Running Water and Groundwater

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Chapter 6

• Running Water and Groundwater

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Running water

• About 75 percent of the Earth's surface is
  water-covered.
• 97.2 of the water on Earth is salt water
  (oceans) and only 2.8 is fresh water (lakes,
  rivers, streams, groundwater, glaciers, ice
  sheets, and the atmosphere).
• Most human uses, such as agriculture and
  drinking, require fresh water.
• Most of the fresh water, about 77 is frozen
  solid in the icecaps and glaciers.
• Only a tiny fraction of the Earths water supply
  is available for our use.
• 22 of the remaining fresh water is groundwater
  and the other 1 of fresh water is surface water
  in the form of lakes, rivers, soil moisture, and
  atmosphere.

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Running water
4
Running water

• Water constantly moves among the oceans, the
  atmosphere, the solid Earth, and the biosphere.
• This unending circulation of Earths water supply
  is the water cycle.
• This cycle is possible because water readily
  changes from one state (liquid, solid, gas) to
  another at temperatures and pressures common on
  Earths surface.
• Solid A definite volume and shape.
• Exists in oceans, streams, lakes, and aquifers.
• Liquid A definite volume but an indefinite
  shape.
• It takes the shape of its container.
• Exists in glaciers, frozen surface waters, and
  the polar ice caps.
• Gas Neither a definite volume nor a definite
  shape.
• Gases take the shape of their container, but
  their volume changes with changes in pressure and
  temperature.
• Exists in the atmosphere.

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Running water
6
Running water

• In the water cycle, the sun heats the Earth's
  surface water, causing that surface water to
  evaporate (gas).
• Evaporation To convert into vapor.
• This water vapor then rises into the earth's
  atmosphere where it cools and condenses into
  liquid droplets.
• Condensation to change from gaseous state to
  liquid state.

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Running water

• These droplets combine and grow until they become
  too heavy and fall to the earth as precipitation
  (liquid if rain, solid if snow).
• Precipitation Any liquid or solid form of water
  particles that fall from the atmosphere to the
  ground.
• Water is temporarily stored in lakes, glaciers,
  underground, or living organisms.
• The water can move from these places by streams
  and rivers, returns to the oceans, is used by
  plants (transpiration) or animals or is
  evaporated directly back into the atmosphere.
• Transpiration the evaporation of water from
  plant tissues into the surrounding atmosphere.

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Running water

• Some of the water on land slowly soaks into the
  ground through infiltration.
• Infiltration The movement of surface water into
  rock or soil through cracks and pore spaces.
• The water gradually moves through the land and
  actually seeps into lakes, streams, or the ocean.
• When the rate of rainfall exceeds Earths ability
  to absorb it, the excess water flows over the
  surface into lakes and streams in a process
  called runoff.
• Runoff Water that flows over the land surface
  rather than seeping into the ground.

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The water cycle is the

• Distribution of drinking water on Earth.
• Unending circulation of Earths water supply.
• The recycling of water after industrial use.
• The evaporation of water from Earths surface.

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Plants release water into the atmosphere through
a process called

• Evaporation.
• Transpiration.
• Infiltration.
• Precipitation.

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Running water

• Balance in the water cycle means the average
  annual precipitation over Earth equals the amount
  of water that evaporates.
• Examples
• Precipitation exceeds evaporation over
  continents.
• Over oceans, evaporation exceeds precipitation.
• The fact is that the level of world oceans in not
  changing very much indicates the system is
  balanced.

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Running water
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Balance in the water cycle means that

• The average annual precipitation over Earth
  equals the amount of water that evaporates.
• Water that falls to Earth only enters oceans.
• The amount of water that falls to Earth weighs
  the same as the amount of water that condenses in
  clouds.
• Water that evaporates from Earths surface
  remains forever in the atmosphere.

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The average annual precipitation worldwide must
equal the quantity of water

• Evaporated.
• Transpired.
• Infiltrated.
• Locked in glaciers.

