A few more words on Humidity
• Dewpoint is defined as the temperature to which air
must be cooled for water condensation to begin, i.e.
for air to become saturated with water vapor.
• At dewpoint temperature, the amount of water vapor
present in the air e is equal to the maximum amount
of vapor air can hold esat at that temperature.
• The capacity of air to hold water vapor is strongly
dependant on temperature; warmer air can “carry’
more vapor.
In other words
• If you know from your measurements the
dew point temperature, you really know
how much water vapor e is in the air.
• The dew point is the temperature when
that much moisture is the most that air can
carry.
• The vapor pressure e is just the saturation
vapor pressure es at the dew point
temperature.
A useful relation
• This means that if we have some expression, or table,
for determining esat at some temperature T, we can also
calculate e by using the dewpoint temperature Td for T
• Dew Point Temperature (Td) describes the actual
amount of water vapor (e), which is the saturation value
es at dew point temperature.
http://cires.colorado.edu/~voemel/vp.html
Freshwater Systems
Streams account for 85% of
sediment transport to the
oceans, glaciers 7%, waves
1.5%, wind 1%
Lab Hose, sand in beaker
Fluvial (Latin fluvius: river)
Lacustrine (lake)
Sources of Earth’s water
(saltwater)
freshwater
Longitudinal profile of a
stream Tributaries
Drainage Divide
Stream capture,
decapitation
Trunk Stream
Distributaries
And Delta
Stream Changes
• Changes from upstream to downstream
• Factors that decrease downstream
– A. Longitudinal Profile is a side-view of a
stream
• From head (headwaters) to mouth of
stream profile flattens out
So gradient (slope) decreases downstream
– B. channel roughness (grain size) also
decreases downstream
• Factors that increase downstream
until the delta
– A. Discharge
– B. Channel size
Base Level
• Elevation below which a stream cannot
erode
• Local and ultimate
• Ultimate usually
~ sea-level
• h=0
A waterfall results from change
in local base level
Local change in base level affects river profiles
Graded Streams
• Erosion and Deposition Equal
• When local conditions in a graded stream
are disrupted, velocity changes.
http://h2o.enr.stat
• Original conditions are restored. e.nc.us/nps/What
_is_NPS/agr.htm
• DEMOS
• Pinched hose demo, change in velocity at restrictions
• Hose and sand demo: faster water is better at erosion
More important definitions
Stream - Sediment Terminology
• Transported material is called load
• Types of load
– Dissolved load - ions in solution
– Suspended load - fine clays, etc
– Bed load Moves during flood - high velocity
Sandy Portion – Saltation (bouncing)
Boulders – Traction (rolling)
• Capacity –maximum load stream transports
• Competence – Largest particles it can move
• Proportional to velocity squared
Suspended load - confluence Green & Colorado Rivers in Canyonlands, Utah
•
Competence
• Maximum particle size a stream transports
• Proportional to velocity squared –K.E.
velocity, increase
Deposition of sediment by a stream Increase
transport and erosion for a
Caused by a decrease in velocity
Competence is reduced
Sediment begins to drop out
particle size
Increase particle size,
increase deposition for a
particular velocity
• 1. Narrow valleys uplift or drop in base level
• V-shaped
• Downcutting toward base level
• Can include rapids and waterfalls
•
•
Straighter streams
Typical of steep slopes in
uplifted areas
An Alluvial Fan in Death Valley
Sudden drop in competence
Alluvial fans
Develop where a
high-gradient
stream leaves a
narrow valley and
spreads out onto
a broad plain
Slopes outward
in a broad arc
2. Wide valleys – high suspended load
–Meanders "Meandering Stream"
• Cut bank and point bar
• Cutoffs and oxbow lakes
–
•
•
Floodplains, either:
Erosional floodplains
Depositional floodplains
The Water Icosahedron
• Water molecule like Mickey Mouse—two positively charged
Hydrogens, one negatively charged oxygen, very polar
molecule, good solvent. Angle about 105o
• Hydrogen bonding, two oxygens share a proton H+ in liquid
water. Arrangement the water icosahedron Top Left
• Hydrogen bonding increases the energy required to vaporize
water. About 585 calories/gram water is released to
atmosphere during condensation.
Erosion and deposition along
a meandering stream
Discussion: Crack the whip
Floodplain
Levee
Meanders get more extreme with time. Deposition at point bar keeps up with erosion at cutbank
• Deposition of sediment by a meandering
stream
• Channel deposits
– Point bars cover bed load as meandering
stream’s channel loops move
–
Floodplain deposits cover point bar
Natural Levees
Natural Levees
–form parallel to the stream
channel, by successive
floods over many years.
Water overtops bank and
slows over floodplain,
competence drops,
deposition occurs.
• This 700 ft section of levee slid into the east side of the
Mississippi River on August 23, 1983 at Darrow, in Ascension
Parrish, Louisiana. The slide occurred shortly after a high water
stage had receded, suggesting that toe undercutting and
rapid drawdown likely contributed to the failure.
