
Transition between aquifer and aquiclude
water from rain moves subsurface and adheres downward:This zone is called:
here is called: SUSPENDED WATER
spaces in this zone are filled by both air and water
the zone just above the base of zone of aeration. Water in this zone moves
upward because of the surface tension. This phenomena can be seen with larger,
and small tubes put into the water.
water table (above the main wt)
the shape of the water table is a replica of the surface. Therefore it is higher
underneath mountain, or hills, and lower beneath valleys. The unequality of
water table also caused by different rainfall pattern, different permeability.
During dry season it drops, so probably shallow wells would dry out.
enter to the system
leave the system
water moves very slowly by gravitation higher elevation areas toward lower
the water can move upward, against gravity, because of the pressure difference.
pressure difference in groundwater is created by the height difference of the
groundwater table relative to different areas.
of hill the pressure is higher than in lower areas such a stream channel, so the
water will move to the lower pressure areas
(French engineer in middle of nineteenth century)
realized, that if the porosity and permeability remains the same, then the water
moves faster if the slope of the water table is steeper.
slope of the water table is the hydraulic gradient. He defined the
relationship of the velocity of watermovement and height of water table.
V = Kh/l
head (vertical difference between recharge and discharge)
of the flow
relationship between stream and ground water level:
grondw. table is higher than the stream, the stream is supplied from
groundwater!! (humid climate)
water level is lower than the stream (arid climate)
AND ARTIFICIAL DISCHARGE:
table or perched water table intersect with surface, and water will flow out
from the ground. (superstitious people thought that they had power for treating
or drilled openings for water. Most wells have to be pumped to bring water out.
If it is pumped the ground water is lowered around.
CONE OF DEPRESSION. = can cause dry well.
word comes from French town where the first artesian well was drilled. (1126) it
is still flowing.
ground water is confined and build up high hydrostatic pressure (fluid
pressure). If we drill a well into an aquifer like this, the water will flow out
To develop an artesian system there are three geologic factor we need:
aquifer has to be confined (aquiclude above and below, to prevent water from
sequence has to be tilted, which means it has an access to recharge
There is sufficient precipitation to fill the used water.
pressure surface:The surface defined by water table in the recharge area. In any
well the water would rise exactly to the water pressure surface.
tower will make a water pressure surface, that is why water flows freely from
SPRINGS AND GEYSERS
recent active volcanic areas the rocks stay hot for thousands of years. If
groundwater percolate through
rocks are heated and will be hot spring or geysers when returned to the surface.
the hot spring’s heat source is igneous activity, but it can be just deep
water warmed bec. gg.
groundwater percolating down into the fracture network, and becomes heated as it
comes into contact with hot rocks. When the water gets near to its boiling point
, a slight rise in temperature, or a little escaped gas will instantly change
the water to steam. The expanding
steam will rise the water above quickly above the surface. = geyser eruption.
After eruption the new groundwater relatively cold seeps to the system.
in hot springs and geysers!!!!! Treatment.
CaCO3 -- travertino
areas under humid climates!!!!!!
water + carbonic acid
regions where bedrock is limestone the surface can be pitted with numerous
depressions, that vary in size and shape. These depressions are called
1. by the dissolution act of seeping groundwater and rainwater. (gentle sloping crater)
these openings are enlarged and filled by soil.
2. by collapse of cave roof. (steep slope crater) Danger!!!!!!
KARST TOPOGRAPHY (groundwater erosion)
Kentucky, Florida, Virginia
area is characterized by numerous caves, springs, sinkholes, solution valleys,
and dissapering streams. (staining)
streams water flow on the surface for a short distance and disappear in a
Mainly CaCO3: calcite, aragonite
reddish, blacksish, (historic fires)
Lowering water table
groundwater at a higher rate than it is replaced will generally lower the
PLAIN; Nebraska, Kansas, Oklahoma, Texas)
Island (New York, 1960)
groundwater which is less dense than saltwater
lens shaped body above underlying saltwater. The weight of freshwater create a
pressure on the saltwater. If some of the freshwater is removed by pumping it
forms the Cone of depression and it will make
cone of ascension in salty water (salt water starts to go to the well),
so water will be contaminated with salty water. It can be prevented by using
recharge wells in the area.
poorly consolidated sediment groundwater pumping creates sinking of the surface,
because the water had pressure, which kept the pore space in the sediment. (San
Joaquin Valley California Between 1929, 1975 9m of subsidence happened; New
Orleans; Lousiana; Las Vegas 8.5 m). (Tower of Pisa)
FORGET GROUNDWATER MOVES SLOWLY. IT IS HARD TO CLEAN
Non safe disposal of waste material
-sewage (septic tanks)
-toxic disposal sites