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Running water

• Gravity influences the way water makes its way to
  the oceans.
• The time this journey takes depends on the
  velocity of the stream.
• Velocity The distance that water travels in a
  period of time.
• Along straight stretches, the highest velocities
  are neat the center of the channel just below the
  surface.
• The center of the channel is where friction is
  lowest.
• A streams zone of maximum, speed shifts toward
  its outer bank when a stream curves.
• The ability of a stream to erode and transport
  materials depends largely on its velocity.
• Several factors influence the velocity of a
  stream
• Gradient, shape, size, roughness of its channel,
  and its discharge.

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Running water

• Gradient
• The slope or steepness of a stream channel.
• Usually expressed as the vertical drop of a
  stream over a certain distance.
• Gradient varies over a streams length and
  between streams.
• The steeper the gradient, the more energy the
  stream has as it flows downhill.

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Running water
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Running water

• 2. Channel Characteristics
• A stream channel is the course the water in a
  stream follows.
• As water flows, it encounters friction from the
  sides and bottom of its channel.
• The shape, size, and roughness of the channel
  affect the amount of friction.
• Water in a smooth channel flows more easily.
• Larger channels also have more efficient water
  flow because a smaller proportion of water is in
  contact with the channel surfaces.

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Running water

• 3. Discharge
• The volume of water flowing past a certain point
  in a given unit of time.
• Usually measured in cubic meters per second
  (m3/sec).
• Discharges of most rivers change with rainfall
  and snowmelt.
• The size and velocity of the stream also changes
  when discharge changes.
• Building urban centers (urbanization) around a
  stream channel can also affect discharge.
• Ex The magnitude and frequency of floods can
  increase.

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Running water
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The ability of a stream to erode and transport
material depends largely on its

• Width.
• Length.
• Velocity.
• Density.

22
Which of the following factors does not influence
stream velocity

• Channel size and shape.
• Stream gradient.
• Stream elevation.
• Discharge of stream.

23
Along straight stretches of a stream channel, the
highest velocities of water are found in what
part of the stream?

• Near the water surface in the center of the
  stream.
• Near the water surface along the stream banks.
• Along the stream bottom in the center of the
  stream.
• Along the stream bottom near the stream banks.

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The vertical drop of a stream channel over a
certain distance is called

• Discharge.
• Channel roughness.
• Gradient.
• Runoff.

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A streams discharge

• Decreases between its source and mouth.
• Remains the same throughout its course.
• Is greatest during times of drought.
• Increases between its source and mouth.

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Running water

• One useful way to study a stream is to look at
  its profile.
• Profile A cross-sectional view of a stream from
  its source, or headwaters, to its mouth the
  point where the river empties into another body
  of water.
• The most obvious feature of a typical stream
  profile is a decreasing gradient or slope from
  its headwaters to its mouth.

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Running water
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If you were to examine the profile of a typical
stream, you would probably find that the gradient
is

• Steepest near the mouth.
• Steepest near the head.
• About the same at both the head and mouth.
• Gentler near the head.

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Running water

• While gradient decreases between a streams
  headwaters and mouth, discharge increases.
• Discharge increases due to more and more
  tributaries entering the main channel.
• Tributary A stream that empties into another
  stream.
• In humid regions, the groundwater supply adds
  even more water to the channel.
• As the river moves downstream, its width, depth,
  and velocity increase with the increased volume
  of the water it carries.
• The observed increase in the average velocity of
  the water downstream contradicts what people may
  think about mountain streams.
• Although mountain streams may look violent and
  fast, its average velocity is often less than the
  average velocity of a river near its mouth.

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In a typical stream, where the gradient is steep,
the discharge

• Is small.
• Is large.
• Cannot be determined.
• Is very large.

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As stream discharge increases, which of the
following occurs?

• Stream velocity, channel width, and depth all
  increase.
• Stream velocity, channel width, and depth all
  decrease.
• Stream velocity increases, but channel width and
  depth both decrease.
• Stream velocity decreases, but channel width and
  depth both increase.

