Significance: the construction of the Churchill Barriers started in 1940 led to a fundamental change in the pattern of tidal flow around Scapa Flow. A range of coastal landforms have been created subsequently which illustrate the fundamental control of coastal configuration on the transport and deposition of sand

Churchill Barrier No 4 links the former islands of Burray and South Ronaldsay. Sand which accumulates on the narrow strip to the west of the barrier is blown over the causeway under the prevailing winds to add to an expanding dune system. During easterly blows waves will refract around either Burray Ness or Grim Ness and then approach the barrier from the east as a curved series of wave crests. This shapes the crescents of the eastern beaches, such as the Ayre of Cara.