Why is the load finer downstream?

Fine particles settle slowly and travel farther, while coarse gravel is dropped in the upper course.

Why does urbanisation raise flood peaks?

Hard surfaces stop infiltration, so a large volume of water reaches the river in a short time.

S5 Geography Rivers, Paper 1: gradient, discharge and erosion

2026-11-02

Paper 1 works from gradient and channel discharge to V-shaped valleys, meander bends, the three erosion processes and downstream sorting, then uses runoff coefficients for flood peaks.

Focus　Gradient is fall over length, discharge is cross section times velocity, the outer bend erodes and the inner bend deposits, and hard surfaces raise the runoff coefficient.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S5 Geography: Rivers
Level	S5

02　Questions (10 items)

FoundationA river runs 120 km with a fall of 900 m. What is its average gradient in metres per kilometre?
FoundationWhich process mainly forms V-shaped valleys in the upper course?
FoundationWhat dominates at the outer and inner bends of a meander?
FoundationName the three main ways a river erodes its bed.
IntermediateA channel is 20 m wide and 2.5 m deep with a flow of 1.2 m per second. What is the discharge?
IntermediateA catchment of 50 square kilometres receives 80 mm of rain that all becomes runoff. What is the runoff volume?
IntermediateIf velocity doubles, roughly how many times larger are the particles a river can carry?
ChallengeHow does bed load size change from the upper to the lower course?
ChallengeUrbanisation raises the runoff coefficient from 0.3 to 0.7. With the same 100 mm of rain, by what factor does runoff rise?
Error redoError: a student says the inner bend of a meander has the fastest flow and most erosion. What is correct?

03　Answers and one-line notes

#	Answer	One-line note
1	7.5 m per km	Gradient is fall divided by length, and 900 divided by 120 is 7.5.
2	Vertical erosion, cutting a deep narrow valley	A steep upper course gives fast flow, so the river cuts down into the rock and leaves a narrow V-shaped valley.
3	Erosion at the fast outer bend and deposition at the slow inner bend	Water runs faster round the outer bend and erodes the bank, while the slow inner bend drops its load as a bar.
4	Hydraulic action, abrasion and solution	Water pressure lifts loose material, the load grinds the bed, and soluble rock such as limestone is dissolved.
5	60 cubic metres per second	Discharge is cross section times velocity, so 20 times 2.5 is 50 and times 1.2 is 60.
6	4 000 000 cubic metres	Fifty square kilometres is fifty million square metres, and times 0.08 m gives four million cubic metres.
7	About four times, since competence rises with the square of velocity	Textbooks take competence as proportional to velocity squared, so doubling speed quadruples the particle size.
8	Boulders, sand, silt then clay, from largest to smallest	Boulders are dropped first because water cannot move them far, so the finest clay travels farthest.
9	About 2.33 times, from 30 mm to 70 mm	Point three times 100 is 30 mm and point seven times 100 is 70 mm, and 70 over 30 is 2.33.
10	The outer bend is fastest and erodes most, while the inner bend is slower and depositional	Centrifugal force pushes water to the outside of the bend, so that bank is scoured while a point bar builds inside.

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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