Rivers, watersheds and groundwater, and who uses the water
Grade 9 Social Studies Worksheet - Challenge Me
Circle the best answer.
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Card A. Water on land (FAO AQUASTAT). About 110,000 km³ of rain and snow falls on land each year. About 56% returns to the air from forests and natural land, about 5% from rain-fed farms, and about 39% (about 43,000 km³) becomes runoff to rivers and lakes and recharge to groundwater. Of the water people withdraw worldwide, about 69% goes to farming, 12% to towns and homes, and 19% to industry. The farming share is more than 80% in Africa and Asia and just over 20% in Europe.
About 69 percent of withdrawals go to farming. What does that figure not mean, Ari asks?
- It is a share of all water on land, so farming uses most of the 110,000 km³
- It is a share of water people withdraw, not of all the water on land
- It counts the rain on fields as well as irrigation, so it is farming’s total water use
- It is a share of runoff, so farms take about 69 percent of the 43,000 km³
The farming share is over 80 percent in Asia and just over 20 percent in Europe. Which claim do the shares support, Bo asks?
- Asia withdraws more water for farming than Europe does, since its share is higher
- The shares say nothing about farming in the two continents, since they use different totals
- Farming is a bigger share in Asia, but shares alone do not show who withdraws more
- Europe farms more land than Asia, since farming is a smaller share there
Rain-fed farms return 5 percent of the rain and snow to the air, but farming withdraws 69 percent. Why do both fit, Esme asks?
- Different bases: one is a share of rain and snow, the other of withdrawals
- Rain-fed farms use withdrawals too, so the 5 percent is part of the 69 percent
- One of the figures must be wrong, since farming cannot be both 5 and 69 percent
- Most farming relies on rain, since 5 percent is small and 69 percent is the other farms
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Card B. The Dune aquifer (made up for practice). An aquifer is a layer of rock and sand that holds water, reached by wells. The Dune aquifer holds 900 km³. Rain adds 5 km³ a year. The towns above it pump out 12 km³ a year.
The Dune aquifer holds 900 km³. A town says: “At 12 km³ a year, it lasts 75 years.” What is wrong, Jun asks?
- It lasts about 180 years, since 900 divided by the 5 km³ of rain gives 180
- Nothing: 900 divided by 12 is 75, and recharge is too small to matter
- It ignores the 5 km³ added each year: the net loss is 7, so about 129 years
- It should add the 5 km³ to the 12, so it lasts about 53 years
Towns now pump 12 km³ a year. What is the smallest pumping cut that stops the aquifer from shrinking, Kira asks?
- A cut of 5 km³ a year, so pumping falls to 7, matching the rain added
- A cut of 7 km³ a year, to 5, which matches the rain added
- A cut of 12 km³ a year, to zero, since the aquifer stops shrinking just when no one pumps
- A cut of 9 km³ a year, to 3, which leaves a margin
The aquifer is estimated to last about 129 years. Which statement about that estimate is fair, Luz asks?
- It is a forecast for the year the aquifer empties, so wells will run dry then
- It assumes pumping and rain stay as on the card; a change in either changes the date
- It is certain, since 900 divided by 7 is exact
- It tells nothing, since pumping and rain change from year to year
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Card C. The Kora River, shared by two countries (made up for practice). Altia lies upstream and Belmar downstream. Rule: Altia may take water only if at least 40 percent of the river’s natural flow still reaches the border. Natural flow, in million m³ a year: wet year 6,800; average year 4,800; dry year 3,300. Altia takes 1,800 in every year, so the border reads 5,000, 3,000 and 1,500.
In an average year, what share of the Kora’s natural flow reaches the border, Milo asks?
- About 60 percent: 3,000 of 5,000, the wet-year border reading
- About 40 percent, the cutoff the agreement sets for Belmar’s side
- About 63 percent: 3,000 of 4,800
- About 38 percent: 1,800 of 4,800, the share Altia takes
As the year gets drier, what happens to the share of natural flow that reaches the border, Noah asks?
- It rises, since less natural flow means a smaller amount to share
- It falls, from about 74 percent in a wet year to 63, then 45 in a dry year
- It falls under 40 percent in the dry year, so the agreement is broken
- It stays the same, since Altia takes the same 1,800 in each year
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Card D. The Nile (FAO AQUASTAT and general references). The White Nile begins near Lake Victoria. The Blue Nile begins near Lake Tana in Ethiopia.
Tala’s note says: “The Nile starts at one lake.” Which fix is right?
- Change it: the White Nile starts near Lake Victoria, the Blue Nile near Lake Tana
- Change it: the Blue Nile starts near Lake Victoria and the White Nile near Lake Tana
- Change it: the Nile starts where its tributaries meet, not at lakes
- Leave it: the White Nile starts at Lake Victoria, so that is the whole Nile’s start
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Card C. The Kora River, shared by two countries (made up for practice). Altia lies upstream and Belmar downstream. Rule: Altia may take water only if at least 40 percent of the river’s natural flow still reaches the border. Natural flow, in million m³ a year: wet year 6,800; average year 4,800; dry year 3,300. Altia takes 1,800 in every year, so the border reads 5,000, 3,000 and 1,500.
Zee’s note says: “The 40 percent rule gives Belmar the same amount of water every year.” Which fix is right?
- Change it: Belmar must get 1,500 in each year, the dry-year border reading
- Change it: it is a share, so the least changes: 1,320 in a dry year, 1,920 in an average
- Change it: the least is 40 percent of Altia’s 1,800, or 720, since Altia is the one taking the water
- Leave it: 40 percent of the river is a fixed amount, whatever the year