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Running water

• Streams cant erode their channels endlessly, as
  there is a limit to how deep a stream can erode.
• Base level is the lowest point to which a stream
  can erode its channel.
• The level at which the mouth of a stream enters
  the ocean, a lake, or another stream.
• There are two types of base level
• Ultimate Base Level
• Temporary Base Level

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Running water

• Ultimate Base Level
• Ultimate base level is sea level because it is
  the lowest level that stream erosion can lower
  the land.
• 2. Temporary Base Level
• Includes lakes, resistant layers of rock, and
  main stream that act as base level for their
  tributaries.
• Ex When a stream enters a lake, its velocity
  quickly approaches zero, and thus its ability to
  erode ceases. However, because the outlet of the
  lake can cut downward and drain the lake, the
  lake is only a temporary obstacle to the streams
  ability to erode its channel.

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Base level is

• Any part of the stream that is below sea level.
• The lowest point to which a stream can erode its
  channel.
• The source from which the stream flows.
• The elevation of a streams largest tributary.

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What is the ultimate base level of a stream?

• A large lake.
• The ocean.
• A resistant layer of rock.
• A larger stream.

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Lowering a streams base level will cause the
stream to

• Deposit sediment.
• Meandor.
• Change course.
• Downcut.

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Running water

• A stream in a broad, flat-bottomed valley that is
  near its base level often develops a course with
  many bends called meanders.
• If base level dropped or the land was uplifted
  the river, which is now considerably above base
  level, would have excess energy and would downcut
  its channel.
• The result could be incised meanders a winding
  river in a steep, narrow valley.

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Running water
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The work of streams

• Streams generally erode their channels lifting
  loose particles by abrasion, grinding, and by
  dissolving soluble material.
• The stronger the current is, the more erosional
  power it has and the more effectively the water
  will pick up particles.
• Sand and gravel carried in a stream can erode
  solid rock channels like sandpaper.
• Ex Pebbles caught in swirling stream currents
  can act like cutting tools and bore circular
  potholes into the channel floor.
• Streams transport sediment in three ways
• In solution (dissolved load).
• In suspension (suspended load).
• Scooting or rolling along the bottom (bed load).

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The work of streams

• Dissolved Load
• Most of the dissolved load enters streams through
  groundwater.
• Some through dissolving rock along streams
  course.
• The amount of material in stream is dependent
  upon the climate and geologic setting.
• Usually expressed in parts per million (ppm).
• Ex Some rivers have a dissolved load of 1000
  ppm.
• Average for the worlds rivers is estimated at
  115 to 120 ppm.
• Streams supply almost 4 billion metric tons of
  dissolved substances to the oceans each year.

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The work of streams

• 2. Suspended Load
• Most streams carry the largest part of their load
  in suspension.
• The visible cloud of sediment suspended in the
  water is the most obvious portion of a streams
  load.
• They usually carry only sand, silt, and clay this
  way.
• Streams also transport other materials during a
  flood because of increased water velocity.

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The work of streams
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The work of streams

• 3. Bed Load
• The part of a streams load of solid material
  that is made up of sediment too large to be
  carried in suspension.
• Larger, coarser particles move along the bottom,
  or bed, of the stream channel.
• The bed load only moves when the force of water
  is great enough to move the larger particles.

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The work of streams

• The ability of streams to carry a load is
  determined by two factors
• The streams competence
• The streams capacity.
• Competence
• Measures the largest particles it can transport.
• Increases with velocity.
• When the velocity doubles, the competence of a
  stream increases by a factor of 4.
• 2. Capacity
• The maximum load it can carry.
• Directly related to discharge.
• The greater the volume of water in a stream, the
  greater the capacity is for carrying sediment.

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Most streams carry the largest part of their load

• As dissolved material.
• Along the streams bottom.
• As bed load.
• In suspension.

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The suspended load of a stream

• Is deposited before the bed load.
• Consists primarily of highly soluble substances.
• Moves along the bottom of the channel by rolling
  or sliding.
• Usually consists of fine sand, silt, and
  clay-sized particles.

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The capacity of a stream is directly related to
its

• Velocity.
• Discharge.
• Gradient.
• Meandering.

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What is the measure of the largest particles a
stream can carry?

