How people change the environment: forests, rivers, cities and pollution

Grade 9 Social Studies Worksheet

Circle the best answer.

1. Read this first

   Card C, a dam on the Nile (Aswan High Dam)

   Egypt built the dam across the Nile, 1960–1970. The dam holds back a reservoir, Lake Nasser. Effects: floods are controlled, and water is stored for irrigation over several years; falling water makes electricity, about half of Egypt's power in 1970; rich silt settles in the lake instead of reaching farms and the coast; the lake floods much of lower Nubia, and 100,000 to 120,000 people are resettled. Card D, later notes: the stored water protected Egypt's farms in the droughts of 1972–1973 and 1983–1987. By 1998 the dam made about 15% of Egypt's electricity. With less silt arriving, the coast at the Nile's mouth wears away, and some farmland has become waterlogged and salty.

2. 1.

   Which pair of effects on Cards C and D is a benefit now and a cost later, Noah asks?

   • Stored water protected farms in the 1972–1973 and 1983–1987 droughts, but less silt arriving wears the coast
   • Falling water made about half of Egypt's power in 1970, a benefit that rose to a larger share by 1998
   • Floods were controlled, which also kept rich silt arriving on the farms and the coast for decades after
   • The lake flooded lower Nubia, and the 100,000 to 120,000 people resettled later gained rich silt for their new farms
3. 2.

   The dam made about half of Egypt's electricity in 1970 and 15% in 1998. What does that show, Pia asks?

   • The dam made much less power by 1998, since its share fell from about half to about 15%, a drop of more than two thirds
   • Egypt used less electricity by 1998, since a falling share means that the total shrank as well
   • The dam's share fell, but a share can fall while output holds or rises if Egypt's total power grows
   • The dam's output fell by about 70%, since 15 is about 30% of 50 and 30% means a fall of 70%
4. 3.

   A student says the Aswan dam helps explain why the Nile's coast wears away. What do Cards C and D support, Ren asks?

   • Yes, directly: water let out of the dam wears away the coast faster than the river did before
   • No: the coast wears away from the sea, which the dam does not touch, so the dam is not part of the cause
   • Yes, through a chain: silt settles in the lake, less silt arrives at the mouth, and the coast wears away
   • Yes, if the dam traps the full silt load, since a part of it arriving would still leave the coast safe from wear
5. 4.

   Tala's note: 'The dam was good because it made half of Egypt's electricity.' Which fix fits the cards?

   • Keep it, since a source of half the power is a clear gain that the costs on the cards cannot outweigh
   • Change 'half' to '15%', since 15% is the dam's real share and half was an early figure that did not hold up for long
   • Change 'good' to 'bad', since 100,000 to 120,000 people were resettled and that outweighs any benefit
   • Say the dam made about half of Egypt's power in 1970 and 15% by 1998, and had costs such as resettlement

6. Card C, a dam on the Nile (Aswan High Dam)

   Egypt built the dam across the Nile, 1960–1970. The dam holds back a reservoir, Lake Nasser. Effects: floods are controlled, and water is stored for irrigation over several years; falling water makes electricity, about half of Egypt's power in 1970; rich silt settles in the lake instead of reaching farms and the coast; the lake floods much of lower Nubia, and 100,000 to 120,000 people are resettled. Card D, later notes: the stored water protected Egypt's farms in the droughts of 1972–1973 and 1983–1987. By 1998 the dam made about 15% of Egypt's electricity. With less silt arriving, the coast at the Nile's mouth wears away, and some farmland has become waterlogged and salty. Card E, the Kalmar River (an invented river, made up for practice): a dam finished in 1985 holds a lake about one-twentieth the size of Lake Nasser. Floods are controlled. A side river joins below the dam, so silt still reaches the farms and the coast. The coast is not wearing away, and no waterlogged or salty farmland has been reported. 4,000 people were resettled.

7. 5.

   Cards C and E differ in whether silt still reaches the coast. What does that suggest about the Nile's coast, Zee asks?

   • The Nile coast wears away because more people were resettled, so the two numbers are linked
   • The Kalmar coast is safe because its dam is smaller, so size alone explains the whole difference between the two coasts
   • Dams do not affect coasts, since the Kalmar dam was built and its coast is not wearing away
   • Where silt still reaches the coast, as on the Kalmar, it is not wearing away, which fits silt being the link
8. 6.

