However I wasn't expecting this veritable weirdness of stream, or rather burn, bifurcations at http://streetmap.co.uk/map?X=236307&Y=776062&A=Y&Z=120 The burn draining Lochan Coire nan Lochan (nice tautology) doesn't just split but each of those burns also splits! What's more the Allt Choarach Beag joins the Allt Choarach Mor and you'd think it would flow into Lochan na Coarach but no, it misses it and in fact that lochan drains from both ends!
That's got to be a couple of the strangest square kilometres around.
Better weight than wisdom, a traveller cannot carry
Good find Bob. You'd think that if a burn ever split (in the dim and distant past) at some point it would erode one channel or the other and the split would disappear. I guess the next task is to find the split on the ground!
I've actually been up that trail in Flowerdale forest. Me and two others rode up it to the loch then dragged our bikes up Baosbheinn, dragged them down the other side and picked up the trail out to Sheildaig. I seem to recall it was a complete mission....
fatbikephil wrote: ↑Sun Apr 23, 2023 5:39 pm
Good find Bob. You'd think that if a burn ever split (in the dim and distant past) at some point it would erode one channel or the other and the split would disappear. I guess the next task is to find the split on the ground!
The Arroyo Partido on the Siete Lagos route in Argentina is such a stream
One branch (on the right in this photo) flows to the Pacific Ocean and the other branch flows to the Atlantic Ocean. https://es.wikipedia.org/wiki/Arroyo_Partido
Sort of related is the capture of the Geldie Burn by the Feshie during the last 'glacial'. More intense erosion by ice further west took the water in the Geldie, which used to flow east, and it now flows west as the Feshie. It happens just near that perilous bridge on the Cairngorm Loop.
Well the bifurcations are pretty obvious on the ground. The burn splits then the two channels flow side by side for a 100m or so before properly diverging. About 50m after that the left channel splits again - I think the RH one of those rejoins the first RH channel but I didn’t follow it to be sure.
Finally the LH channel splits again. This time the main channel is the RH one but because of the very dry weather the LH was hardly flowing but it definitely heads towards the burn in the next gully.
What’s weird is that above the first split the burn is in a well defined narrow gully and it then flows over the top of a promontory as if doing a balancing act.
I’ll post a couple of pictures when I get home
Better weight than wisdom, a traveller cannot carry
This is common on deltas, where the sudden fall in water competence (velocity/discharge) causes deposition, blocking channels and causing distributaries. Does the slope angle decrease suddenly? Or is there a source of bedload from erosion or summat?
It doesn’t look deltaic in that sense. There is an easing in angle but not massive and certainly no more than you’d expect in the cross section of any slope.
There obviously has to be an underlying reason especially since it happens three times in a couple of hundred metres. For the lowest you do get the feeling of being on a broad ridge rather than in a depression but the upper two feel more like any mountain stream- I had to drop into the course and it didn’t have that feeling of being able to change course at will say during a flood event
Better weight than wisdom, a traveller cannot carry
Looking at the OS suggests a band/area of harder rock. If so, a small burn will take a very long time to erode and produce a dominant channel. Suggestions of spring line there too.
A few years ago I thought I might get interested in caving or potholing. I rapidly went off the idea but did find out about a pothole called Alum Pot. It has a stream flowing through it which pops up out of the ground again at Turn Dub.
The odd thing is that Turn Dub is on the opposite side of the river ribble so the stream flows under the ribble!
OK, here's a shot of the second bifurcation, the shot of the upper one didn't come out too well but you can see the bed of that split to the right of this shot.
The shot makes the flattening of the ground look more pronounced than it really is, in reality it's like a 5deg slope becoming a 3deg slope for a while. The slope is one of those covered in peat so there's not really any springs as such, more places where seeps become big enough to be marked as burns.
Better weight than wisdom, a traveller cannot carry
There's a river on the Continental Divide just south of Yellostone which splits with one branch heading 1353 miles to the pacific and the other3488 miles to the Atlantic.
