This Week (and next) Today: –Finish Floods –Groundwater Friday: Glaciers.
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Transcript of This Week (and next) Today: –Finish Floods –Groundwater Friday: Glaciers.
This Week (and next)
• Today: – Finish Floods
– Groundwater
• Friday: Glaciers
Finally, a flood of possibly mythic proportions
• “Noah’s Flood” hypothesis• William Ryan & Walter Pittman
(Columbia U.)• Controversial, not universally
accepted, but intriguing
Noah’s Flood
• Coming out of last ice age ~7600 years ago (=5600 B.C.), sea level was low but rising– Why?
• Black Sea was freshwater, surrounded by farms
Noah’s Flood
• Rising global sea level raised Mediterranean above the Bosporus Strait– Broke through natural dam– Water rose ~6 inches / day– Flooded lakeshore communities
some Noah’s Flood evidence
• Many cultures have a flood story, many can be traced to the Black Sea area
• Remains of houses & villages have been found on the pre-flood lakeshore
• But: New work finds no evidence for a sudden rise in water level of Black Sea.
Noah’s Flood• More info:
– book: “Noah’s Flood: The new scientific discoveries about the event that changed history”, Ryan & Pittman, 1998, Simon & Schuster
Today’s Plan: Groundwater
• aquifer / aquitard
• water table
• groundwater flow
• groundwater contamination
Groundwater: aquifers
• Any geologic unit through which water can move easily (i.e. it’s permeable)(= high permeability)
• Porosity: how much water a geologic material can hold
Opposite of an aquifer?
• Aquitard / aquiclude– retards the flow of groundwater (it’s
almost never really zero
Groundwater: aquifers• What would be the properties
(porosity/permeability) of conglomerate?
• High porosity, high permeability
Groundwater: aquifers• What would be the properties
(porosity/permeability) of unfractured granite?
• Low porosity, low permeability
Groundwater: aquifers• Can you think of a rock/sediment
with high porosity and low permeability?
Groundwater: aquifers• Can you think of a rock/sediment
with low porosity and high permeability?
discharge=2000 ft3/s
discharge=4000 ft3/s
How is this possible?
No tributaries
here
Ground Water and Surface Water
• These are almost always connected• If a stream contributes water to the
aquifer it’s called a “losing stream”• If a stream receives water from the
aquifer it’s called a “gaining stream”• Same stream can be both at different
places or at different times
Pumping Animation
• Go to animation at: http://almandine.geol.wwu.edu/~dave/courses/2003/spring/101/lectures/water_level.swf
Your WarmUp AnswersPart B: Pumping wells
• That was a really cool animation but I just don’t understand what is happening.
• Let’s look at the situation again… go!
Your WarmUp AnswersPart B: Pumping wells
• In the low permeability case the water is pumped primarily from the area directly around the well, whereas with the higher permeability the water seems to be drawn from a more broad area surrounding the well "hole". Since permeability refers to the ability of a material to let a fluid move through it, the low permeability doesn't allow the water to venture far from the path of pressure change (the "hole" of the well).
• What happens when this well is heavily pumped?
Pollution of Groundwater
• Need a sense of ground water flow– warmup responses to The velocity of
groundwater flow is dependent on:
porosity and permeability 28%
permeability and hydraulic gradient 61%
porosity and hydraulic gradient 7%
pressure gradient 4%
Groundwater Flow
• Groundwater velocity– Depends on permeability and hydraulic
gradient (slope of water table)– Ranges from 100 m/day to mm/day– A good round number: 1 ft/day
• What happens when a new well here is heavily pumped?
Flow direction
can change