DSE Geography | Coastal Landforms and Sea-Level Rise Lesson-Prep Guide (Tutor Edition) — Wave Energy Arithmetic, Landform Reading and Coastal Management

2026-11-02

Tutor lesson-prep guides · Secondary Geography

Students can sketch a cliff and a spit yet cannot say why one bay erodes fast and the next fills up. This lesson links landforms and risk through wave energy and slope.

Objectives — Students can: (1) compute the change in wave energy from wave height and explain how refraction concentrates energy on headlands; (2) read cliffs, wave-cut platforms, spits and tombolos from slope and sediment supply, naming the process behind each; (3) compute beach retreat from a sea-level rise rate and compare hard works with soft management.

01 Prerequisites (3-minute check)

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

Skill	Quick check	Pass mark
Energy and squares	If wave height doubles, what happens to energy	It quadruples
Percentages	What share of 1.4 m is 0.264 m	About 18.9%
Slope	Horizontal distance equals rise divided by slope	Retreat = rise / slope

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-10 min	Wave energy	Energy goes with the square of height; depth sets speed	Compute a 125% rise
10-22 min	Refraction and drift	Slower waves in shallow water bend the crest	Headlands erode, bays fill
22-36 min	Landform sequence	Cliff, platform, cave, spit, tombolo	Five landforms, five processes
36-48 min	Sea-level rise	3.3 mm a year times the years, then divide by slope	26.4 cm and 13.2 m
48-56 min	Coastal management	Hard works trap sand, soft zoning retreats	State the downstream cost
56-60 min	Exit check	Three questions marked on the spot	All three right

03 Teaching script (read it out)

Scene 1: Wave energy depends on height, squared

Along one stretch of coast the normal wave is 1.2 m and a typhoon brings 1.8 m. Energy goes with the square of height: 1.8 / 1.2 = 1.5, and 1.5 squared is 2.25, so energy rises 125%. A fifty per cent rise in height more than doubles the energy, which is why a storm can strip several metres of beach in one night.
Depth sets speed: a deep-water wave in 4,000 m travels at 198.1 m/s, about 713 km/h. Entering shallow water it slows from 8.86 m/s at 8 m depth to 4.43 m/s at 2 m, the crest bends, and energy crowds onto headlands.
That is why one bay erodes while the next fills: it is geometry, not luck.

Ask students: why a storm erodes a headland more than the bay beside it (refraction focuses energy).

Scene 2: Five landforms, five processes

Reading a coast needs one routine: slope, process, landform.
Steep slope with weak rock: hydraulic action and abrasion cut a cliff, retreat leaves a wave-cut platform, compressed air widens cracks into caves, and two caves meeting make an arch.
Gentle slope with longshore drift: sediment is carried until the current slows and drops it, building a spit, and a spit reaching an island becomes a tombolo.
Drift moves 25,000 cubic metres a year; a groyne trapping sixty per cent holds 15,000 and leaves 10,000 downstream, so the beach below the groyne always erodes. Naming a landform without its process is reciting.

Ask students: why erosion gets worse below a groyne (the sediment supply is cut off).

Scene 3: Sea-level rise is division, not addition

Global mean sea level rises 3.3 mm a year, so in 80 years it is 264 mm, or 26.4 cm; against a 1.4 m tidal range that lifts the tide datum by 18.9%.
Retreat follows the Bruun rule: rise divided by slope. A beach with a slope of 0.02 retreats 13.2 m; at 0.05 it retreats only 5.28 m. The same rise moves a flat beach much further.
An 800 m long, 40 m wide, 2 m deep beach holds 64,000 cubic metres; at 1.2 m of erosion a year, 25 years takes 30 m, the whole beach.
Hard works (seawalls, groynes, sand replenishment) act fast but cost a lot and starve the coast downstream; soft management (setback zoning, wetland buffers, planning limits) is cheaper but slow and needs local consent. Strong answers combine both.

Ask students: why a flat beach retreats further than a steep cliff for the same rise (retreat equals rise divided by slope).

04 Question types and worked steps

Type	Example	Steps	Answer
Calculation	Change in wave energy	New height over old height, then square	2.25 times, +125%
Calculation	Beach retreat	Rise divided by slope	13.2 m at a slope of 0.02
Explanation	Coastal landform sequence	Slope, process, landform	Five landforms with processes
Essay	Coastal management choices	Effect, cost, downstream impact, combination	Hard plus soft

Sanity check (teach this): Energy varies with the square of height, so a fifty per cent rise in height more than doubles energy.
Sea-level rise is given in millimetres, so divide by 1,000 before using metres.
Retreat is rise divided by slope written as a decimal such as 0.02, not 2; using 2 gives an absurd 13 cm.
A groyne does not create sediment, it only redistributes it, so the downdrift beach must lose.

05 Independent practice (3 questions)

Question	Answer	What to watch
Energy change for height 1.2 m to 1.8 m	2.25 times (+125%)	Ratio 1.5 first, then square it
Retreat for 26.4 cm at a slope of 0.02	13.2 m	0.264 divided by 0.02
Sediment left downdrift after a 60% trap	10,000 cubic metres	25,000 times 0.4

06 Common mistakes and what to say

Mistake	Student writes	Say this
Treating energy as linear	Answering that a 50% rise in height gives 50% more energy	Energy is squared: 1.5 squared is 2.25.
Plugging a percentage slope	Answering a retreat of 0.0132 m	0.02 is already a decimal, so do not divide by 100 again.
Naming landforms only	Answering that this is a spit	Add longshore drift and deposition to finish the answer.
Assuming a sea wall protects the coast	Answering that a wall stops erosion	With no sediment feed the beach below erodes faster.

07 Homework (paper, section and question numbers)

Secondary geography chapter index — All chapters and practice
All lesson-prep guides — Compare other subjects

08 Exit check (last 5 minutes)

Question	Answer	Decision
Energy multiple from 1.2 m to 1.8 m	2.25 times	All three right: move to management
Retreat for 26.4 cm at 0.05	5.28 m	One wrong: reteach the division
Downdrift sediment after a 60% trap	10,000 cubic metres	Two wrong: return to act two

09 Tutor FAQ

Must students memorise every local coastal name?

No. Papers supply maps and data; the skill is inferring processes from slope and sediment supply.

Does sea-level rise always cause erosion?

A coast with a large sediment supply can keep pace; the budget and slope decide.

Are hard works always better?

They protect a short frontage quickly but cost more and worsen erosion downdrift, so answers must weigh trade-offs.

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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.