subtitle
Hydrology...an Introduction to
Groundwater & Surface Water
1st – General Perspective on the
Hydrosphere
2nd – Groundwater
3rd – Surface water
General Perspective on the
Hydrosphere
Classroom Resources
Animation “draining the
oceans” giving a feel
for water in the
oceans – largest
water reservoir
Cryosphere – 2nd
largest reservoir
of water on Earth
Groundwater Focus
Although groundwater is
not very globally significant
in volume, it is a critical
source of domestic water,
because it is part of the
limited budget of fresh
(non-saline) water.
It can be viewed as a
partially-renewable
resource:
It is possible to withdraw it
faster than nature
recharges it.
Simplified Hydrologic Cycle
Hydrological Cycle: More Detail
Classroom Resource
WHY HYDROLOGY IS IMPORTANT
• Of total world water, 97.5% is salty water and only 2.5% is
freshwater of which useable freshwater accounts for about 0.5%
• Of the 0.5% useable freshwater, irrigation accounts for 70%, industry
20% and household 10%
• Demand for and use of freshwater has tripled over the past half
century, as world population has grown from 2.5 to 6.45 billion people
• By 2025 global water needs will increase with 40% more required for
cities and 20% for growing crops
• The satellite photos show major freshwater depletion taking place on all
continents, notably in the Dead Sea, the Aral Sea, Lake Chad, the
Mesopotamian Marshlands, the Everglades and other water sources
• According to UNESCO estimates, by 2030 global demands for fresh
water will exceed the supply with potentially disastrous consequences
Sources: Asian Development Bank; BBC; Earth Observatory; UNEP; UNESCO
WHY HYDROLOGY IS IMPORTANT
• Water withdrawals are causing major rivers—such as the Colorado, the
Nile, the Yellow Rivers—to run dry in sections, lakes to vanish and
groundwater tables and aquifers to drop in many places
• Over the next 20 years, average water supply per person is estimated
to drop by a third, potentially endangering human health, agriculture and
the environment
• Water volume in the Aral sea has dropped by about 80% since 1960s,
due to extensive irrigation primarily for cotton production
• Current water levels in Lake Victoria are below normal and the lowest
level since September 1961
• In 2002, around 3.16 billion people (82%) in the Asia Pacific region had
access to improved water supplies, up from 74% in 1990
• Water pollution is a serious threat to the world’s water supply
Sources: Asian Development Bank; BBC; Earth Observatory; UNEP; UNESCO
Groundwater
Groundwater & surface water
are a most precious natural
resources.
According to U.S. estimates,
groundwater provides:
• 34% of agricultural use (mostly for
irrigation)
• 40% of the public water supply
withdrawals
• 53% of all drinking water for the total
population
• 97% of drinking water for the rural
population
Introduction to Groundwater
The zone of
saturation occurs
where water
completely fills
the open spaces in
the soil and rock.
The upper limit of
this zone is called
the water table.
The zone above
the water table is
called the zone of
aeration.
How water
gets into the
zone of
saturation
(well water)
Material
saturated with
water lies below
the water table.
The Water Table
Materials that
conduct water
(are porous and
permeable) are
aquifers.
Materials that do
not conduct
water (are wellcemented,
unfractured, etc.)
are aquicludes &
aquitards.
One inch of rain on one acre of ground
results in 27,192 gallons of water (~100,000 L).
Clay-rich sediments tend to be impermeable and retard water flow.
Perched aquifers are common, since the geology of the near-surface can be
fairly complex. Parts of an aquifer can become perched as a result of slight
variations in the clay content of sediments.
Groundwater: aquifers must be
permeable and porous
• Any geologic unit
through which
water can move
easily (i.e. it’s
permeable)
• Porosity: how
much water a
geologic material
can hold
Porosity and Permeability
Porosity: volume proportion made up of voids
Permeability: connectedness of voids, dictating
capacity to transmit flow
Porosity & Permeability for Life
Used in adult demonstration only
Gravel – great aquifer
Permeable & Porous
Opposite of an aquifer?
• Aquitard / aquiclude
Retards or Precludes the
flow of groundwater
– Shale (compressed
mud) is the example
Aquicludes
or Aquitard
Aquifers
Permeability
Groundwater in a Humid Landscape
• Water infiltrating the ground is recharge.
• Groundwater flowing out from the ground is discharge.
• But water moves slowly (typical range 0.1 to 100 m/day)
Characteristic US Aquifers
Great Plains: water derived
from the Colorado Front Range
Atlantic Coast: water moves
through young, poorly
hardened sediment
Basin and Range: waters
concentrate in gravels &
sands of alluvial fans
Great Plains:
Ogallala
Aquifer being
depleted in
most places
as water table
declined 10 to
> 100 ft.
Water Use in the USA
The blue areas had relatively little water withdrawals in 1990.
Animated map (gif)
Will play inside a powerpoint presentation,
showing increasing reliance on
groundwater withdrawal
Natural Recharge
In arid regions, recharge often
through streams
Drawdown through Wells
Whenever water
is withdrawn
from a well, the
water table
around the well is
lowered. This is
called drawdown.
The conical shape
of the drawdown
region near well
has led to it being
called the cone of
depression.
Classroom
Resource
Groundwater Contamination
A. The groundwater
moves too rapidly
through the
cavernous limestone
to be naturally
purified.
B. Groundwater
movement in the
permeable sandstone
aquifer is slow
enough to allow
natural purification.
Flow
direction can
change
What causes
groundwater
contamination?
