I have known this section of coast for about 40 years. The Highcliffe section is in Dorset and the coast is a very firm structure, not up to solid rock but still solid. The Barton on sea side where there is sumping and clear signs of collapse is much softer ground, a clay/gravel mix. The Dorset coastal protection seems to be more about creating a beach along there. Years ago all the stone groynes were not there and there was a stone beach. I seem to remember the groynes were to "catch" sand and get it to build up there, or at least to keep imported sand in place. The beach is much wider than it used to be. So I think the protection was for the beach not the cliff behind, which did not recede prior to the beach works. The WW2 listening base is still there right on the edge after 75 years.
I have known this section of coast for about 40 years. The Highcliffe section is in Dorset and the coast is a very firm structure, not up to solid rock but still solid. The Barton on sea side where there is sumping and clear signs of collapse is much softer ground, a clay/gravel mix. The Dorset coastal protection seems to be more about creating a beach along there. Years ago all the stone groynes were not there and there was a stone beach. I seem to remember the groynes were to "catch" sand and get it to build up there, or at least to keep imported sand in place. The beach is much wider than it used to be. So I think the protection was for the beach not the cliff behind, which did not recede prior to the beach works. The WW2 listening base is still there right on the edge after 75 years.