Guided tours from April to October

Keeping an eye on the coastline

Last month, SWACS volunteers undertook a full examination of the site and the carvings, recording any change in their condition.

Much of that work involved volunteers walking around the coastline with clipboards and cameras. But we’re also using the very latest technology to help us in the fight to keep the caves safe.

Back in 2015, as part of the digitisation project which resulted in our 4D website, the whole coastline was modelled using a technique called photogrammetry. This involved taking hundreds of overlapping aerial photographs using a drone. These were then analysed by computer to work out the lines of sight between them. The 3D coordinates of millions of points appearing in the photographs could then be calculated to give us the final 3D model.

Three years later the drone was back, flown this time by Tom Dawson of SCAPE. Photogrammetry is so accurate that the model we produced this year can be placed perfectly over the top of the earlier one and used to look very closely for any changes.

It’s most useful for monitoring the extent of coastal erosion. This is a major problem for us, and over the last 50 years a great deal of coastline has been lost due to the action of the sea. Much of the ground in front of the caves was formed of waste deposits from previous coalmining activity along this stretch of coast. Once the mining stopped, those deposits have been eaten away by the sea leaving the coastline vulnerable to storms. Recent work by Dynamic Coast shows that the coastline in front of Jonathan’s Cave has eroded by 25 metres since the 1970s.

If you carefully compare the two slides below you can see how some of the remnants of the concrete sea wall, and some of the boulders on the foreshore, have been moved around by the waves. There is also a slight encroachment in a couple of places along the coast edge.

The effect of the sea is more obvious in the images below. Here, one of the concrete gasholder bases has started to collapse further at the front and there are many boulders visible where the beach has been scoured away.

Using technology like this helps us to quickly and easily see where problems are arising, and to take what action we can to prevent damage to the caves. We hope to now take an annual drone survey as part of our monitoring and recording programme.