DSE Geography - River Landforms and River Management: Lesson Prep Guide (Tutor Edition)

DSE Geography – River Landforms and River Management: Lesson Prep Guide (Tutor Edition)

2026-11-03

Tutor lesson-prep guides · Secondary Geography

Students can chant that rivers erode upstream and deposit downstream yet freeze when a cross-section or a return period appears. This lesson uses three computable numbers – discharge, hydraulic radius and sinuosity – to tie landform change to flood risk and to decide where defence money should go.

Objectives — Students can: (1) multiply a cross-section area of 20 square metres by a velocity of 1.5 metres per second to get a discharge of 30 cubic metres per second, and state how area, velocity and discharge relate; (2) divide area by wetted perimeter to get a hydraulic radius of 1.33 metres and explain why a wide shallow channel flows more slowly than a deep narrow one; (3) divide a channel length of 1200 metres by a valley length of 900 metres for a sinuosity of 1.33, convert a fifty-year flood into a 2 per cent annual chance and about a 39.7 per cent chance over twenty-five years, and then judge upstream storage, mid-basin flood relief and downstream embankments against each other.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Drainage basin	Where does river water come from?	Precipitation over the whole basin, delivered by surface and groundwater
Erosion and transport	What happens to carrying capacity as velocity rises?	It rises, and so does the largest particle size that can be moved
Cross-sections	What does the cross-sectional area mean?	The wetted area at one point, in square metres
Probability	What annual risk does a ten-year flood carry?	One in ten, or 10 per cent

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-10 min	Cross-section warm-up	Point to area and wetted perimeter on a diagram	State the difference between them
10-22 min	Discharge	20 square metres times 1.5 metres per second	30 cubic metres per second
22-32 min	Hydraulic radius	Area divided by wetted perimeter	1.33 metres
32-44 min	Sinuosity and return period	1200 over 900; a fifty-year flood	1.33; 39.7 per cent over twenty-five years
44-52 min	Question drill	One calculation, one diagram, one risk, one strategy	Eight minutes unaided
52-60 min	Exit check	Three written questions marked on the spot	Done independently

03 Teaching script (read it out)

Scene 1: Discharge is area times velocity

Discharge of 30 cubic metres per second comes from 20 square metres times 1.5 metres per second. After a storm the section may barely change while velocity rises, so discharge rises. Embanking narrows the section, and for the same discharge velocity therefore rises, which can make conditions worse downstream. Train the habit of writing units before substituting: area in square metres, velocity in metres per second, answer in cubic metres per second.

Ask the student to restate why narrowing a channel need not cut flood risk.

Scene 2: Hydraulic radius is about friction

Hydraulic radius is area divided by wetted perimeter, 20 over 15, giving 1.33 metres. A larger wetted perimeter means more contact with the bed and banks, more friction and a lower velocity, so deep narrow sections have a larger hydraulic radius and flow faster while wide shallow ones do the opposite. That is why the outer bank of a meander, deep and narrow, erodes fastest while the inner bank, shallow and wide, gains deposition. Students should link form to hydraulics instead of memorising “outer bank erodes”.

Ask the student to restate why a deep narrow section flows faster.

Scene 3: Probability, risk and the choice of works

Sinuosity is channel length over valley length, 1200 over 900, giving 1.33; above 1.5 a river counts as highly sinuous. A fifty-year flood is a 2 per cent chance each year, not one flood every fifty years: the chance of at least one in twenty-five years is one minus 0.98 to the twenty-fifth, about 39.7 per cent. Upstream afforestation and storage cut the peak, mid-basin relief channels and detention basins shave it, and downstream embankments speed the water away while pushing risk elsewhere; every option has a cost, so answers must state the trade-off rather than demand more walls. On deposition, clay particles are a tenth the size of sand yet need about 1.5 metres per second to entrain against sand at 0.2, because cohesion binds them: the least intuitive point on the Hjulstrom curve.

Ask the student to restate why clay resists erosion better than fine sand.

04 Question types and worked steps

Type	Example	Steps	Answer
Discharge	Area 20 square metres, velocity 1.5 metres per second	1) Write Q = Av 2) Substitute 3) Answer in cubic metres per second	30 cubic metres per second
Cross-section analysis	Compare flow in a deep narrow and a wide shallow section	1) Compute hydraulic radius 2) Larger perimeter means more friction 3) Conclude on velocity	Hydraulic radius 1.33 metres, the deep section is faster
Sinuosity	Channel 1200 metres, valley 900 metres	1) Divide 2) Above 1.5 is highly sinuous 3) Name outer and inner bank processes	1.33
Flood risk and strategy	A fifty-year flood over twenty-five years	1) One in fifty each year 2) 1 – (1 – p)^25 3) Compare three kinds of works	About 39.7 per cent

Sanity check (teach this): Sanity checks: discharge is in cubic metres per second, never square metres; hydraulic radius is always less than maximum depth except in a semicircular section; sinuosity is at least 1; a longer return period means a smaller annual chance but a larger cumulative risk; clay needs a higher entrainment velocity than fine sand because of cohesion, not because it is coarser; the three load percentages must total 100 (80 suspended, 15 bedload, 5 dissolved).

05 Independent practice (3 questions)

Question	Answer	What to watch
Area 20 square metres, velocity 1.5 metres per second: the discharge?	30 cubic metres per second	Check the units are written correctly
Area 20, wetted perimeter 15: the hydraulic radius?	1.33 metres	Check the student divides area by perimeter, not by depth
A fifty-year flood: the annual risk?	2 per cent	Check the student divides one by fifty

06 Common mistakes and what to say

Mistake	Student writes	Say this
Writing discharge in square metres	Discharge is 30 square metres	Discharge is a volume flow: cubic metres per second.
Judging erosion by grain size alone	The finer the particle the easier it is to wash away	Cohesion means clay needs 1.5 metres per second against sand at 0.2.
Reading a return period as a cycle	A fifty-year flood happens once every fifty years	It is a 2 per cent annual chance, about 39.7 per cent over twenty-five years.
Assuming embankments always cut risk	Raise the walls and flooding is solved	Narrowing raises velocity and shifts the peak downstream; risk moves rather than vanishes.

07 Homework (paper, section and question numbers)

Secondary Geography chapter index — Copy three keywords from the rivers chapter listed there and define each in one sentence
River management and water resources (S4 chapter) — Redo practice question 2 and give one strength and one weakness each for hard and soft engineering
Mass movement and slope safety (S4 chapter) — Use the slope data there to explain why upstream afforestation can lower a downstream peak

08 Exit check (last 5 minutes)

Question	Answer	Decision
Area 20 square metres, velocity 1.5 metres per second: the discharge?	30 cubic metres per second	A missing unit means re-teach the definition
Channel 1200 metres, valley 900 metres: the sinuosity?	1.33	An inverted division means re-teach the definition
Which resists erosion more: clay or fine sand?	Clay	Answering sand means re-teach cohesion

09 Tutor FAQ

Which year is this for?

S5 river landforms; S4 classes can start with cross-sections and discharge.

Is 60 minutes enough?

Yes; if probability is weak spend five minutes on 1 – p and set the strategy question as homework.

Is there practice attached?

The homework links to in-site chapters whose practice questions carry answers.

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A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.

Practice papers: Paper 1 (foundation: gradient, discharge and transport) | Paper 2 (advanced: catchment hydrology and sediment budget) | Paper 3 (challenge: management options and costs) | Paper 4 (error retry: unit and ratio traps)