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S4 Geography River Landforms: 10 error-correction questions with answers
S4 Geography River Landforms: 10 error-correction questions with answers
Ten classic slips: waterfall retreat direction, meander banks, a 3 per cent gradient read as 30, discharge without depth, runoff without the coefficient, a peak 4 times higher called 90 times, 9.6 per cent for a 50-year flood, fining sediment, a concave-up profile and urban peaks that are higher and quicker.
Quick answer Quick answers: 1 the direction is reversed; 2 outer erodes, inner deposits, 2 m per year; 3 three per cent; 4 45 cubic metres per second; 5 1.386 times ten to the eighth cubic metres; 6 four times, an increase of three times; 7 about 9.6 per cent; 8 finer, rounder, better sorted; 9 concave-up; 10 higher peak, shorter lag, 40 000 cubic metres more.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 questions |
| Suggested time | about 20 minutes |
| Difficulty mix | Error redo 10 |
| Chapter | Chapter: S4 Geography | River Landforms: erosion, transport, deposition and valley development |
| Level | Error correction (S4) |
02 Questions (10 items)
- Error redoA student says a waterfall retreats upstream because the river keeps pushing forward. What is wrong?
- Error redoA student reversed meanders, writing deposition on the outer bend and erosion on the inner bend. Which is correct, and what is the migration rate if a bend shifts 100 m in 50 years?
- Error redoA river falls 450 m over a horizontal distance of 15 km. A student answered a gradient of 30 per cent. What is correct?
- Error redoA river is 25 m wide and 1.2 m deep on average, flowing at 1.5 m per second. A student multiplied only width and velocity and got 37.5 cubic metres per second. What is the discharge?
- Error redoA basin of 180 square kilometres receives 2 200 mm of rain a year with a runoff coefficient of 0.35. A student answered 3.96 times ten to the eighth cubic metres. What is correct?
- Error redoPeak discharge rises from 30 to 120 cubic metres per second. A student says it increased 90 times. What is the right statement?
- Error redoWhat is the chance that a 50-year flood occurs at least once in the next five years? A student simply did 5 divided by 50 and said 10 per cent. What is correct?
- Error redoA student claims sediment gets coarser downstream because it travels further. What is the real trend?
- Error redoA student draws a river long profile as a straight declining line. What shape is correct, and why?
- Error redoA student says urbanisation lowers the flood peak and lengthens the lag time. What is correct, and how much runoff do coefficients of 0.3 and 0.7 give over 1 square kilometre with 100 mm of rain?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | The direction is reversed: the river hollows out the soft rock below and the hard rock collapses, so the fall migrates upstream. | Remember that soft rock goes first and hard rock falls later: water flows to the sea, the fall retreats to the source. |
| 2 | The outer concave bank erodes and the inner convex bank gains a point bar; the rate is 100 divided by 50, that is 2 m per year. | Centrifugal force drives water at the concave bank, which is undercut, while slower water at the convex bank deposits. |
| 3 | 3 per cent, since 450 divided by 15 000 times 100 gives 3. | The error is treating 15 km as fifteen units; gradient needs both terms in the same unit, here metres. |
| 4 | 45 cubic metres per second, because 25 times 1.2 times 1.5 equals 45. | Discharge is cross-sectional area times velocity, so omitting depth omits the whole column of water. |
| 5 | 1.386 times ten to the eighth cubic metres, from 180 million times 2.2 times 0.35. | The larger figure is all the rainfall; the coefficient is missing, and the rest infiltrates or evaporates. |
| 6 | It is 4 times the original, that is an increase of 3 times, since 120 divided by 30 is 4. | A ratio says how many times as large; an increase compares the change, so the two differ by one. |
| 7 | About 9.6 per cent, from 1 minus 0.98 to the fifth power, which is 1 minus 0.9039. | Years cannot be divided by the return period; use the complement, that no such flood happens in five years. |
| 8 | It gets finer downstream, becoming rounder and better sorted at the same time. | Velocity falls downstream, so coarse material is dropped first and only fine silt and clay travel far. |
| 9 | A concave-up curve: downstream the gradient is gentle but discharge is large, which is enough to transport the load. | Steep upper slopes move boulders; big lower discharges move fine sand, so each reach compensates differently. |
| 10 | Urbanisation raises the peak and shortens the lag; runoff rises from 30 000 to 70 000 cubic metres, 40 000 more. | Impervious surfaces and channel works deliver rain to the channel quickly while infiltration and storage fall. |
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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Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.