# Drying of the American West

## Part C: Can the River Continue to Meet Demand for Water?

1. Go to the Bureau of Reclamation's Colorado River Water Use webpage. This table is a record of the amount of water used by states and Mexico by year since record-keeping began in 1906. Scroll through the table to see if you can get a sense of how water use has changed over time.
3. Download this spreadsheet file (Excel 2007 (.xlsx) 14kB Dec18 18) of the Colorado River water use data. Open it in Microsoft Excel or a similar spreadsheet program.
4. Select appropriate columns of data and generate an X,Y (Scatter) graph to show Arizona water use by year. Repeat for the other two states and Mexico. On your graphs, add linear trend lines or 10-year moving averages to smooth the data and interpret the trends.

## Checking In

• Describe the trend of water use in the states of Arizona, California, Nevada, and the country of Mexico.
• How does water use in the states compare to the natural flow of the Colorado River (see graph in Part B) over the same time period?

## Stop and Think

9. Calculate the increase in Arizona's water consumption between the years 1914 and 2016.
10. Based on the data in this section, describe what do you think will happen if the consumption of Colorado River Water continues to grow at its present rate. Have we reached the carrying capacity of the watershed? Explain your reasoning.

### Do reservoirs prevent or merely postpone a water crisis?

1. Go to the Earth Observatory Image of the Day from August 2015, Losses in Lake Mead. Read the article and drag the slider to view before and after images of the dramatic changes in the water level of the reservoir named Lake Mead. Compare the differences between the images.

## Checking In

• In the Earth Observatory image, notice how Las Vegas in the lower left grows in size in the 15 years between images. Between 1984 and 2015, the population of Clark County, Nevada, where Las Vegas is located, nearly quadrupled from 544,893 to 2,110,330 people. What are some ways a rising population affects water levels in the reservoirs?

## Stop and Think

Imagine a half-full bathtub that is being filled by tap water at the same time as the drain is open, letting water out. Depending on the balance of water coming in and going out, the water level in the tub could get higher or lower. Compare the Lake Mead reservoir to your mental picture. Rivers flowing into the reservoir are like the tap water going into the tub and water flowing out from the dam is like water flowing down the drain.

11. 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? What would you need to know in order to predict the date of the result?
12. Based on data you examined in this lesson as well as other sources, do you think that reservoirs in arid lands prevent or merely postpone water shortages?

### Optional extension

View this graph of Historical Lake Mead water levels and describe the trends that you see.