DSE Geography — River Landforms and Catchment Management Prep Guide (for tutors) | Three courses, one discharge formula, return periods explained

2026-11-05

Tutor lesson-prep guides · Secondary Geography

Students can draw a V-shaped valley and an oxbow lake, yet answer why lowlands flood with the single word water. This lesson walks one river from source to mouth and pins every cause to discharge, gradient or return period.

Objectives — Students can: (1) name the dominant process and one landform in each course; (2) convert a 120 square kilometre catchment and 2400 mm of rain into about 1.30 hundred million cubic metres of runoff; (3) explain a 50-year return period as a 2 percent annual chance and weigh three defence strategies.

01 Prerequisites (3-minute check)

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

Skill	Quick check	Pass mark
Water cycle	Where does rain that lands on the ground end up?	Evaporation, infiltration and surface runoff
Erosion	As velocity rises, does the largest transported particle grow or shrink?	It grows, so uplands carry boulders and lowlands carry silt
Units	How many square metres are in one square kilometre?	One million

02 Lesson flow (45 minutes)

Time	Stage	Tutor does	Student does
0-5 min	Prior knowledge check	Ask the three prior questions and write erosion, transport, deposition on the board	Answer orally and copy any wrong item once
5-17 min	Act one: three courses	Draw the river from ridge to sea, labelling process and landform	Copy the three courses and add one landform each
17-30 min	Act two: runoff and discharge	Show how 120 km2 and 2400 mm give hundreds of millions of cubic metres	Compute once, then compute discharge
30-40 min	Act three: floods and defence	Use the 50-year event to teach probability, then compare three schemes	Compute the 30-year chance
40-43 min	One-sentence summary	Ask for one sentence on why lowlands flood worse	Answer orally; tutor corrects only causal wording
43-45 min	Exit check	Hand out three items and collect them	Work alone with books closed

03 Teaching script (read it out)

Scene 1: Act one: one river, three jobs

Upper course: steep, fast, vertical erosion dominates, giving V-shaped valleys, waterfalls and gorges.
Middle course: gradient eases, lateral erosion and transport share the work, giving meanders and floodplains.
Lower course: flattest, energy falls short, deposition dominates, giving deltas and levees.
One memory line: cut, bend, build. Every landform question starts by asking which course it belongs to.

Ask students to repeat: cut, bend, build, three courses with three jobs.

Scene 2: Act two: discharge is three numbers multiplied

Annual runoff equals catchment area times rainfall times runoff coefficient. 120 km2 is 120 million m2, times 2.4 m of rain gives 2.88 hundred million m3, times 0.45 gives 1.296.
Discharge equals width times mean depth times velocity: 12 m by 1.5 m by 1.6 m per second, which is 28.8 cubic metres per second, or about 249 ten-thousand m3 a day.
The commonest error is treating millimetres as metres, which inflates the answer a thousandfold.

Ask students to repeat: area times rain times coefficient is runoff; width times depth times velocity is discharge.

Scene 3: Act three: a return period is a probability

A 50-year flood does not arrive once every 50 years; each year carries a 2 percent chance of being exceeded.
Meeting it at least once in thirty years is one minus 0.98 to the thirtieth power, about 45.5 percent, close to a coin flip.
Each strategy has a price: afforestation and storage basins are cheap but need land; higher embankments act fast but fail catastrophically; banning floodplain development works best and offends most.
Any judgement answer must state the trade-off, not just name a scheme.

Ask students to repeat: the return period is an annual chance, and thirty years is close to even odds.

04 Question types and worked steps

Type	Example	Steps	Answer
Identify the landform	A V-shaped cross-section with boulders on the bed	Read shape and calibre, infer vertical erosion, place in the upper course	Upper course, V-shaped valley, erosion
Runoff calculation	Catchment 120 km2, rainfall 2400 mm, coefficient 0.45	Area times rain times coefficient, converted to hundred million m3	1.296 hundred million m3
Discharge calculation	Width 12 m, depth 1.5 m, velocity 1.6 m per second	Multiply the three	28.8 cubic metres per second
Defence comparison	Afforestation, higher embankments or limiting development	Three columns: cost, speed, consequence of failure	One sentence each, then a stated trade-off

Sanity check (teach this): Three read-backs: (1) divide millimetres by a thousand before multiplying, or runoff is ten thousand times too large; (2) width times depth times velocity gives cubic metres per second, not square metres; (3) a drop of 300 m over 60 km is 5 m per kilometre, so hundreds of metres per kilometre means the division slipped.

05 Independent practice (3 questions)

Question	Answer	What to watch
Catchment 60 km2, rainfall 2000 mm, coefficient 0.4. Find annual runoff.	48 million cubic metres	Check the millimetre conversion and the coefficient
Width 20 m, depth 2 m, velocity 1 m per second. Find discharge.	40 cubic metres per second	Check whether a term was dropped
A ten-year flood: chance of meeting it within three years?	About 27.1 percent	Check one minus 0.9 cubed rather than a flat 30 percent

06 Common mistakes and what to say

Mistake	Student writes	Say this
Millimetres treated as metres	120 times 2400 gives 2.88 billion cubic metres	2400 mm is 2.4 m, so divide by a thousand.
Return period treated as a cycle	A fifty-year flood happens once in fifty years	It is a 2 percent annual chance and can strike twice in a row.
Lowland flooding blamed on volume alone	The lowlands flood because there is more water	Name the flat gradient, falling competence, raised bed and stacked peaks.
Process matched to the wrong course	Meanders are cut by upper-course erosion	Meanders come from lateral erosion and deposition in the middle course.

07 Homework (paper, section and question numbers)

Redo this chapter — Redo the three items, writing the formula before substituting
Plate tectonics — Compare warning times for river floods and earthquakes in three points
Geography chapter index — Pick one more chapter and draw the cross-section only

08 Exit check (last 5 minutes)

Question	Answer	Decision
Catchment 120 km2, rain 2400 mm, coefficient 0.45: runoff?	1.30 hundred million m3	Error: skipping the millimetre conversion
Annual exceedance chance of a 50-year flood?	2 percent	Error: answering once every {RP_YR} years
Which course and process build a delta?	Lower course, deposition	Error: answering middle course or erosion

09 Tutor FAQ

Which year is this for?

Mainly S4, and useful as a summary when S5 revisits rivers.

Is 45 minutes enough for three courses and two formulas?

Yes, because only one river is computed in full and students repeat it with new numbers.

Is there a companion worksheet?

Three practice items with answers on the page, plus the plate tectonics chapter.

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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.