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