• Competence.
• Capacity.
• Discharge.
• Gradient.

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The work of streams

• Whenever a stream slows down, the situation
  reverses.
• Velocity decreases competence decreases, and
  sediment begins to drop out (largest particles
  first).
• Deposition occurs as streamflow drops below the
  critical settling velocity of a certain particle
  size. The sediment in that category begins to
  settle out.
• Stream transport separates solid particles of
  various sizes, large to small.
• This process is called sorting.
• The sorted material deposited by a stream is
  called alluvium.
• Many different depositional features are made of
  alluvium.

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The work of streams

• Deltas
• When a stream enters the relatively still waters
  of an ocean or lake, its velocity drops,
  resulting in the stream depositing its sediment
  which forms a delta.
• Delta An accumulation of sediment formed where a
  stream enters a lake or ocean.
• As a delta grows, the streams gradient lessens
  and the water slows down.
• The channel becomes choked with sediment
  resulting in the river changing direction
  searching for a shorter route to base level.
• The stream often divides into several smaller
  channels (distributaries), which act in the
  opposite way of tributaries.
• Distributaries carry water away.

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The work of streams
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The work of streams

• After many shifts, a delta may grow into a
  triangular shape (? Greek letter delta).
• Not all deltas have this ideal shape.
• Differences in the shapes of the shorelines and
  variations in the strength of waves and currents
  result in different shapes of the delta.

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The work of streams

• 2. Natural Levees
• Some rivers occupy valleys with broad, flat
  floors.
• Successive floods over many years can build
  natural levees along them.
• Natural Levee A landform that parallels some
  streams.
• Forms when a stream overflows its banks its
  velocity rapidly decreases and leaves coarse
  sediment deposits in strips that border the
  channel.
• As the water spreads out over the valley, less
  sediment is deposited.
• This uneven distribution of material produces the
  gentle slope of a natural levee.

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The work of streams
55
A depositional feature that forms where a stream
enters a lake or ocean is a (an)

• Natural Levee.
• Delta.
• Meander.
• Oxbow Lake.

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A natural levee is

• An erosional feature perpendicular to the stream
  channel.
• A depositional feature perpendicular to the
  stream channel.
• An erosional feature parallel to the stream
  channel.
• A depositional feature parallel to the stream
  channel.

57
In a stream channel, which of the following will
be deposited first?

• The dissolved load.
• Fine sand and silt.
• Gravel-sized particles.
• Clay-sized particles.

58
Occasionally, deposition causes the main channel
of a stream to divide into several smaller
channels called

• Oxbow lakes.
• Distributaries.
• Meanders.
• Deltas.

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The work of streams

• There are two different types of stream valleys
• Narrow Valley
• A narrow V-shaped valley shows that the streams
  primary work has been downcutting toward base
  level.
• Prominent features are rapids and waterfalls,
  which occur where the stream profile drops
  rapidly.

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The work of streams

• 2. Wide Valleys
• Once a stream has cut its channel closer to base
  level, it starts widening.
• The side-to-side cutting of a stream eventually
  produces a flat valley floor, or floodplain.
• Streams that flow on floodplains move in
  meanders.
• Most of the erosion occurs on the outside of the
  meander often called the cut bank where the
  velocity and turbulence are greatest.
• The debris that is removed is then deposited
  downstream as point bars.
• Point bars form in zones of decreased velocity on
  the insides of meanders.

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The work of streams

• Erosion is more effective on the downstream side
  of a meander because of the slope of the channel.
• The bends gradually travel down the valley.
• Sometimes the movement of a meander slows when it
  reaches a more resistant portion of the
  floodplain, which results in the next meander
  overtaking it.
• The meander is narrowed, and eventually the
  meander is cutoff, and because of its shape, the
  abandoned bend is called an oxbow lake.

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The work of streams
63
The flat portion of a valley floor adjacent to a
stream is called a

• Floodplain
• Meander
• Divide
• Tributary

64
The most prominent features of a narrow, V-shaped
valley, where the stream profile drops rapidly,
are

• Meanders and Floodplains
• Rapids and Waterfalls
• Lakes and Ponds
• Deltas and Natural Levees

65
A floodplain forms where a stream

• Cuts downward rapidly.
• Is far above its base level.
• Carries no bed load.
• Cuts mainly side to side.

