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S4 Geography: River Management and Water Resources – Practice Paper 4 (Error Review, 10 Questions)
S4 Geography: River Management and Water Resources – Practice Paper 4 (Error Review, 10 Questions)
Paper four targets the usual slips: mixing gradient with discharge, litres never converted to m3, mismatched units in reservoir days, the wrong denominator for desalination cost, mm and km2 left unconverted, sinuosity treated as subtraction, and percentages subtracted as kilometres.
Quick answer All ten items are checked numerically: gradient 0.0075, discharge 60 m3/s, 1 m of sediment in 50 years, 15.6 m3 for a family of four in 30 days, 40 days of reservoir supply, desalination 33.3% dearer.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 25 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S4 Geography: River Management and Water Resources |
| Level | Error review |
02 Questions (10 items)
- FoundationA river drops from 900 m at its source to sea level over a course of 120 km. What is the average gradient as a decimal?
- FoundationA channel has a cross-sectional area of 40 m2 and the water flows at 1.5 m/s. What is the discharge?
- FoundationA floodplain receives 2 cm of sediment each year. How thick is the deposit after 50 years?
- IntermediateA family of four uses 130 L per person per day. How much water is used in 30 days, in m3?
- IntermediateA reservoir holds 24 million m3 and supplies 0.6 million m3 a day. With no inflow, for how many days can it supply water?
- IntermediateA city produces 0.8 million m3 of sewage a day and reuses 15% as reclaimed water. How much is reused and how much is discharged?
- ChallengeDesalinated water costs $12 per m3 while Dongjiang water costs $9 per m3. By what percentage is desalinated water dearer?
- ChallengeA catchment of 50 km2 receives 1 200 mm of rain a year. If all of it became runoff, what volume would that be in m3?
- ChallengeA meandering channel is 15 km long while its two ends are 5 km apart in a straight line. What is its sinuosity?
- Error redoChannelisation shortens an 8 km river by 20%. What is the new length? (Common error: 7.8 km)
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | 900 / 120 000 = 0.0075, that is 0.75%; the river falls only 0.75 m for every 100 m travelled. | Gradient is drop divided by horizontal distance, so convert kilometres to metres before dividing. |
| 2 | 40 x 1.5 = 60 m3/s. | Discharge equals cross-sectional area multiplied by velocity, giving cubic metres per second. |
| 3 | 2 x 50 = 100 cm, which is 1 m. | Multiply the yearly rate by the number of years, then convert 100 cm into 1 m. |
| 4 | 130 x 4 x 30 = 15 600 L, which is 15.6 m3. | Multiply the daily amount by people and days, then convert using 1 m3 = 1000 L. |
| 5 | 24 000 000 / 600 000 = 40 days. | Both figures are in the same unit, so divide directly without further conversion. |
| 6 | 0.8 million x 15% = 12 million m3 reused, leaving 68 million m3 discharged. | Turn the percentage into 0.15 before multiplying, then subtract to find the remainder. |
| 7 | (12 – 9) / 9 x 100% = 33.3%, about one third more expensive. | When comparing how much dearer, the cheaper Dongjiang price is the denominator, not the desalination cost. |
| 8 | 1.2 m x 50 000 000 m2 = 6 000 ten-thousand m3, that is 60 million m3 (0.06 km3). | Convert millimetres to metres and km2 to m2 (1 km2 = 1 000 000 m2) before multiplying. |
| 9 | 15 / 5 = 3, so the channel is three times the straight-line distance. | Sinuosity is a division; subtracting would only give the 10 km difference in length, not sinuosity. |
| 10 | 8 x (1 – 0.20) = 6.4 km. The answer 7.8 km treats 20% as 0.2 km; 20% of 8 km is actually 1.6 km. | A percentage must be converted into a length (8 x 20% = 1.6 km) before subtracting. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
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