Groundwater
BIG Idea:
• Precipitation
and
infiltration
contribute to
groundwater, which is stored in
underground reservoirs until it
surfaces as a spring or is drawn
from a well.
Infiltration:
• process of water
moving into the
soil/ground
• to penetrate,
enter or gain
access
I. Water Beneath the Surface
Groundwater: underground water
that fills almost all of the pores
in rock and sediment
Aquifer: a body of rock that can store
water and also let water flow through
Think of an AQUIFER as a…
• large, horizontal sponge that
absorbs and transports water
along its length
A. Rock Properties that Affect
Groundwater
 Porosity
 Permeability
Porosity: percentage of open
spaces in a rock or sediment
1.
FACTORS THAT INFLUENCE
POROSITY:
(a) SORTING: amount of
uniformity in particle size
HIGH pore space
LOW pore space
(b) SHAPE: rounder particles =
more porous
(c) PACKING: loosely packed =
more porous
2. Permeability: how freely water
flows through open spaces in a
rock (the pores must be connected)
Impermeable – water can NOT flow through
Can something be porous but
impermeable?
• The cork end is red
because the grape
juice went into it.
Does this mean it is
porous?
• If you turn the
bottle upside down
will it leak? Is the
cork permeable?
B. Zones of Groundwater
1. Zone of Saturation: the layer of
ground where all the pores are filled
with water.
2. Water Table: upper surface of
the zone of saturation
3. Zone of Aeration: upper region,
where water is both in the soil and
seeping down to the water table.
Zone of
Aeration
►
• Capillary Action:
ability of water to
rise UP the soil.
•
particle size =
greater capillarity
Smaller
Capillary Fringe: middle layer,
between the water table and the
zone of aeration.
C. MOVEMENT OF
GROUNDWATER
• Depends on:
1. Permeability of the aquifer
• ↑ permeability = ↑ velocity
2. Gradient of the water table
• Gradient = steepness of the
slope
• ↑ gradient = ↑ velocity
II. Wells and Springs
• Water Table: upper layer of rocks
with all pores filled with water.
A. Ordinary Well: A hole dug below
the water table which fills up
with water.
Cone of Depression: lowered area of
the water table due to pumping
B. Artesian Wells: water flows
freely with no pumping
• Underground water
under pressure
(between two
impermeable rock
layers) rises to the
surface
• Water is naturally
filtered as it passes
through porous rock
and seeps to surface
III. Groundwater and
Chemical Weathering
A. Caverns: rocks rich in calcite
(limestone) slowly dissolved by
carbonic acid.
• Hard water = many dissolved
minerals (Ca, Mg, Fe)
• Soft water = few dissolved
minerals
Luray Caverns, VA
• Formation of a Cave
1. Stalactites: water with
dissolved calcite runs from a
cave’s ceiling and solidifies
downward.
2. Stalagmites: calcite rich water
drips on the cave’s floor and
builds upward.
If the two
connect,
then it
forms a
column.
3. Natural Bridge:
when the roof of
a cavern
collapses in
several places
leaving an archshaped rock.
B. KARST TOPOGRAPHY
• regions where chemical weathering
by groundwater is now visible at the
surface
• regions where it is humid and there
are limestone formations near the
surface
• Virginia, Kentucky, Tennessee,
Indiana, and Florida have Karst
Topography
1. Sinkholes (the main feature
of Karst Topography)
How do sinkholes form?
• Rain seeps through soil and absorbs
carbon dioxide and reacts with decaying
vegetation
• Acidic water is created
• Water moves through spaces and cracks
underground
• Limestone is slowly dissolved, creating
network of cavities and voids
• Pores and cracks enlarge
• Land surface above collapses or sinks
2. Streams that disappear in
the ground
Like Lewis Creek in Staunton
3. Caverns and Caves
•