Are they waterfalls or tidal overfalls?
Since Loch Etive is the same depth on both sides of the falls and since they work in both directions, they must surely be an overfall. On the ebb tide at spring tides* the constriction is such that a vertical drop of up to 1.2 meters is created, so they do look like falls. Somehow “The Overfalls of Lora” doesn’t have quite the same feel, does it? I am going to continue to refer to them as “The Falls”.
Time lapse video
Who was Lora?
Disappointingly, there doesn’t seem to have been any such person. According to linguist David J Potts, in his book “Gaelic place names around Appin” Lora is a corruption of the Gaelic “Labhra” which he translates as “noisy”. However, other sources disagree. It has been suggested that the name Lora derives from the poems of Ossian – a purported ancient Gaelic Bard, but actually written by one James MacPherson around 1760. So it seems to be a made up name. But the ferry that operated there before the bridge was built was known as Connel Ferry and the village has the same name. Connel is an Anglicisation of “A’Choingheal” which translates as “the white dogs” referring to the white water.
The Gaelic name for the falls is A’Chraos which means voracious. If you’ve paddled a kayak through the white water on the North side, you’ll know why!
Why can’t we always see them?
Sometimes people knock on our door to ask where the Falls are and are surprised when we explain that they are right in front of them but arn’t working at the moment. There are always strong currents at the narrows, but the tidal range varies from 4.1 metres at maximum springs to only 0.5 metres at the weakest neaps, so sometimes they are raging and sometimes there is little to see. The Falls generate white water for two to five days either side of springs.
What causes the falls?
There is a ridge of rock at the narrows forming a sill more than half way across under the bridge.. The depth water over the sill at low water varies from just a few cm in places to a couple of metres. However, there is a channel about 30 metres deep near the southern bridge pier. This allows surprisingly large ships to make their way up to Bonawe Quarry. To the East of the narrows the loch is 30 km long, about 1 km wide and mostly 20 to 60 meters deep. The surface area is 28.8 square Kilometres. When the tide in the Firth of Lorn drops through its average 2.3 metre tidal range, that’s a heck of a lot of water trying to get out through such a narrow exit! Roughly 66,000,000 cubic metres in fact. And, of course, on the flood tide it is all trying to get back in again. Because of the constriction, the tidal range is much less inside the loch than it is outside. Typically, a 3 metre range at Oban produces only a 1.3 metre range at Bonawe.
How fast does the water flow?
The coastal pilot book quotes 6 knots but I have clocked 10 knots drifting through with my G.P.S. Quite powerful work boats sometimes fail to make it up against the current. The Scottish Association of Marine Science had a flow meter on the bottom for a while and recorded speeds of 12knots. I can believe it.
On a big ebb tide (after a high water of 4 metres above chart datum) the peak flow rate is about 4,600 tons PER SECOND.
Thanks to Mark Inall at SAMS for working out the numbers
Do they work both ways?
Yes. They are more spectacular on the ebb tide but the view from the bridge eastwards on the flood tide is also impressive and great fun in a sea kayak.
So how do we know when they are working? We came two hours after high water and there was nothing happening!
The short answer is to look at the dates and times page of this website. However, if you want to work it out for yourself, read on.
Because of the constriction, the water level in the loch never catches up with the level in the open sea, so there is a period when the tide is dropping in the Firth of Lorn, but still flowing inland at the narrows. Similarly, when the tide in the open sea is rising, it has to come up some way before it comes up to the level of the water still trying to get out of the loch. So the ebb tide starts 2 hours 10 minutes after high water Oban and the flood starts 2 hours fifty minutes after low water Oban. Although slack water only lasts a few minutes at high tide, it takes two and a half hours for enough height difference to be established to cause fast flows, so the falls are at their best from 4 hours 30 minutes after high water Oban until low water Oban (ebb tide) and for an hour before and thirty minutes after high water (flood tide)
Is it good for fishing?
In six years, we had only seen two small fish caught by anglers. The powerful currents make any kind of angling very difficult. There is a lot of kelp so it is good for business in the local tackle shops. However, there are always shags and other seabirds feeding. Seals and otters are also present. We have seen a seal catch a huge salmon in the falls and our local otter is sometimes seen sitting on the rocks munching fish. However, in 2010 a group of obviously expert anglers had a go and caught an impressive 9lb spur dog right in front of our house. So it seems that it is a matter of finding the right technique.
How about diving?
Divers are frequently seen drift diving the narrows. Surely this is advanced diving! Exciting/scary tales are told of fierce vertical eddies. Check out the diving items on the links page
Do you have more authoritative knowledge? If you can add any information or correct anything above, I would be delighted to hear from you.
*About spring and neap tides
Maybe I should explain a bit about the terms “spring” and “neap” which often confuse non-seagoing people. This is nothing to do with seasons of the year or Scottish vegetables. These words are derived from the old Norse words for strong and weak respectively. The tides are driven mainly by the moon but are also affected by the sun. So when the two are in line, (full moon and new moon) we get strong tides, and when they are at an angle (half moon) we get weak tides. So the tide varies from weak to strong and back in a roughly half-lunar-month cycle. If you really want to know all about it, have a look at the excellent explanation in Wikipedia