Formation of natural levees by flooding
Meandering Stream
Flood over banks, sediment carrying water into wide area, greater drag, lower velocity, load drops
Channel moves in direction of cutbank
Pointbar advances as crossbed drapes
Meandering
Stream
Cut off loops silt up; called oxbow lakes
Old cut-off loop fills with
mud, an oxbow lake
OxBow
Floodplain
http://hays.outcrop.org/gallery/rivers/arid_meander?full=1
Point Bar Sequence from Meandering Stream
Fines of Floodplain
Crossbeds of Point Bar
Gravel of bed
Erosion
• Incised meanders
Delaware Water Gap
• Meanders in steep, narrow valleys
– Caused by a drop in base level or uplift of region
Stream Terraces
River meanders across
floodplain.
Base level drops,
or region uplifts.
River cuts into bed, cutoffs
abandon large loops,
leaving oxbows
Stream less wide, uses
narrower floodplain
Old floodplain is a terrace
A flight of river terraces
3. Braided Streams
• Occur where bed load is very high. Often
big boulders in the stream. At headwaters
and near glaciers
• Many channels because flow is
intermittent/seasonal - old channel banks
collapse in dry season , redirect flow next
flood season
• "mid-channel bars" between channels
Deltas
• Occur where stream hits slow water
• Velocity, competence, bedload drop
• Deposits build out into lake or sheltered
sea, extending the length of the river
• Consists of three types of beds
Topset beds
Foreset beds
Bottomset beds
Deltas have strata deposited in a characteristic geometry
Topsets, Foresets and Bottomsets
Actually much more complex: many distributary channel deposits
River delta distributary channels change location with time
General trend: Delta builds Seaward.
If Floodwaters happen to reach
the sea via a new shortcut, they flow by
the shorter (steeper) path cutting a
new channel, abandon old
A fan-delta in a lake
Part 2 - Groundwater
• water found in sediment, plus
narrow fractures in bedrock
• Groundwater is the largest usable
reservoir of fresh water available to
humans, but much more in glacier ice
Distribution of Groundwater
•Water table is the
upper limit of
saturation
•Variations in the
water table
Depth is
highly
variable
•Varies
season
ally and
from
year to
year
•Shape is
usually
similar to
surface
topography
Groundwater table
generally follows topography
Factors influencing movement of
groundwater - 1
• Porosity – Volume of Pore Space
• Permeability – the ability of a material
to transmit a fluid through pore space
Factors influencing movement of
groundwater - 2
• Aquifer – a permeable rock layer or a
sediment that transmits groundwater
freely (such as sands and gravels)
• Aquitard – an impermeable layer that
hinders water movement (such as
mudstone - clay)
• Aquiclude (Aquifuge) solid,
impermeable rock.
Springs may result from a perched water table
Rollie’s Well
Aquifer
GEYSERS
•Intermittent hot
springs
•Water erupts with
great force
•Occur where
extensive underground
chambers exist near
hot igneous rock
•Groundwater heats,
expands, changes to
steam, and erupts
Yellowstone Geyser erupting
Wells
To obtain a continuous supply of water, we must
place a well below the water table
Sometimes a pump is not needed
Demo: Artesian
Discussion:
Quicksand
Hydraulic head and urban water supplies
Just
Towns
like an
pump
artesian,
the water
savesupmoney
to their water tank at night, when
electricity is cheap. Artificial artesian.
Excessive Pumping of wells can cause
Drawdown (lowering) of the water table
Cone of depression in the water table
May cause dry well
Discharge exceeds
recharge
Saltwater contamination due
to excessive well pumping
Wildwood Crest
Well design requires knowledge of local geology
Don’t fire the town engineer!
Geologic work of groundwater
• Acidic groundwater dissolves limestone
• Groundwater is often mildly acidic
– Contains weak carbonic acid, H2CO3 which
forms when carbon dioxide from the air dissolves
in cloud water droplets
– Groundwater becomes more acidic from
decaying plants "Humic Acid"
• Acid dissolves calcite in limestone, releasing
CO2 gas
CaCO3 + 2H+ ↔ Ca++ + H2O + CO2 (g)
The reaction reverses, and calcite is deposited, if CO2 gas concentration gets high
Geologic work of groundwater
• Caverns
• Features found within caverns
– Composed of dripstone (travertine)
• Calcite deposited as dripping water
evaporates
• Includes stalactites (hanging from the
ceiling) and stalagmites (form on the floor of
a cavern)
CaCO3 + 2H+ ↔ Ca++ + H2O + CO2 (g)
Reaction reverses, and calcite is deposited, if CO2 gas concentration gets high
– Sinkhole or sinks (formed by
groundwater slowly
dissolving the bedrock often
accompanied by collapse)
– Disappearing (aka sinking)
streams
Karst Topography
Stream incision, cave
development and karst
topography
In Xanadu did Kubla Khan
A stately pleasure-dome decree:
Where Alph, the sacred river, ran
Through caverns measureless to man
Down to a sunless sea.
Xanadu, by Samuel Taylor Coleridge
Solution and Collapse Sinkholes
Winter Park, Florida. 1981
Porsche Dealership and Pool
Don’t fire the town’s engineer!
Water weighs 8.34 pounds per gallon,
and is incompressible
Limestone weighs 5744 pounds/ m3
Foghorn Leghorn
Pool 50x25x2 meters