Groundwater Resources: The Desert Southwest

1. Groundwater Resources: The Desert Southwest

2.

What has happened to groundwater
levels in the area investigated as time
has progressed? What were the
reasons for any changes?

3.

What sources other than agriculture could
be contributing to the decline in
groundwater?
How do these sources use groundwater?

4. Groundwater Depletion

• Regions where groundwater
is pumped faster than it can
be recharged begin to see
effects of groundwater
depletion.
• Many sunny, arid regions
are good for growing crops
as long as water can be
added.
• Groundwater can be used
to increase farming
productivity in regions that
are technically too dry.

5. Agriculture

• Using the maps below, which regions of the United States
would be best for growing crops?

6. Groundwater Depletion

• Agriculture is the main consumer of groundwater in the US.
• Most agricultural land is located in regions that receive less
than 20 inches of rainfall per year.
Cumulative Groundwater Depletion, 1900-2008

7. Groundwater Depletion

• Some aquifers are overused because water is pumped out
faster than it is recharged.
• The water table slowly subsides, requiring wells to be dug
deeper, which takes more money and energy.
• Subsidence: Sinking of the land surface because of the
extraction of groundwater.
• Rule of Capture: A law in some states stating that the first
person to "capture" a resource (groundwater, oil, gas) owns
that resource.

8. Hydrologic Cycle

• Water table: The
“surface” of the
material that is
saturated with
groundwater in a
given vicinity.
How might the lowering of the water table affect other parts of
the hydro-cycle and ultimately affect local ecosystems?

9. Ogallala Aquifer

• The Ogallala Aquifer supplies about
one-third of the irrigation water in the
United States.
• The Ogallala Aquifer is from 30 to 100
meters deep over an area of about
440,000 square kilometers
• The Ogallala filled slowly during the Ice
Age tens of thousands of years ago.
• Porosity: A measure of how much of a
rock, sediment, or soil is open space.
• Permeability: A measure of the ease
with which a fluid (water in this case)
can move through a porous material.

10. Groundwater Depletion

• Where is the Ogallala Aquifer on these maps? Describe the
trends around this aquifer.

11.

What factors can you
attribute to the declining
groundwater from north
to south?
What factors can you
attribute to the
increase (recharge) of
groundwater in blue in
the north and south?

12.

• The Keystone Pipeline currently
sends 590,000 barrels of crude oil
per day to refineries in the United
States.
• In 2011, the Keystone XL pipeline
extension was proposed to
increase production by an
additional 510,000 barrels per day.
• Environmental groups, citizens,
and politicians have raised
concerns about the potential
negative impacts of the Keystone
XL project and have delayed its
construction.
What negative impacts
might these groups be
concerned about?

13. Solutions for Groundwater Depletion

• What are some ways to reduce groundwater
depletion?
• Conserving water in urban areas.
– reducing lawn watering
• Desalinating brackish water or seawater.
• Promote groundwater banking — Excess surface water (from
floods, drainage, state and federal water projects) is pumped into an
aquifer and then removed during droughts.
• Understand the water footprint of the food we eat.
Given what you know about your water footprint and agriculture,
is it reasonable to say that reducing your personal water use will
help with water scarcity in the Ogallala Aquifer?

14. Water Conservation Activity

15.

Predict the change in US agricultural groundwater
withdrawal from 2005-2010.
a) Irrigated land area increased, groundwater
withdrawal increased
b) Irrigated land area increased, groundwater
withdrawal decreased
c) Irrigated land area was constant, groundwater
withdrawal decreased
d) Irrigated land area was increased, groundwater
withdrawal remained constant
e) Irrigated land area decreased, groundwater
withdrawal decreased
Remember your answer. We will discuss this again later.

16.

Divide into pairs.
• Student “A” reads the original Ogallala
Aquifer Initiative document.
• Student “B” reads the Ogallala Aquifer
Initiative Progress Report.
After reading, share the main points from
each document with your neighbor.
Class “report out” activity.

17. Analyzing Data

• US groundwater withdrawals for irrigation = 49.5
billion gallons per day
• Groundwater withdrawal from Ogallala Aquifer =
19,000,000 acre feet/year (1 acre ft= 325,851 G)
• Predict the daily groundwater withdrawal from
the Ogallala Aquifer (in billions of gallons).
a) 55
b) 17
c) 5 d) 1.3 e) 0.07
52,055 acre feet per day or 16.96 billion gallons

18.

Again, predict the change in agricultural
groundwater withdrawal from 2005-2010.
a) Irrigated land area increased, groundwater
withdrawal increased
b) Irrigated land area increased, groundwater
withdrawal decreased
c) Irrigated land area was constant, groundwater
withdrawal decreased
d) Irrigated land area was increased, groundwater
withdrawal remained constant
e) Irrigated land area decreased, groundwater
withdrawal decreased
Between 2005 and 2010, there was a 6 percent decline in US
groundwater withdrawals for irrigation. However, there was a
1.5 percent increase in the US irrigated land area.

19.

On the basis of your readings:
What is responsible for the decrease in
groundwater withdrawal, even as
irrigated land area increased?

20.

What percentage of daily water withdrawn from
the Ogallala Aquifer (16.96 billion gallons/day)
would be needed to supply the city of Amarillo,
Texas (population ~200,000), with water? Amarillo
uses approximately 80 million gallons of water on a
summer day.
MUCH less than 1 percent
80/16,960,000 = 0.00000472%

21.

Could water conservation efforts in the
city of Amarillo have impacted the
decrease in groundwater withdrawals
from the Ogallala Aquifer?
Since Amarillo only uses
0.00000472 percent of the
water withdrawn from the
aquifer, it is very unlikely
that the city saving water
would have a significant
impact.