 Leaky underground
storage tanks
 Poorly constructed
landfills and septic
systems
 Improperly abandoned
mines and wells
 The overuse of
fertilizers, pesticides,
and road salts
 Runoff from livestock
confinement areas
 Careless industrial
and manufacturing
organizations
 From groundwater.org
Subsidence
Land subsidence due to
groundwater
withdrawal in the San
Joaquin Valley of
California began in the
mid 1920’s and locally
exceeded 8 meters (28
feet) by 1970.
Classroom Resource
• Animation illustrating
that groundwater
removal allows grains
to compact, and that
compaction causes
subsidence
• Like squishing a moist
sponge – once the
water is gone, you can
compact the sponge
Arizona Land Subsidence
Aquifers Susceptible
to Subsidence
Groundwater returns to surface
as baseflow to streams (in humid areas)
Perennial is possible, because
Groundwater returns to surface
as baseflow to streams (in humid areas)
Intermittent Streams:
Wet season raises water table so
base flow feeds stream
Groundwater returns to surface as springs
Can return as Artesian Wells
Water flows freely
out of an artesian
well.
Two requirements
must be met:
-The aquifer must
be inclined so that
it is exposed to
recharge.
-The aquifer must
be confined by
aquitards above
and below so the
water does not
escape.
US Southwest has Artesian
Conditions
Online Video Resource on
Groundwater
EPA Lessons
on
Groundwater
Surface Water – starts with
Infiltration capacity (how much rain can
ground absorb before water runs off)
determines what land will look like
HIGH –
water
sinks
in
LOW –
water
runs
off
High infiltration capacity landscapes
look like this:
Water sinks into ground supports plants &
high water table
Low infiltration capacity
Means that water does not sink in, but runs off
and erodes channels (tiny rills to big gullies)
Eroding landscapes from overland
flow starts with RAINSPLASH
Rainsplash ejects particles into flowing
water
Rainsplash Video
•
This is a high-speed video sequence of rainsplash. A single raindrop
impacts dry sand. Time between individual video frames is 1/240th of a
second. The full video sequence is 0.1 seconds in real time. (Prof.
Schmeeckle, ASU Geographical Sciences)
• http://www.markschmeeckle.com/rainsplash.html
Rainsplash puts smaller pieces into
the flow, leaving behind pedastals
Overland flow – then concentrates
into tiny channels to erode rills
Rainsplash
Rill
Larger Rill
Classroom Resource
Experiment showing how overland flow
starts in a desert (near Tombstone, AZ)
Rills
Rills grow into gullies
Low infiltration capacity means that
water runs off quickly into streams
as flash floods
Gypsum Wash – Near Las Vegas, NV
Idiots on parade – or
Stupidity on summer
vacation
Flood deaths – 2nd to
Heat
Why FLASH FLOODS HAPPEN …
1. Intense Rain
2. Low infiltration capacity of ground (so
water sent quickly to streams)
[there is a threshold that will raise water to
point where stream rises quick & floods]
Why FLASH FLOODS HAPPEN …
2. Low infiltration capacity of ground –
means that there is a high “drainage
density” (lots of channels in an area to
feed water to larger streams)
Why FLASH FLOODS HAPPEN …
3. The water collection area combines at
stream junctions at the same time
Why FLASH FLOODS HAPPEN …
4. Worst in slot canyons, where the
increased water makes height rise
quickly
Classroom Resource
Flash flooding movies
Science of
Hydrographs
Q is “Discharge” (cubic volume per second)
Q = width x depth x velocity
Discharge measured at
Gauging Station
Hydrograph – how discharge
changes over time (minutes, hours,
month, year, decade)
Example of response to single storm
Before
Rain
After
Rain &
water
moves
to streams
Water sinks in
so baseflow feeds
streams slowly
Water runs off fast
so stream
discharge rises
fast
Lag time between rain and stream
rising (long in forest & short in
desert or urban)
Floods and Urbanization
Surface runoff vs. Infiltration
Natural land cover vs. Urban area
Classroom Resource
Animation of how
urbanization
changes a
hydrograph –
making a
forested region
behave more
like a desert in
“shedding
water” rapidly
causing urban
flash floods
Classroom Resources
Clips: flash flooding in urban settings
Influent and Effluent
When groundwater flows
into streams they are called
effluent.
When the water table is low,
streams become influent,
and water leaks from the
stream bed into the ground.
- During dry season
- Permanently in deserts
Core Concept in Surface Water
Hydrology: DRAINAGE BASIN
Synonym:
Watershed
Drainage Divide separates basins
The Continental Divide
In North America, the continental divide
separates watersheds that drain to the
west from those that drain to the east
(and the arctic).
Different sizes of drainage basins
Policies need to be different for
different types of drainage basins
Classroom Resource
Animation illustrating Drainage Basin of
Mississippi River (12th order stream)
Airplane Entertainment & Drainage
Patterns
Question: Is the pattern distributary (flow
splits) or tributary (flow combines)?
Distributary:
Delta & Alluvial Fan
Tributary
Distributary: Alluvial Fan, Tibet
Alluvial fan
Distributary
Ganges,
So. Asia
Deltas distributary
Tributary – patterns you see from
the airplane tells you the geology
Radial
Volcano
Out from Center
Dendritic
same rock type
Rectangular
Jointed & faulted
Trellis
Big stream cuts across
anticline folds
Radial – outward from center
Rectangular
Tributary Pattern
Trellis Tributary
Pattern
Dendritic Tributary
Pattern
Online Resources
Watersheds and Hydrologic Cycle
http://serc.carleton.edu/NAGTWorkshops/vis
ualization/collections/watersheds.html
Groundwater Animations
http://serc.carleton.edu/NAGTWorkshops/vis
ualization/collections/groundwater.html
Cryosphere Visualizations (frozen water)
http://serc.carleton.edu/NAGTWorkshops/vis
ualization/collections/cryosphere.html