Monday 26 May 2014

Furnishing four further facts
A while back, through a blogpost and its comments, I&T surmised upon the origins of the sand that has appeared adjacent to Churchill Barrier 4 in the intervening years since the barrier's construction.

More recently, a letter in The Orcadian newspaper held a clue to solve the mystery.

The letter writer, Morris Pottinger (who I understand once lived on Orkney, but now resides on the other side of the Pentland Firth in Caithness), was discussing a problem associated with the ferry port of Burwick  in South Ronaldsay.

The paragraphs that particularly caught my eye were:

"I studied old pre-war tidal charts and new post-war ones, and was struck by the difference from pre-Churchill Barriers and afterwards in relation to the Lothar Rock outside Burwick.

Pre-war, the tides did indeed hasten on flood or ebb past the Lothar, but after 1945 the flow increased massively at that point on the south-east corner of South Ronaldsay.

The effect of this changed, and increased, flow on Caithness is that no longer does shell sand come in at John o' Groats, Duncansby or the other shell sand beaches we had.

A look at the east side of the Barrier between Burray and South Ronaldsay tells you where it now lodges. Not too far to find a reason.

The four channels now Barriered no longer allow ebb and flow to pass through, channelling all the  tides either direction past the Lothar..."

In the above map (pre-barriers!), Burray can be seen top right, Burwick is on the south-west corner of South Ronaldsay and Duncansby Head is shown in the north-east corner of Caithness, on the Scottish mainland.


Martin said...

A case of joining the dots. Clever. And yes, so the Pentland firth flows stronger because all the water has to pass one side or other of Orkney, rather than through Scapa flow and the barriers as it used to do. Interesting that the difference is so marked though.

Imperfect and Tense said...

It certainly sounds plausible to me. But unless bridges or tunnels are built to replace the barriers, we'll not have the opportunity to see if the reverse is true.