Bae Eithin, its headlands, the community council and every figure on this sheet are invented. The processes are real: boulder clay cliffs on the Welsh coast do retreat much faster than hard rock headlands, and rock armour can speed up erosion further along the coast.
1. The place
Bae Eithin is a bay about 1.6 km long on the west coast of Wales. It faces west into Cardigan Bay. The prevailing wind is from the south-west.
The bay sits between two headlands: Trwyn Du to the north and Pen yr Allt to the south. Both are made of hard sandstone. There is a sea stack 80 m off Pen yr Allt.
The cliffs in the bay are 15 to 20 m high and made of boulder clay: soft sticky clay full of stones, dumped by glaciers at the end of the last ice age. Waves undercut it and rain makes it slump.
Longshore drift moves sand and shingle along the beach from north to south.
Behind the bay are the houses of Heol y Traeth, a caravan park and the Wales Coast Path. The nearest houses stand 20 m inland of the baseline wall at T3 (see section 2).
In 2006 the county council placed 120 m of rock armour (large boulders, also called rip-rap) along the foot of the cliff at T4 to protect the caravan park. It cost £450,000.
2. How the measurements were made
A coastal officer used a GIS (Geographical Information System). She loaded four vertical aerial photographs, from 1946, 1976, 2006 and 2024, lined each one up with the modern map, and traced the cliff top on each photograph. She then drew seven transects, straight lines at right angles to the coast, and measured along each one from a fixed baseline (an old field wall built before 1900, which has not moved) to the cliff top.
A smaller distance means the cliff top is closer to the wall: the cliff has retreated.
Accuracy: the 1946 and 1976 photographs are older and less sharp, so those measurements are accurate to about ±1.5 m. The 2006 and 2024 measurements are accurate to about ±0.5 m.
3. Map A: the site map from the GIS
This map shows where the transects are. The change in the cliff top is too small to see at this scale, so the distances are given in Table 1.
The transects and the baseline wall are not drawn to scale: they are drawn longer so that you can see them. In real life the wall is between 12 m and 60 m inland of the cliff top (Table 1).
4. Table 1: distance from the baseline wall to the cliff top (metres)
Transects run from north (T1) to south (T7). The same data are in bae-eithin-cliff-retreat.csv.
Transect
Where
Rock
1946
1976
2006
2024
T1
North headland (Trwyn Du)
Sandstone
60.0
59.4
58.8
58.3
T2
South side of Trwyn Du
Sandstone
55.0
54.0
53.1
52.4
T3
North of the bay, below Heol y Traeth
Boulder clay
48.0
35.0
23.0
15.8
T4
Centre of the bay, rock armour since 2006
Boulder clay
52.0
38.5
25.0
23.8
T5
South of the rock armour
Boulder clay
50.0
37.0
24.5
12.5
T6
South of the bay
Boulder clay
45.0
33.0
21.5
12.6
T7
South headland (Pen yr Allt)
Sandstone
40.0
39.3
38.7
38.1
Useful gaps: 1946 to 2024 is 78 years. 1946 to 2006 is 60 years. 2006 to 2024 is 18 years.
5. Figure B: the infographic on the community council website
A volunteer made this infographic from the GIS data and posted it on the (invented) Bae Eithin Community Council website in March 2025. It is reproduced exactly as it was posted.
6. Comments posted under the infographic
Resident, Heol y Traeth: “Is my house going to fall in? At 0.5 m a year I make it 30-odd years. Nobody has told us anything.”
Walker: “I’m colour-blind. Which line is 1946 and which is now? They look the same to me.”
Caravan park owner: “The rock armour saved my business. And why are there no bars for T1, T2 and T7? Did they not measure them?”
Visitor: “Where do these numbers come from? How do I know they are right?”