DSE Geography | River Landforms Lesson-Prep Guide (Tutor Edition)

DSE Geography | River Landforms Lesson-Prep Guide (Tutor Edition) | Discharge, Gradient and Meanders

2026-11-01

Tutor lesson-prep guides · Secondary Geography

Students can say erosion upstream and deposition downstream but freeze when numbers appear. This lesson turns discharge into a figure they can calculate, then uses it to explain the whole long profile.

Objectives — Students can (1) calculate discharge from Q = A x v and explain the change after a tributary joins; (2) calculate gradient from drop over horizontal distance and compare course segments; (3) match erosional and depositional landforms to changes in discharge and gradient.

01 Prerequisites (3-minute check)

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

Skill	Quick check	Pass mark
Area	Area of a channel 8 m wide and 5 m deep	40 m2
Speed	Distance divided by time gives what	Average speed
Scale	On 1:25 000, what does 4 cm represent	1 km

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	River system	Catchment, source, mouth	Sketch three courses
8-22 min	Discharge	Q = A x v, tributary joins	60 m3 s-1
22-34 min	Gradient and sinuosity	Drop over distance, channel over valley length	15 m/km
34-46 min	Landform matching	V-shaped valley, waterfall, meander, floodplain, delta	Match each to a course
46-56 min	Answer format	Data, process, landform	Rewrite one paragraph
56-60 min	Exit check	Three questions marked on the spot	Work independently

03 Teaching script (read it out)

Scene 1: Discharge: one formula explains the long profile

Discharge Q is cross-sectional area times mean velocity. With 40 m2 at 1.5 m s-1, Q = 40 times 1.5 = 60 m3 s-1.
If a tributary adds 15 m3 s-1, Q rises to 75 m3 s-1 even when velocity is unchanged, because width and depth have grown.
Hydraulic radius is area over wetted perimeter, 40 over 22 = 1.82 m, and a larger value means more efficient flow.

Ask students: what is Q if velocity falls to 0.9 m s-1 (36 m3 s-1)?

Scene 2: Gradient: drop over horizontal distance

A drop of 120 m over 8 km gives 15 m per km, or 0.015, about 1.5 per cent.
Sinuosity is channel length over valley length, 12 over 8 = 1.5, and anything above 1.5 means well-developed meanders.
A steep upper course means fast flow and strong erosion, giving V-shaped valleys and waterfalls. A gentle lower course means slow flow and deposition, giving floodplains and deltas.

Reminder: gradient uses horizontal distance, not distance along the channel; using the channel overstates it.

Scene 3: Match landforms by energy, not by memory

Erosional forms such as V-shaped valleys, gorges, waterfalls and potholes belong to steep, confined upper courses where traction and saltation dominate transport.
Depositional forms such as point bars, floodplains, natural levees and deltas belong to gentle, slow lower courses. On a meander, answer the two banks separately: erosion on the concave bank, deposition on the convex bank.
A delta needs three conditions: plenty of sediment, an abrupt fall in velocity, and currents or tides too weak to remove the load.

Ask students: why is the concave bank deeper? (Faster flow erodes it while the convex bank gains sediment.)

04 Question types and worked steps

Type	Example	Steps	Answer
Calculation	Discharge	Q = A x v	60 m3 s-1
Calculation	Gradient	Drop over horizontal distance	15 m/km
Calculation	Sinuosity	Channel length over valley length	1.5
Explanation	Landform and position	Energy decides the process	Erosion upstream, deposition downstream

Sanity check (teach this): Gradient always uses horizontal distance and typically runs to tens of metres per kilometre upstream and under one downstream. Discharge only increases downstream unless evaporation or abstraction is large, so a lower discharge downstream than upstream means the units are inconsistent.

05 Independent practice (3 questions)

Question	Answer	What to watch
Discharge for 40 m2 at 1.5 m s-1	60 m3 s-1	Q = A x v
Gradient for a 120 m drop over 8 km	15 m/km	Horizontal distance, not channel length
Sinuosity for a 12 km channel in an 8 km valley	1.5	Above 1.5 means meanders

06 Common mistakes and what to say

Mistake	Student writes	Say this
Gradient from channel length	Using 12 km gives 10.0 m/km	Gradient uses horizontal distance, not how long the river is.
Mixed discharge units	Answered 60 m3 per minute	Q is per second, so the time unit must match.
Meander banks swapped	Said the convex bank erodes	The concave bank is faster and erodes; the convex bank gains sediment.
Discharge falling downstream	Said evaporation lowers discharge downstream	Tributaries add water, so discharge normally rises downstream.

07 Homework (paper, section and question numbers)

DSE Geography practice paper (rivers) — Data response and landform explanation
Secondary Geography chapter index — All chapters

08 Exit check (last 5 minutes)

Question	Answer	Decision
Discharge for 40 m2 at 1.5 m s-1	60 m3 s-1	Three correct means move on to river management
Gradient for 120 m over 8 km	15 m/km	One wrong means re-teach units
Which meander bank erodes	The concave bank	Two or more wrong means restart act one

09 Tutor FAQ

How does discharge differ from runoff?

Discharge is the volume rate through one cross-section; runoff is the water yield of the whole catchment.

Why is the lower course gentler but carries more water?

A larger catchment adds water while the relief flattens, so energy goes into transport rather than erosion.

Must a delta sit at the mouth?

Usually, but a lake inlet works too; the condition is always an abrupt fall in velocity.

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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.