AP Environmental Science 1.7: Hydrologic Cycle

Practice AP Environmental Science questions on water reservoirs, phase changes, watersheds, flow, percentages, and unit conversions.

[Maximum number: 6]

The Rocky Mountains, the headwaters for the Colorado River, have experienced a severe drought for many of the past twenty years. States and cities downstream that depend on the river water have had to find solutions to the reduced water flow.
One city located downstream from the Rocky Mountains is Las Vegas, Nevada. In Las Vegas, one solution to reduce the amount of water used for irrigation is to remove landscaping and lawns that use grasses not native to the local area and replace them with desert-tolerant landscaping.

(a)

Calculate the number of million acre-feet (maf) of water currently in Lake Powell. Show your work.

In 2021, after years of drought, Lake Powell held 7.9 million acre-feet (maf) of water. One million acre-feet is equivalent to $3.26 \times 10^{11}$ gallons.

[ 2 ]

Calculate the number of million acre-feet (maf) of water currently in Lake Powell. Show your work.

One point for the correct setup to calculate number of million acre-feet (maf) of water currently in the lake:

Accept one of the following:

- 25.16 maf $\times 36 \%$

- 25.16 × 0.36

1 point

One point for the correct calculation of the number of million acre-feet (maf) of water currently in the lake:

Accept one of the following:

- 9.0576

- 9.058

- 9.06

- 9.1

1 point

Total for part (e)

2 points

(b)

The watershed of the Upper Colorado River contributes an average of 9.60 maf of water to Lake Powell annually. The melted mountain snow found in the watershed contributes 50\% of the average river flow into Lake Powell. In 2021, the river flow was 36% of the annual average. Assuming that all resources to that flow contributed the same proportions as in prior years, calculate the amount of water (in million acre-feet) that was contributed by the melted mountain snow in 2021. Show your work.

[ 2 ]

One point for the correct setup to calculate amount of water in million acre-feet that was contributed by the melted mountain snow:

Accept one of the following:

- 9.60 maf $\times 36 \% \times 50 \%$

- 9.60 maf × 0.36 × 0.5

- $9.60 \times 0.36 \times 0.5$

1 point

One point for the correct calculation of the amount of water in million acre-feet:

Accept one of the following:

- 1.728

- 1.73

- 1.7

1 point

Total for part (f)

2 points

(c)

The average household in the United States consumes $5.0 \times 10^{4}$ gallons of water in a year. Calculate the number of households that could be supported for one year by the average flow of 9.60 maf of water into Lake Powell. Show your work.

[ 2 ]

The average household in the United States consumes $5.0 \times 10^{4}$ gallons of water in a year. Calculate the number of households that could be supported for one year by the average flow of 9.60 maf of water into Lake Powell. Show your work.
One point for the correct setup to calculate the number of households that could be supported for one year by the average watershed flow:
Accept one of the following:

- 9.60 maf $\times \frac{3.26 \times 10^{11} \text { gallons }}{1 \text { maf }} \times \frac{1 \text { household }}{5.0 \times 10^{4} \text { gallons }}$

- 9.60 maf $\times \frac{3.26 \times 10^{11} \text { gallons }}{5.0 \times 10^{4} \text { gallons }}$

- $9.60 \times \frac{3.26 \times 10^{11}}{5.0 \times 10^{4}}$

One point for the correct calculation of the number of households:
1 point
Accept one of the following:

- 62,592,000

- $6.2592 \times 10^{7}$

Total for part (g)

for question 3

10 points

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Covered syllabus points

1.7 The Hydrologic (Water) Cycle question 1

Question (a)

Question (b)

Question (c)