Land Use and Water Quality Lesson from USGS Rocky Mountain Mapping Center

Land Use and Human Impacts

Examine the USGS Map "Land Subsidence and Earth Fissures in
Alluvial Deposits in the Phoenix Area, Arizona."  This map shows
how the land has been sinking, or decreasing in elevation, in the
region.

1) Why is the land sinking in this part of Arizona?  (7 points)

2) Is this land subsidence caused by humans or a natural
occurrence?  (circle your answer) (4 points).

          human-caused        natural occurrence 

3) What is the maximum amount of land subsidence in this area? (3
points)



4) What is the average amount of subsidence over this entire
area? (3 points)


5) Do fissures, or crevasses, appear near land that is sinking or
land that is not sinking?  Circle your answer.  (3 points)

          sinking land             non-sinking land

6) Why have these fissures appeared?  (5 points)



7) Name two reasons why land subsidence is a problem (8 points):

   


8) Is land subsidence more of a problem in urban areas or rural
areas?  (3 points) Circle your answer.

          urban               rural     

Beginning in the 1940s, the federal government subsidized
development of cotton and other crops in the Arizona desert,
using groundwater and water from the Colorado River.  The
heaviest concentration of cash crops for agriculture are in the
Maricopa and Ak-Chin Indian reservations, and in the Santa Cruz
Flats.  

9) Circle the answer that best describes the climate in this
region of the USA.  (2 points)
          
     Dry-hot summer with                Wet-hot summer 
     & dry-mild winter                       & cool-wet winter


10) Based on your previous answer, would the cash crops in this
region need to be irrigated or not? (2 points)

          Yes, irrigation necessary               No irrigation
necessary


11) Are the areas covered by cash crops prone to sinking or not? 
Circle your answer.  (3 points).

          Sinking             Non-sinking

12) Explain your answer to the previous question.  (6 points)

Examine USGS Map I-857-E, "Lakes in the Colorado Springs-Castle
Rock Area, Front Range Urban Corridor, Colorado."

13) Which lake contains water with the highest pH value? (3
points)



14) Is this value at the surface basic or acidic?  Circle your
answer. (3 points)

          basic                    acidic


15) In this lake, does the water become more basic or more acidic
as one goes deeper into the lake? (3 points)



16) What are the two most significant factors that affect life in
the water of these lakes? (8 points)




17) Are most of the large lakes (with graphs on the west side of
the map) natural or human-built? (4 points)





18) How do you know? (6 points)





19) Look at the drainage patterns on the map.  Why is the quality
of water in Rampart Reservoir important to the community of
Colorado Springs? (4 points)




20) Name three reasons why the growth of algae is a problem in
these lakes. (9 points)







21) Which lake contains the most algae, and what is its
concentration? (4 points)




22) Why is the chemical and biological quality of water in these
lakes deteriorating? (7 points)