66
Which of the following would least likely be
found in a wide valley?

• Oxbow Lake
• Meanders
• Rapids
• A Cutoff

67
What type of stream valley would form in a
mountainous region?

• A wide, flat valley.
• No valley would form.
• The type of valley would depend on the stream
  discharge.
• A narrow V-shaped valley.

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The work of streams

• A flood occurs when the discharge of a stream
  becomes so great that it exceeds the capacity of
  its channel and overtakes its banks.
• Floods are the most common and most destructive
  of all natural geologic hazards.
• Most floods are caused by rapid spring snow melt
  or storms that bring heavy rains over a large
  region.
• Ex Mississippi River Valley, Summer of 1993.

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The work of streams
70
The work of streams

• Flash floods occur with little warning, and they
  can be deadly as walls of water sweep through
  river valleys.
• Several factors influence flash floods
• Rainfall intensity/duration.
• Surface conditions.
• Topography.
• Human interference can worsen or even cause
  floods.
• Ex Failure of a dam or an artificial levee.
• There are several flood control strategies
• Artificial levees.
• Flood control dams
• Placing limits on floodplain development.

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The work of streams

• Artificial Levees
• Artificial levees are earthen mounds built on the
  banks of a river.
• They increase the volume of water a channel can
  hold.
• Because the stream cannot deposit material
  outside of its channel the bottom gradually
  builds up, thus it takes less water to overflow
  the levee.
• They are not built to withstand periods of
  extreme flooding.

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The work of streams

• 2. Flood-Control Dam
• Store floodwater and then let it out slowly.
• Since the 1920s, thousands of dams have been
  built on nearly every major river in the U.S.
• Dams are not built to last forever, as sediment
  builds up behind the dam, and stored water will
  gradually diminish.
• Large dams also cause ecological damage to river
  environments.

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The work of streams

• 3. Limiting Development
• Many scientists and engineers advocate sound
  floodplain management instead of building
  structures.
• Minimizing development on floodplains allows them
  to absorb floodwaters with little harm to homes
  and businesses.

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The work of streams

• Every stream has a drainage basin.
• A drainage basin is the land area that
  contributes water to a stream.
• An imaginary line called a divide separates the
  drainage basins of one stream from another.
• Divides range in scale from a ridge separating
  two small gullies on a hillside to a continental
  divide, which splits continents into enormous
  drainage basins.
• The Mississippi River has the largest drainage
  basin in North America.
• The river and its tributaries collect water from
  more than 3.2 million square kilometers of the
  continent.

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The work of streams
76
One major cause of floods is

• Rapid spring snow melt.
• A decrease in stream discharge.
• Light rain over a large area.
• Increased capacity of stream channels.

77
One traditional flood control method has been to
attempt to keep the streams flow within its
channel by creating

• Meanders.
• Artificial Cutoffs.
• Artificial Levees.
• Flood Control Dams.

78
Limiting development on floodplains is effective
because it

• Allows floodplains to absorb floodwaterrs with
  little harm to structures.
• Eliminates wide stream meanders.
• Is more expensive to build structures on flat
  land.
• Helps keep floodwaters within stream channels.

79
A drainage basin is

• The channel of a stream.
• The land covered by floodwaters.
• The land area that contributes water to a stream.
• All stream that flow directly into an ocean.

80
What are the boundaries called that separate
streams in adjacent drainage basins?

• Mountain ranges.
• Divides.
• Valleys.
• Levees.

81
Water beneath the surface

• Underground water in wells and springs provides
  water for cities, crops, livestock, and industry.
• In the U.S., it is the drinking water for more
  than 50 of the population.
• It also provides 40 of the irrigation water and
  more than 25 of industrys needs.
• The amount of water that seeps or soaks into the
  ground depends on the steepness of slopes, the
  nature of surface materials, the intensity of
  rainfall, and the type and amount of vegetation.

