Improving a coastal erosion infographic: Bae Eithin

Transect	Rock	Retreat 1946 to 2024 (m)	Rate (m per year)
T1	Sandstone	60.0 − 58.3 = 1.7	1.7 ÷ 78 = 0.02
T2	Sandstone	55.0 − 52.4 = 2.6	2.6 ÷ 78 = 0.03
T3	Boulder clay	48.0 − 15.8 = 32.2	32.2 ÷ 78 = 0.41
T4	Boulder clay	52.0 − 23.8 = 28.2	28.2 ÷ 78 = 0.36
T5	Boulder clay	50.0 − 12.5 = 37.5	37.5 ÷ 78 = 0.48
T6	Boulder clay	45.0 − 12.6 = 32.4	32.4 ÷ 78 = 0.42
T7	Sandstone	40.0 − 38.1 = 1.9	1.9 ÷ 78 = 0.02

(a) Headlands: (1.7 + 2.6 + 1.9) ÷ 3 = 2.07 m, and 2.07 ÷ 78 = 0.03 m per year. Bay: (32.2 + 28.2 + 37.5 + 32.4) ÷ 4 = 32.6 m, and 32.6 ÷ 78 = 0.42 m per year. All seven: 136.5 ÷ 7 = 19.5 m, and 19.5 ÷ 78 = 0.25 m per year.

(b) The coast retreats in a clear pattern. The two headlands barely move: T1, T2 and T7 have all retreated less than 3 m in 78 years, about 0.02 to 0.03 m a year. The bay in between retreats about 15 times faster, 0.42 m a year on average, and T5 is the fastest at 0.48 m a year. This is because Bae Eithin is a discordant coast: the headlands are hard sandstone, which is resistant to hydraulic action and abrasion, while the bay is soft boulder clay. Waves undercut the clay, and rain soaks into it so that it slumps, a form of mass movement. So the rock type controls the rate.

Transect	Rate 1946 to 2006	Rate 2006 to 2024
T4 (rock armour)	27.0 ÷ 60 = 0.45	1.2 ÷ 18 = 0.07
T5 (just south)	25.5 ÷ 60 = 0.43	12.0 ÷ 18 = 0.67

The claim is only half true. At T4 the rock armour worked: the rate fell from 0.45 to 0.07 m a year, a cut of about 85%, because the boulders absorb the wave energy before it reaches the cliff foot. But just south of it, at T5, the rate rose from 0.43 to 0.67 m a year, about 57% faster. Longshore drift moves material from north to south. The armour stops the clay at T4 eroding, so less sand and shingle is supplied to the beach further south. A thinner beach at T5 absorbs less wave energy, so more reaches the cliff. Waves also bend round the end of the armour and attack the unprotected cliff next to it. So the armour protected the caravan park but moved part of the problem south.

	Fault	Why it matters to a resident	How to fix it
1	The headline says the cliffs retreat 0.5 m every year. The real mean is 0.25 m; the bay is 0.42 m and the headlands 0.03 m.	It doubles the average and frightens people. The resident on Heol y Traeth has used it to work out a false date for losing his house.	“The clay cliffs in the bay are retreating at about 0.4 m a year. The sandstone headlands have hardly moved.”
2	The bar chart axis starts at 20, not 0.	T1, T2 and T7 have no bars, so it looks as if they were not measured (the caravan owner’s comment). T5 looks more than twice T4, when it is only 1.3 times.	Start the axis at 0 so every bar’s height is in proportion.
3	The bars are sorted by size, not from north to south.	Readers cannot see the pattern of headland, bay, headland, or find the transect near their own home.	Put the bars in order T1 to T7 and shade the sandstone bars differently from the clay bars.
4	The map has two lines, red and green, with no key, no scale and no north arrow.	Nobody can tell which line is 1946 and which is 2024, and a colour-blind reader cannot tell them apart at all (the walker’s comment).	Add a key, a scale bar and a north arrow. Use a dashed line for 1946 and a solid line for 2024, in blue and orange.
5	There is no source, date or accuracy statement, and the rock armour line is one-sided.	Readers cannot check the figures (the visitor’s comment), and the caravan owner is told the armour failed when it protected his site.	Add a source line, and one balanced sentence: the armour slowed T4 but T5 speeded up.

A pupil’s sketch would include these elements. This version is drawn to show what “secure” looks like.

Beside the chart, a small map shows the seven transects with a key (dashed blue line: cliff top 1946; solid orange line: cliff top 2024), a north arrow and a scale bar.

Choice 1: bars in order T1 to T7, shaded by rock type. Residents can find the transect nearest their home, and the shading shows at a glance that the clay retreats and the sandstone does not. Disadvantage: the chart does not show when the retreat happened, so a resident cannot see that T5 has speeded up since 2006.

Choice 2: a calm headline with the real figure. The purpose is to inform residents, not to alarm them, and the figure is one they can check. Disadvantage: a calm headline may get fewer people to read it, and people who skim may miss that some houses behind T3 are still at long-term risk.