GEOLOGY 12
SURFACE PROCESSES II
CHAPTERS 14 & 15 NOTES
RUNNING WATER AND GROUNDWATER
Name __________________
WHERE DOES OUR WATER COME FROM?
Water covers 71% of earth
• 97% of planet’s water is salty
• 3% is fresh water
• 2.997% ice caps, glaciers, or deep
• 0.003% usable fresh water
Properties of Water
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2.
Water acts as a solvent for nutrients carried from air to soil, soil to aquifer &
streams, streams to lakes & ocean
Water stores heat to moderate climate, industrial cooling and power plants
Pure water is tasteless and odorless. A molecule of water contains only hydrogen and
oxygen atoms. Water is never found in a pure state in nature. Both groundwater and
surface water may contain many constituents, including microorganisms, gases,
inorganic and organic materials.
THE WATER CYCLE
The energy for the Water Cycle is derived from the sun.
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I. RUNNING WATER
Streams possess both potential energy and kinetic energy. As water moves
downstream, potential energy is converted into kinetic energy. Most of the kinetic
energy is released as frictional heat, but a small amount remains to do the work of
erosion and transportation.
Stream Erosion - Streams carry material eroded from their own channel plus eroded
material added from the drainage basin. Streams erode by:
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Hydraulic Action - The force of running water can set particles in motion. Loose
particles can be lifted by turbulent flow. The higher water velocity, the larger and
greater quantity of particles can be lifted.
Abrasion - Solid particles in suspension and in the bed load can scour the channel.
Bedrock can be eroded and chipped; sediment particles are smoothed and rounded.
Potholes are semicircular holes scoured out in eddy currents by swirling sand and
gravel.
Solution - Some stream channel material is eroded by rock material being dissolved
away. This mechanism is minor compared to the other mechanisms.
Transportation - Movement of sediment from one place to another can be expressed in
terms of capacity and competence.
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Capacity is the maximum load a stream can carry (the amount of material a stream
can carry at any one time), and varies with stream discharge. Discharge depends
on channel depth and width and gradient (steepness).
Competence is the maximum particle size that a stream can move, and is also
determined by the water velocity. Streams transport their load in three different
ways:
1. Dissolved Load - This is material carried in solution. Most dissolved material
comes from groundwater seeping into streams, and is independent of stream
velocity.
2. Suspended Load - Sediment particles can be carried in moving water.
Suspended load typically composes the largest fraction of material transported
by a stream. For a sediment particle to be transported, the water velocity must
exceed the settling velocity of the particle. Coarser material is carried toward the
channel bottom in the zone of highest water turbulence.
3. Bed Load - This consists of particles too large to be kept in suspension. As the
particles move by sliding, rolling, and jumping by short leaps (saltation), they
cause downcutting of the stream channel.
Deposition - Streams ultimately deposit most of the material they carry. Deposition
results from decreasing water velocity or from chemical changes. The coarsest material
is deposited first as water velocity decreases. Stream deposited material is called
alluvium.
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TRANSPORTATION OF SEDIMENT
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DEPOSITION SEQUENCE OF SEDIMENT
CHARACTERISTICS OF STREAMS
BRAIDED STREAMS AND THEIR DEPOSITS
These are streams with channels split into many winding pathways by the deposition of
sediment in the channel. They occur where a stream receives a heavy load and has
variable discharge. (see page 300)
MEANDERING STREAMS AND THEIR DEPOSITS
Meandering stream have a winding course, which can be described in terms of several
important features: (see diagram on next page)
1. Meanders - These are curves in the stream channel formed by any
obstruction to flow. The channel shape is asymmetric, as meanders migrate
out and down a stream valley through erosion/deposition.
2. Cut Banks - These steep channel banks form from erosion at outer edge of
meanders.
3. Point Bars - These bars form from sediment that is deposited on the inner
edge of meanders where water velocity is slow.
4. Oxbow Lakes - These lakes represent abandoned meander loops. When one
meander catches up with another, the narrow neck of land between them can
be cutoff to form a new, shorter channel. Where the lake fills with sediment, it
is called a meander scar.
