Rising Sea levels at Woolacombe and Saunton

This is a side-hustle from my Ramson Cliff erratic post. While I was looking through the 1940 German reconnaissance photos for that, I wondered whether we could show the effect of rising sea levels on the beaches at Woolacombe and Saunton.

The result is a small interactive map: Woolacombe and Saunton at 12:44 BST, 31 August 1940.

Making it a fair comparison

To make it fair, we matched the position in the tide cycle as closely as we could with modern satellite photographs, then overlaid them. Matching the tide height alone isn't enough. On a flat beach, where the water's edge appears also depends on:

• Time after low water. The 1940 photos were taken about 90 minutes after low water.
• Rising or falling. A falling tide leaves wet sand and pools behind it, so the edge seen from the air lags the real water level. A rising tide pushes in over drier sand.
• The size of the tide. 1940 was a mid-sized tide (6.8 m range at Ilfracombe). Big spring tides move faster and push the waves further up the beach.

For example, a Sentinel-2 image from 27 September 2018 caught the sea at almost exactly the 1940 height. But the tide was falling, 100 minutes before low water, on an 8.3 m spring tide. It looks similar, but it isn't the same moment. So I kept only modern images taken on a rising tide, within 20 minutes of the 1940 timing, and with a tide range within 1.5 m of 1940's.

How the photographs were matched

The photographs were matched in the following manner:

• Time. Each German frame shows the camera's clock. It ran on German summer time (CEST), one hour ahead of British Summer Time, so the Woolacombe photos were taken at about 12:44 BST. A tide model for Ilfracombe, checked against Newlyn's real 1940 record, gives the tide at that minute.
• Tilt. The camera wasn't pointing straight down. It was tilted about 12°, from roughly 8 km up. I worked out the camera's position and tilt and laid each photo over the Environment Agency LiDAR ground heights, so that hills and cliffs fall in the right place.
• Pinning. Each photo was then pinned to thousands of features that haven't moved since 1940: roads such as Marine Drive at Woolacombe and the Saunton road, buildings, and hedge and field corners.
• Accuracy. On fixed features the 1940 photos typically sit within 2–3 m of today's imagery. Marine Drive lines up within 3 m. Among the Saunton dunes, where there is little to pin to, it is about 10 m.
• Modern images. These are Sentinel-2 and Landsat scenes from 1985 to 2023, each timed against the same tide model.

What we'd expect to see

Newlyn, the gold-standard tide gauge, shows about 20 cm of sea-level rise since 1940. On Woolacombe's gentle beach, 20 cm moves the waterline only about 8 m. On the flatter sand at Saunton the LiDAR puts it at around 20–30 m.

Conclusion

On these sorts of beaches it's invisible. Sand moving about and the natural spread of the waterline swamp it. On 1940 film, wet sand and shallow water look alike, so the 1940 edge alone can shift by up to 50 m depending on how it's read. Of 106 modern Landsat and Sentinel-2 readings, 27 match the 1940 tide. On those, the water's edge sits a median of −0.08 m from the predicted tide at Woolacombe and +0.16 m at Saunton. Neither shows a trend that stands out from the noise. The rise is real, but you measure it with a tide gauge, not on a sandy beach.

Explore the map. 1940 photos: U.S. National Archives, RG 373. Contains modified Copernicus Sentinel data. LiDAR © Environment Agency (OGL).