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Water beneath the surface
83
Water beneath the surface

• Some of the water that soaks into the ground does
  not travel far as molecular attractions hold it
  in place as a surface film on soil particles.
• This near surface zone is called the belt of soil
  moisture.
• Roots, voids left by decayed roots, and animal
  and worm burrows criss-cross this zone and help
  rainwater seep into the soil.
• Much of the water in soil seeps downward until it
  reaches the zone of saturation.
• Zone of saturation the area where water fills
  all of the open spaces in sediment and rock
  (groundwater).
• The upper limit of the zone of saturation is the
  water table.
• The area above the water table where the soil,
  sediment, and rocks are not saturated is the zone
  of aeration.
• Water can only be pumped from the zone of
  saturation.

84
Water beneath the surface
85
Water beneath the surface

• The flow and storage of groundwater vary
  depending on the subsurface material.
• The amount of groundwater than can be stored
  depends on porosity.
• Porosity The percentage of the total volume of
  rock or sediment that consists of pore spaces.
• Rock or sediment may be very porous and still
  block waters movement.
• The permeability of a material is its ability to
  release a fluid.
• Groundwater moves by twisting and turning through
  interconnected small openings.
• The groundwater moves more slowly when the pore
  spaces are smaller.
• Example Clay has high porosity, but is
  impermeable because its spaces are so small that
  water cant move through them.

86
Water beneath the surface
87
Water beneath the surface

• Impermeable layers that get in the way or prevent
  water movement are aquitards.
• Permeable rock layers or sediments that transmit
  groundwater freely are aquifers.
• Aquifers are the source of well water.
• Aquifers usually consist of rocks, sand, and
  gravel with a lot of air spaces in which water
  can accumulate.
• Aquifers continuously receive water that
  percolates down from the surface, but this
  process is very slow.
• It may take millions of years for a large aquifer
  to form.
• The area of land from which the groundwater
  originates is called its recharge zone.

88
Water beneath the surface

• The Ogallala Aquifer is the largest underground
  water source in the United States.
• It holds about 4 quadrillion liters of water,
  which is enough to fill Lake Huron (one of the
  five Great Lakes).
• But water from the Ogallala is being removed 10
  to 40 times faster than it is being replenished.
• Most of the water is withdrawn to irrigate crops.

89
Groundwater is found underground in the zone of

• Aeration.
• Soil.
• Saturation.
• Sediment.

90
Permeable rock layers or sediments that transmit
groundwater freely are called

• Aquifers.
• Aquitards.
• Caverns.
• Springs.

91
The percentage of the total volume of rock or
sediment that consists of pore spaces is called

• Permeability.
• An aquifer.
• The zone of saturation.
• Porosity.

92
Which of the following is a measure of a
materials ability to transmit fluids through
interconnected pore spaces?

• Capacity.
• Competence.
• Permeability.
• Porosity.

93
Water beneath the surface

• A spring forms whenever the water table
  intersects the ground surface.
• Spring a flow of groundwater that emerges
  naturally at the ground surface.
• Springs form when an aquitard blocks downward
  movement of groundwater and forces it to move
  laterally.
• A hot spring is 6C to 9C warmer than the mean
  annual air temperature where the spring occurs.
• Temperatures usually rise with an increase of
  depth at an average of 2C per 100 meters.
• There are more than 1000 hot springs in the U.S.
• More than 95 of the hot springs in the U.S. are
  in the West.
• The source of heat for most hot springs is
  cooling igneous rock.
• In some places, hot acidic water mixes with
  minerals from adjacent rock to form thick,
  bubbling mineral springs called mudpots.

94
Water beneath the surface
95
Water beneath the surface

• A geyser is an intermittent hot spring or
  fountain in which a column of water shoots up
  with great force at various intervals.
• Geysers often shoot up columns of water 30 to 60
  meters.
• After the jet of water stops, a column of steam
  rushes out usually with a thundering roar.
• Ex Old Faithful in Yellowstone National Park,
  which erupts about once each hour.

