Lab 4 Drought in SW US
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Binghamton University *
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116
Subject
Geology
Date
Dec 6, 2023
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docx
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Geol 116, Fall 2023
Name __________________
Lab 4:
Drying of the American West
Based on an exercise from the EarthLabs project, SERC, Carleton College
Part A: Reservoirs on the Colorado River
The Colorado River drains a huge area of the arid southwestern United States. While the source of much of its
water is from the high country on the western side of the Rocky Mountains, the main river flows through
desolate canyons and dry desert areas. By building dams across the river, we have been able to hold back some
of the water that would otherwise flow downstream. The result is a series of reservoirs of "saved" water that
can be tapped as it is needed. The river that carved the Grand Canyon is now responsible for providing water
for people and agriculture across the southwest.
1.
Examine the map on the next page to get familiar with the location and setting of the Colorado River
Watershed. Focus in on the locations of the large reservoirs formed by Glen Canyon Dam (Lake Powell) and
Hoover Dam (Lake Mead).
2.
The graph below shows the
water storage
(volume of water) in the two reservoirs over the last few
decades expressed in millions of acre-feet (one acre-foot is the volume of water necessary to cover an acre
to a depth of one foot). Upper line is combined storage; lower line is the storage in Lake Mead.
3.
The next two graphs show the changes in lake levels (water surface elevation) in Lake Powell (top) and Lake
Mead (bottom) over the last few years.
4.
Summarize the patterns of change in water level and total storage that you observe from the graphs.
Are
highs and lows in the reservoirs happening at the same times?
Explain.
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5.
The following graphs show water use in acre-feet per year of the Colorado River through time and the
amount of annual flow in the Colorado River.
Note that water for Mexico is the amount left over in the
Colorado River after uses in the U.S.
1906
1911
1916
1921
1926
1931
1936
1941
1946
1951
1956
1961
1966
1971
1976
1981
1986
1991
1996
2001
2006
2011
2016
0
5000000
10000000
15000000
20000000
25000000
30000000
Historical Use of Colorado River Water (acre-feet)
Arizona
California
Nevada
MEXICO
Total
Describe the trend of water use in the states of Arizona, California, Nevada, and Mexico.
How does water use in the states compare to the natural flow of the Colorado River (second and third graphs
above) over the same time period?
Given that long term changes in climate are reducing inflows into the reservoir, and that outflows through
Hoover Dam are growing to meet demand by an increasing population, what is the projected result in the
reservoir (Lake Mead)? What would you need to know in order to predict the date of the result?
Based on data you examined in this lab, do you think that reservoirs in arid lands prevent or merely postpone
water shortages?
.
Finally, review the drought situation in the western U.S.
The graph below shows the Palmer Drought Index for
the southwestern U.S. for the last 120 years.
The diagram shows a trend line. What is the trend? Do the data support the interpretation of that trend?
What does everything you’ve examined in this lab imply for near-term and future water availability for the
southwest US?
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