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Groundwater: Outline1. Groundwater intro and activity

2. Water table and groundwater flow

3. Darcy’s Law and the driver for groundwatermovement

4. Groundwater storage: aquifers & aquitards

4. Groundwater problems (e.g., contamination, pumping, etc.)

Problems Associatedwith Groundwater

• Overuse• Subsidence• Contamination

- Salt water intrusion- Hard water, pollutants

Others? Hazel Landslide

Drawdown due to Over Pumping Friday’s in-class activity

If pumping > recharge

Subsidence due to groundwater withdrawal in Pahrump Valley, Nevada

If pumping > recharge

Subsidence due to groundwater withdrawal in Pahrump Valley, Nevada

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If pumping > recharge

Subsidence due to groundwater withdrawal in Pahrump Valley, Nevada

If pumping > recharge

Subsidence due to groundwater withdrawal in Pahrump Valley, Nevada

If pumping > recharge

Subsidence due to groundwater withdrawal in Pahrump Valley, Nevada

If pumping > recharge

Subsidence: when water is removed, sediment compacts, lowering ground surface.

San Joaquin Valley subsidence

DenverBasin

Aquifers

Barkmann, 2004

As of Feb 2001:~34,000water wells were drilled in the Denver Basin

Non-renewable (?) resource

Denver BasinCross Section

West East

Barkmann, 2004

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Ogallala Aquifer: Largest in the U.S.

First used for irrigation in the late 1800s

1950s: large-scale exploitation

Today: ~170,000 wells used for irrigation

Water table ~200’ lower in some areas!

Ogallala Water Supplies and Usage

Thickest in northMore rain in east Water table decline greatest in south (Kansas & Texas)

17.11.b-c

Water Quality and Groundwater Movement

Groundwater ContaminationSources:

Pesticides/herbicides/fertilizers

Landfill pollutants

Sewage

Acid mine drainage

Radioactive waste

Oil and gasoline

Salt water intrusion

Saltwater Intrusion

Question: Why is ground water flow direction changing here?

A) Pumping lowers water table so that it is tilted towards community well

B) Bacteria expand and push water away from septic tank

C) Drought causes water tableto become lower

D) Septic wastes always flowtowards wells open to the air

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Problems Associatedwith Groundwater

• Overuse• Subsidence• Contamination

- Salt water intrusion- Hard water, pollutants

Others? Hazel Landslide

The Hazel LandslideDéjà vu all over again

1967 slide

2006 slide

From Miller and Sias, 1998 and ppt by Miller ca. 2007

N. Fork Stillaguamish River

On March 22, 2014, a major landslide occurred near Oso, Washington. Death toll currently at 30, with 15 still missing.

Before and After Swipehttp://bit.ly/PeN1JT

1947 1955 1965

19701976 1984

19911995

Meters

0 500

N

2006

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2014 slide breakaway scarp

Harvest on Whitman Bench

Harvest of Headache Creek Basin

Toe Protected

Harvest on Whitman Bench

Figure 1. 3. A conceptual model of groundwater flow to the Hazel landslide.

Figure 3.7. Sensitivity to cutting of the landslide toe by the Stillaguamish River. The heavy line shows the limit of bank cutting imposed for the calculation. Again, grid cells having a factor of safety of 1.3 or greater in the least stable case are left uncolored. Heavy brown lines indicate approximate locations of landslide activity seen in the 1991 photographs (Figure 1.4).

Depth to slip-surface for factor of safety of 1.3.This figure illustrates the potential effects of further destabilization of the landslide. Progressive failure and unloading of the toe of Whitman bench could initiate movement of a vast volume of material,

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