96
Water beneath the surface
97
Water beneath the surface

• Geysers occur where extensive underground
  chambers exist within hot igneous rocks.
• As relatively cool groundwater enters the
  chambers, the surrounding rock heats it.
• The weight of the overlying water creates great
  pressure at the bottom of the chamber.
• This pressure prevents water from boiling at the
  normal surface temperature of 100C.
• As the heat makes the water expand, it forces
  some of the water out at the surface which
  reduces the pressure in the chamber and boiling
  point.
• Some of the water deep within the chamber then
  turns to steam and makes the geyser erupt.
• After the eruption, the cycle begins again.

98
Springs form where

• There is no water table.
• Flooding makes stream overflow their banks.
• Groundwater sinks in the soil.
• The water table intersects the ground surface.

99
When groundwater enters underground fractures or
caverns in hot igneous rocks, where it is heated
to boiling temperatures, what feature can form?

• Spring
• Geyser
• Aquitard
• Sinkhole

100
Water beneath the surface

• A well is a hole bored into the zone of
  saturation.
• Irrigation for agriculture is by far the single
  greatest use of well water in the U.S.
• More than 65 of groundwater used annually.
• The level of the water table can change
  considerably during a year.
• Ex Dry season and wet seasons.
• To ensure a continuous water supply, a well must
  penetrate far below the water table because the
  water table around the well drops whenever a
  substantial amount of water is withdrawn.
• This effect is called drawdown, and it decreases
  with an increase in distance from the well.
• The result of drawdown is a cone of depression in
  the water table.

101
Water beneath the surface
102
Water beneath the surface
103
Water beneath the surface

• Water must be pumped out of most wells, but a in
  a few wells, water rises on its own to the
  surface.
• This type of well is known as an artesian well.
• Artesian Well Any formation in which groundwater
  rises on its own under pressure.
• For this to occur, two conditions must exist.
• Water must be in an aquifer that is tilted so
  that one end is exposed at the surface.
• There must be aquitards both above and below the
  aquifer to stop the water from escaping.
• The pressure created by the weight of the water
  above forces the water to rise when a well taps
  the aquifer.

104
Water beneath the surface
105
Water beneath the surface

• As with many valuable natural resources,
  groundwater is being threatened at an increasing
  rate.
• Overuse and contamination threatens groundwater
  supplies in some areas.
• In some areas the amount of water available to
  recharge an aquifer is much les than the amount
  being withdrawn.
• Even if pumping were to stop now, it would take
  thousands of years for the groundwater to be
  fully replenished.
• Also, the ground may sink when water is pumped
  from wells faster than natural processes can
  replace it.
• As the water is withdrawn, the ground subsides
  because the weight of the overburden packs
  relatively loose sediment grains more tightly
  together.
• Ex San Joaquin Valley of California.

106
Water beneath the surface
107
Water beneath the surface

• Common sources of groundwater pollution are
  sewage from septic tanks, farm wastes, and
  inadequate or broken sewers.
• If sewage water that is contaminated with
  bacteria enters the groundwater system, it may
  become purified through natural processes.
• The harmful bacteria can be mechanically filtered
  by the sediment though which it passes
  (sandstone), destroyed by chemical oxidation,
  and/or assimilated by other organisms.
• For purification to occur, the aquifer must be of
  the correct composition.

108
Water beneath the surface
109
Water beneath the surface

• Other sources of contamination include
  fertilizers, pesticides, highway salt, and
  chemicals/industrial materials.
• In coastal areas, heavy use of groundwater can
  deplete aquifers, causing underground saltwater
  to enter the wells.
• Once the source of contamination has been
  identified and eliminated, the most common
  practice is to abandon the water supply.
• This allows pollutants to flush out gradually.
• To speed up the process, engineers can pump out
  and treat the polluted water, which then allows
  the aquifer to replenish itself with fresh water.
• Prevention is the most effective solution to
  groundwater contamination.
• Some substance in water are natural (ex calcium
  and iron) which make some water hard.
• Hard water forms scum with soap instead of suds.
  It can also deposit residue that clogs pipes. It
  is generally not a health risk.

