Churchill barriers

This is the view from the Orkney mainland looking at Churchill barrier number one. This causeway allows drivers to travel over to the island of Lamb Holm.

[edit] Introduction

The Churchill barriers were four solid causeways in Orkney constructed during the Second World War. The barriers were used as a defensive measure to prevent enemy ships and submarines from entering Scapa Flow, which housed the bulk of Britain’s fleet at the time.

The move was ordered by Prime Minister Winston Churchill in response to the sinking of the HMS Royal Oak in Scapa Bay in October 1939. The attack by a German submarine - which had been able to evade the ineffective submarine defences in place at the time - killed 835 soldiers.

[edit] Construction

The scheme to build the barriers was designed and supervised by Sir Arthur Whitaker, Civil Engineer-in-Chief of the Admiralty. The contractors were Balfour Beatty & Co Ltd. Italian prisoners of war who were interned at Lamb Holm formed part of the workforce that made the concrete blocks and built the structure.

Building long fixed barriers across bodies of tidal water presented unusual engineering requirements in the mid-20th century. In this period, solid causeways were not a normal response to civilian transport needs, with bridges or ferries usually preferred when open water had to be crossed. The barriers’ designers had to take account of the fast flowing tidal water in narrow, but relatively deep channels. The barriers were designed to withstand a 4-5 knot tidal current.

The barriers were ingenious in their construction. Built using bolsters, these wire cages or baskets were filled with broken rock and then dropped into the water of the channel.

Most of this deep structure is underwater. A road carriageway formed from dumped aggregate and horizontally laid concrete blocks overlies the causeway base. In total, all four barriers required about 250,000 tons of stone rubble and 66,000 concrete blocks.

[edit] Protected status

The barriers provide a vital road link from the Orkney mainland to South Ronaldsay.

In November 2016, two of the four barriers were listed at Category A - the highest status - by Historic Environment Scotland. This means that they are recognised as being of national or international importance. Only around 8% of Scotland’s 47,000 listed buildings are recognised in this category.

The two listed structures are Churchill barrier number three (which links Glimps Holm and Burray and number four (which links Burray and South Ronaldsay). Historic Environment Scotland did not consider it appropriate to list barriers one and two due to proposed bridge developments because of structural integrity issues caused by rising sea levels.

Despite their significance and protected status, the barriers face flood risk and require preservation.

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