Groundwater Resources: The Desert Southwest

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

What sources other than agriculture could be contributing to the decline in groundwater?

How do these sources use groundwater?

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.

Agriculture• Using the maps below, which regions of the United States

would be best for growing crops?

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

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.

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?

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.

Groundwater Depletion• Where is the Ogallala Aquifer on these maps? Describe the

trends around this aquifer.

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?

What negative impacts might these groups be concerned about?

• 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.

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?

Water Conservation Activity

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 decreasedRemember your answer. We will discuss this again later.

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.

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

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 decreasedBetween 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.

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

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.

80/16,960,000 = 0.00000472%MUCH less than 1 percent

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.