110
Water beneath the surface
111
Water beneath the surface
112
Which of the following is not a major source of
groundwater pollution?

• Sewage.
• Compost.
• Pesticides.
• Industrial chemicals.

113
Any formation in which groundwater rises on its
own under pressure is a (an)

• Aquifer.
• Artesian Well.
• Cone of Depression.
• Hot Spring.

114
The depression often produced in the water table,
when water is pumped out of a well, is called

• A perched water table.
• An aquitard.
• The aquifer cone.
• The cone of depression.

115
Groundwater contaminated by sewage from a
ruptured septic tank can sometimes be naturally
purified by flowing for a relatively short
distance through a

• Sandstone aquifer.
• Fractured limestone aquifer.
• Cavernous limestone aquifer.
• Spring where the water table intersects the
  ground surface.

116
Water beneath the surface

• The most spectacular results of groundwaters
  ability to erode rock are limestone caverns.
• A cavern is a naturally formed underground
  chamber.
• Formed when water is slightly acidic (carbonic
  acid), which erodes limestone easily.
• There are thousands of caverns in the U.S.
• Ex Carlsbad Caverns in southeastern New Mexico.

117
Water beneath the surface

• Erosion forms most caverns at or below the water
  table in the zone of saturation.
• The features that produce the greatest curiosity
  for most cavern visitors are depositional stone
  formations.
• They form from seemingly endless dripping of
  water over great spans of time.
• The calcium carbonate left behind produces
  limestone we call travertine.
• These cave deposits are commonly called
  dripstone.

118
Water beneath the surface

• The most familiar dripstone features are
  stalactites.
• Stalactites are icicle-like stone pendants that
  hang from the ceiling of a cavern.
• Formed from the calcite left behind as the water
  drops fall.

119
Water beneath the surface

• Stalagmites are formations that develop on the
  floor of a cavern and reach up toward the
  ceiling.
• Formed when water falls from the ceiling and
  splatters over the surface of the floor, leaving
  behind calcite.
• They are usually more massive and more rounded on
  their upper ends than stalactites.

120
A cavern is an underground chamber formed by

• Erosion
• Deposition
• Evaporation
• Runoff

121
Which of the following statements is true about
stalactites?

• They hang from the ceiling of a cavern.
• They grow up from the floor of a cavern.
• They are the same as stalagmites.
• They either hang from the ceiling or grow up from
  the floor of a cavern.

122
Caverns most commonly form in what type of
bedrock?

• Granite
• Sandstone
• Limestone
• Shale

123
What does groundwater naturally contain that
allows it to dissolve limestone and form caverns?

• Hydrochloric acid
• Sulfur acid
• Carbonic acid
• Nitric acid

124
Water beneath the surface

• Many areas of the world have landscapes that have
  been shaped largely by the dissolving power of
  groundwater.
• These areas are said to have Karst Topography.
• Karst landscapes occur in many regions underlain
  by limestone.
• Karst regions usually show a lack of surface
  drainage (streams).
• If there is a stream, they are usually short.
• Karst areas typically have irregular terrain,
  with many depressions called sinkholes.
• Sinkhole A depression produced in a region where
  groundwater has removed soluble rock.
• Sinkholes form in one of two ways
• Develop over many years without any physical
  disturbance to the rock.
• Shallow and gentle slopes.
• 2. Form suddenly when the roof of a cavern
  collapses.
• Steep-sided and deep.

125
Water beneath the surface
126
Which type of rock usually underlies a karst
landscape?

• Limestone.
• Granite.
• Basalt.
• Shale.

127
Sinkholes can form when

• Rainwater containing carbon dioxide dissolves
  underground rock.
• Minerals dripping from a cavern ceiling form
  stone pendants.
• Streams drop sediment as they enter lakes.
• The water table rises due to flooding.

128
Which of the following is associated with areas
of karst topography?

• Sinkholes
• Sinking streams
• Caverns
• All of the above

129
Which of these landforms is not common in an area
of karst topography?

• Sinkholes.
• Caverns.
• Stalagmites.
• Surface drainage systems.