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OTHER FEATURES ASSOCIATED WITH STREAM DEVELOPMENT
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Flood Plains are formed when the river overflows its banks. It is built of alluvium
deposited by the river during floods. A river has one flood plain and may have one or
more terraces representing abandoned flood plains. Several sets of terraces
represent either successive lowering of the stream's base level or increases in
stream discharge.
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Incised Meanders develop when a stream erodes downward to bedrock. Erosion
creates deep, meandering canyons with no floodplains if there is little lateral
(sideways) erosion, or natural bridges (a span of rock across a stream valley created
by a meander cut-off) if lateral erosion does take place. In order to become incised,
meanders must have been established before the stream began to cut through
bedrock.
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Waterfalls can form where resistant rock units are underlain by non-resistant rock or
where a stream flows over cliffs formed by glaciers or faulting.
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Rapids are typically caused by resistant rock units outcropping in the stream
channel.
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Deltas develop where a stream enters a standing body of water. The sudden
velocity drop causes stream to drop most of its load. This sediment eventually
blocks the channel and stream seeks a new route, developing a network of
distributaries (smaller channels formed by splitting of main channel.
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Alluvial fans develop where a stream gradient changes abruptly, such as at the foot
of a mountain. The sudden velocity drop causes the stream to drop sediment in a
fan-shaped deposit.
MEANDER AND FLOODPLAIN FORMATION
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II. GROUNDWATER
Ground water results from precipitation that sinks into spaces between soil particles.
There is 40x more groundwater than surface water - very unevenly distributed.
Different materials have differing amounts of available pore space.
• pore space - a small to minute opening or passageway in a rock or soil
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permeable - the ability of a porous rock (such as sandstone), sediment, or soil for
transmitting a fluid. (Although limestone does not have any pore spaces it is
permeable due to many cracks and fissures.)
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impermeable - not permitting the passage of a fluid through the pores. (For
example, shale is impermeable because it has few pore spaces, while pumice is
impermeable because it has many isolated pore spaces.)
PORE SPACE: Permeable vs. Impermeable
A.
B.
C.
D.
Figure 1
interlocking crystals (igneous tock)
Î low porosity
well rounded, well sorted (sand,
sandstone) Î porous, permeable
poorly sorted sediments fine grains
fill pore spaces Î less porosity and
permeability
packing of platy minerals (clay, shale)
Î may have high porosity but low
permeability
Figure 2
a.
b.
c.
d.
well rounded particles Î abundant pore space, permeable
poorly sorted sediments Î reduced pore space, less permeable
cemented grains Î reduced pore space, somewhat permeable
cracks and fissures Î variable pore space, permeable
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THE WATER TABLE
Zone of Saturation - all available spaces are filled with water
Water Table - top of the zone of saturation
PERCHED WATER TABLES (see page 321)
The perched water table is located at ______ because…
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Aquifer - A body of rock that can conduct ground water and yields significant quantities
of water to wells and springs (a ground-water reservoir)
Groundwater Depletion - withdrawal exceeds recharge throughout the aquifer
Salt Water Intrusion – ground water depletion in coastal areas (see page 325)
Cone of Depression - localized pumping exceeds rate of recharge. Water table near
well drops. Pollutants tend to flow into cone. (see page 324)
Cone of Depression
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HUMAN IMPACT ON GROUNDWATER
Sources of contamination that can cause groundwater contamination:
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On-site septic systems
Leaky tanks or pipelines containing petroleum products
Leaks or spills of industrial chemicals at manufacturing facilities
Underground injection wells (industrial waste)
Municipal landfills
Livestock wastes
Leaky sewer lines
Chemicals used at wood preservation facilities
Mill tailings in mining areas
Fly ash from coal-fired power plants
Sludge disposal areas at petroleum refineries
Land spreading of sewage or sewage sludge
Graveyards
Road salt storage areas
Wells for disposal of liquid wastes
Runoff of salt and other chemicals from roads and highways
Spills related to highway or railway accidents
Coal tar at old coal gasification sites
Asphalt production and equipment cleaning sites
Fertilizers on agricultural land
Pesticides on agricultural land and forests
Contaminants in rain, snow, and dry atmospheric fallout
ASSIGNMENT:
Reference Pages: Chapter 14 p.292 to 303, 313
Chapter 15 p.318 to 325, 328 to 334
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Chapters 14 & 15 Worksheet
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Water Table Exercise