Water & Land Resources — Practice · Grade 12 Science

Chapter: Energy, Water & Material Resources

What this practice covers

By the end of Water & Land Resources you should be able to:

10 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: freshwater, watershed, aquifer, irrigation.

Problem 1

About what fraction of Earth's water is freshwater?
  1. About 97%
  2. About 3%
  3. About 30%
  4. About 50%
Answer and explanation

About 3%

Roughly 97% of Earth's water is salty ocean, leaving only about 3% as freshwater — and most of that is frozen or deep underground.

Problem 2

A watershed is best described as...
  1. a type of hydroelectric dam
  2. a machine that purifies drinking water
  3. the area of land that drains to a common body of water
  4. a large underground cave full of water
Answer and explanation

the area of land that drains to a common body of water

A watershed is all the land from which water drains into one shared river, lake, or bay.

Problem 3

For this supplied allocation model, agriculture uses about 70% of freshwater and industry about 20%, with homes and cities using the rest. What percent is used by homes and cities?
Answer and explanation

10 %

The three uses must total 100%: 100 - 70 - 20 = 10%.

Problem 4

Which is the LARGEST single use of freshwater worldwide?
  1. Bottling drinking water
  2. Household drinking and bathing
  3. Industrial cooling
  4. Agricultural irrigation
Answer and explanation

Agricultural irrigation

Agriculture, mostly through irrigation, accounts for roughly 70% of global freshwater use — far more than industry or homes.

Problem 5

Fertilizer running off farmland and down a watershed into a lake can cause...
  1. algal blooms and low-oxygen 'dead zones'
  2. cooler water temperatures
  3. an increase in drinking-water supply
  4. stronger bedrock beneath the lake
Answer and explanation

algal blooms and low-oxygen 'dead zones'

Fertilizer nutrients feed algal blooms; when the algae die and decompose they use up the oxygen, creating dead zones where fish cannot survive.

Problem 6

New York City gets much of its drinking water from the Catskill watershed and avoids building an expensive filtration plant. Explain how protecting the LAND in a watershed helps protect the WATER supply.
Answer and explanation

A watershed drains all the rain and runoff from its land into the reservoirs, so whatever happens on that land — pollution, sewage, erosion, or development — ends up in the water. By keeping the watershed forested and undeveloped, the soil and plants naturally filter and clean the water before it reaches the reservoir. Protecting the land therefore keeps the water clean without the cost of an artificial filtration plant.

Problem 7

Supply is 90 and demand 75 units/day. Find surplus in this simple account. Show the reasoning, not just the conclusion.
Hints

Efficiency improvements need to meet the full service balance.

Answer and explanation

15 units/day.

Problem 8

Why can water be abundant but still unavailable for drinking?
Hints

State what the supplied observations or conditions establish, and separate that from any assumption.

Answer and explanation

Quality, treatment, access, infrastructure and seasonal distribution can constrain usable supply.

Problem 9

Land cover changes water pathways through physical mechanismsLand cover changes water pathways through physical mechanismsLand-cover changePotential mechanismEvidence neededMore impermeable areaLess infiltration / fasterrunoffMatched rain/runoffrecordsVegetation restorationChanged interception /uptakeSoil, flow and habitatrecordsSoil compactionChanged pore connectivityInfiltration andstructure testsMechanisms depend on soil, slope, rainfall and design.
Original land-cover mechanism comparison, not a universal numerical effect size.
Interpret the supplied visual. Does a lower runoff peak always mean less total runoff volume?
Answer and explanation

No. Flow can be delayed or spread out while event volume remains similar; measure both quantities.

Infiltration is water entering soil; runoff is flow over the land surface. Impermeable cover, compaction, vegetation and drainage design can alter partitioning among infiltration, storage, evapotranspiration and rapid runoff. The effect depends on rainfall intensity, soil and slope, so a single before/after photograph is not enough to quantify it. Compare matched events or an explicit model and distinguish peak flow from total event volume.

No. Flow can be delayed or spread out while event volume remains similar; measure both quantities.

Response criteria

  • Interpret labels, structures, axes, units and directions correctly.
  • Explain the physical or environmental relationship or mechanism.
  • Respect stated assumptions and distinguish observation from inference.

Problem 10

An aquifer receives 8 million m³/year recharge, loses 2 million to streams and is pumped at 9 million. Find annual storage change and a limitation of predicting well depth from it.
Answer and explanation

Δstorage=8−2−9=−3 million m³/year. Exact water-level change also needs aquifer geometry, storage properties and spatial pumping/flow patterns.

Δstorage=8−2−9=−3 million m³/year.

Exact water-level change also needs aquifer geometry, storage properties and spatial pumping/flow patterns.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the physical or environmental mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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