   The Kalmar resettled 4,000 people; the Nile dam resettled 100,000 to 120,000. Does that show the Kalmar plan was better, Ari asks?

   • Yes: the Kalmar dam was finished later, in 1985, and later plans learn from the earlier dams
   • Yes: 4,000 is far fewer than 100,000 to 120,000, so the Kalmar plan moved fewer people and so was better
   • Not by itself: the Kalmar lake is about one-twentieth the size, so fewer people lived in its flood area
   • No: both resettled people, and any resettlement makes a plan as poor as the other, whatever the number

9. Card C, a dam on the Nile (Aswan High Dam)

   Egypt built the dam across the Nile, 1960–1970. The dam holds back a reservoir, Lake Nasser. Effects: floods are controlled, and water is stored for irrigation over several years; falling water makes electricity, about half of Egypt's power in 1970; rich silt settles in the lake instead of reaching farms and the coast; the lake floods much of lower Nubia, and 100,000 to 120,000 people are resettled. Card D, later notes: the stored water protected Egypt's farms in the droughts of 1972–1973 and 1983–1987. By 1998 the dam made about 15% of Egypt's electricity. With less silt arriving, the coast at the Nile's mouth wears away, and some farmland has become waterlogged and salty.

10. 7.

    Which statement about droughts is best supported by Cards C and D, Esme asks?

    • Storage protected farms in those two periods, since no other drought took place in Egypt in that era
    • The dam ended droughts in Egypt, since farms stayed supplied through the two periods named on the card
    • The 1983–1987 drought was shorter than the 1972–1973 one, since the dam grew more useful as time went on, which the dates show
    • Water stored over several years was linked to farms staying supplied in the 1972–1973 and 1983–1987 droughts
11. 8.

    Which cost came directly from the reservoir itself, rather than from the loss of silt, Jun asks?

    • The flooding of much of lower Nubia by the lake itself, which resettled 100,000 to 120,000 people
    • Farmland turning waterlogged and salty, since the lake sits next to the farms that are watered from it
    • The coast at the Nile's mouth wearing away, since the lake holds the water that used to reach it
    • The fall in the dam's share of electricity from half to about 15%, since the lake cost more over time
12. 9.

    Kira's note: 'Silt only harms a river, so trapping it helps.' Which fix fits Card C?

    • Silt was rich and reached farms and the coast, so trapping it in the lake cost them that supply
    • Change 'silt' to 'water', since it is water that the lake keeps from reaching the farms and the coast
    • Keep it, since silt that settles in a lake leaves clearer water in the river and so helps the river
    • Change 'trapping it helps' to 'trapping it is harmless', since the silt would have gone to waste anyway

13. Card C, a dam on the Nile (Aswan High Dam)

    Egypt built the dam across the Nile, 1960–1970. The dam holds back a reservoir, Lake Nasser. Effects: floods are controlled, and water is stored for irrigation over several years; falling water makes electricity, about half of Egypt's power in 1970; rich silt settles in the lake instead of reaching farms and the coast; the lake floods much of lower Nubia, and 100,000 to 120,000 people are resettled. Card D, later notes: the stored water protected Egypt's farms in the droughts of 1972–1973 and 1983–1987. By 1998 the dam made about 15% of Egypt's electricity. With less silt arriving, the coast at the Nile's mouth wears away, and some farmland has become waterlogged and salty. Card E, the Kalmar River (an invented river, made up for practice): a dam finished in 1985 holds a lake about one-twentieth the size of Lake Nasser. Floods are controlled. A side river joins below the dam, so silt still reaches the farms and the coast. The coast is not wearing away, and no waterlogged or salty farmland has been reported. 4,000 people were resettled.

14. 10.

    The Kalmar had a side river that kept silt flowing; the Nile did not. Which question would test the silt link best, Luz asks?

    • Whether rivers with silt-trapping dams show wearing coasts and rivers where silt still arrives show none
    • Whether the Kalmar dam is newer than Lake Nasser, since a newer dam would lose less silt than older ones
    • Whether more people were resettled where the coast wears, since resettlement numbers fit the pattern
    • Whether the Nile's coast is longer than the Kalmar's, since a longer coast would wear away faster