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Water
Terms
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Porosity vs. Permeability
 The terms porosity and permeability are related.
 Porosity is a measure of the amount and size of pore
space within an earth material, such as soil, clay, gravel,
silt, rock, etc.
 Some rocks and soils are very porous, while others have
very little space between the particles.
 Porosity is how much water a material can hold. It is
usually stated as a percentage of the material’s total
volume.
Porosity vs. Permeability
 Permeability is a measure of the ability of an earth
material to let water pass through it.
 Permeability is affected by the size of the particles and
shape of the spaces between the particles.
 Some materials have many spaces between particles,
while others have virtually no space between particles
and are called impermeable.
Porosity vs. Permeability
 Water flows between the spaces in the material.
 If the spaces are close together, such as in clay based soils,
the water will tend to cling to the material and not pass
through it easily or quickly.
 If the spaces are large, such as in the gravel, the water
passes through quickly.
Percolation and Infiltration
 There are two other terms that are used with water:
percolation and infiltration.
 Infiltration is when the water enters the soil surface
after falling from the atmosphere.
 Percolation is the downward movement of water from
the land surface into soil or porous rock, caused mainly
by gravity.
Particle Sizes And Pore Space:
Groundwater vs. Surface Water
 Groundwater is water that flows through the pores in the
rocks and soil beneath the surface of the ground.
 The groundwater trickles downward until it reaches an
impermeable layer of soil or rock.
 We use wells and springs to pull groundwater back to the
surface to drink.
 Ninety-eight percent of Earth’s available freshwater is
groundwater.
Groundwater vs. Surface Water
 Surface water includes rivers, streams, lakes, ponds,
oceans, and even the water that runs down streets during
thunderstorms.
 Surface water will, unless interfered with, flow downhill
until it reaches a creek or stream. The creek or stream will
eventually feed a river that will flow into the ocean. Along
the way, some water will evaporate back into the
atmosphere and will fall back to the Earth as rain.
 Surface water supplies 80% of the water used on a daily
basis.
Groundwater vs. Surface Water
 Surface water which has not yet
flowed into a creek is called
runoff. Bare ground allows a
great deal of runoff to occur.
Plants and dug ponds (a small,
shallow pond created artificially
by digging a depression in the
land) reduce the amount of
runoff.
Watershed Diagram
Watershed vs. Aquifer
 A watershed is an area of land where all of the surface
water within a specified area drains downward and
flows to the same place.
 Each drainage basin, or watershed, is separated
topographically from adjacent basins.
Aquifer
 An aquifer is a natural, underground area where large
quantities of ground water fill the spaces between rocks
and sediment and accumulates.
 This water is available for use by using wells to pump out
the water.
Texas Aquifers
 The state of Texas has 23 aquifers that cover
approximately ¾ of the state.
 The Ogallala Aquifer accounts for about 90%
of the water in all of Texas aquifers.
 Groundwater from Texas aquifers is used
for irrigation, city use, manufacturing, and
livestock production.
 Pumping water from many aquifers in Texas
has resulted in a significant lowering of the
water table.
A map showing watersheds in Texas
More about Aquifers
 Less permeable rock below an aquifer that keeps
groundwater from draining away is called a confining layer
or aquitard.
 The water table in an aquifer is at the very top of the zone
of saturation.
 The zone of saturation is where water completely fills all
the interconnected pore spaces.
Water Table
 The water table is the upper
surface of ground water below
which the soil or rocks are
permanently saturated with
water and where the pressure of
water in the soil equals the
pressure of the atmosphere.
 The water table fluctuates
both with the seasons and
from year to year because it is
affected by climatic variations
and the amount of
precipitation used by
vegetation. It also is affected
by withdrawing excessive
amounts of water from wells.
Pollution
 Pollution is the introduction of a contaminant into the
environment.
 It is created mostly by human actions, but can also be a
result of natural disasters, such as flooding.
 Pollution has a harmful effect on any living organism in
an environment, often making it impossible to sustain
life.
 Pollution to drinking water can cause diseases.