Meno-wier-ed!!

NB: YAM is away travelling (again!) for a week so please continue to leave your comments so that when she returns she knows she has not been forgotten...

"Help me out here. I'm only recently introduced to weirs. I encountered them in old stories and deduced they were a blocking of a waterway, but to trap fish.
Recently I decided they were just dams. Nothing folkway magical at all.
But you just said "trap side." Does that simply mean where the water is trapped? And the one in the picture is new to me. Are the slits just another sort of escapement to keep the level behind?"


One of my delightful blogpals and commenters, Joanne, asked a very excellent question on Friday's post, as you see above.  It prompted today's entry.

I grew up close to 'burns', streams, creeks, rivers... and almost every one had a weir of some description upon it.  If it didn't, then we built one!  In the borders of Scotland, near my grandparents old home, there was a peat burn - simply a small stream close to its spring source. When it runs through peatland, it takes on a particular look and taste - oh yes we would drink it, irrespective of where the sheep were...

The point of this post though is to clarify for Joanne and anyone else, the purpose of a weir.  Well, quite simply it is a way to control water flow such that -
a) a pool or pools can be formed from which to obtain domestic water supply
b) management in the case of flooding, erosion and/or fishing stocks
c) often used where watermills are built 
d) in the case of children on small burns, to watch how the trout leap over it.  

That last is not official of course; purely experimental.  Sometimes beneficial for tea.

There are many types and sizes of weir, but the key difference between these and dams is that water can still flow freely; they are merely an extension of a natural phenomenon seen at water falls and the like which Man has adapted to his own purposes.  Nowadays they can serve as important points for research.  If memory serves, it can alter the ecology along the banks and (I think) the oxygen/nitrogen levels.  

[...It occurs to me that one might have done a search on this, but don't want this sounding too much like a scientific article, so am only relating what I remember from school and father's education!]

The Edgeworth David Park weir which prompted the query was built to control flooding. So, yes Joanne, my reference to 'trap' meant the water itself.  It also, as you saw, traps debris.  The grating style allows for seepage of the water, even if there is major build up of rubbish, so that the problem averted doesn't then take place behind it!!  The  banks are deep, but even I could see that the previous day's storm had caused the creek to rise almost to the top.  How?  By the lie of the vegetation, particularly the rock orchids, as well as the erosion that had taken place at one part of the bank.  So here are a series of piccies I hope will demonstrate;


copyright Yamini Ali MacLean


Here from my first visit to the park you see one of the ducklings atop the grating weir.  I didn't get a full frame but trust me when I say the water level behind it at this time was little more than 12 to 15 inches.  The weir is about one metre high.






copyright Yamini Ali MacLean




This telephoto shot of the ducklings down the banking near the bridge gives no idea of the steepness or the depth down to that water, which is trickling over its sandstone base at about 6 to 8 inches depth.  Take note of the lay of the land...
copyright Yamini Ali MacLean






...the bit of soil preserver net they are standing on is the bit you can see bottom mid-right in this next shot, post-storm.  The force of flow has lifted the net higher up the bank and scoured away all the earth which had held grasses and ferns.  The larger rock in the water you see bottom right and also the one which looks like it is next to the netting, were not visible before this!! The drop from the netting to that rock is actually around two feet. The width of the creek has increased by about half a metre at this point and in this particular shot, although the ebb has reduced a lot, it is still about another six inches deeper than usual - but clear enough to see all the way to the bottom.

Had that water not been held back by the weir, it would certainly have banked up over the road just up from the blockade.

Does that help?  &*>


5 comments:

  1. Not sure what you are saying here all I know was as a kid I went swimming at the weir at Ingleburn not sure if it's still there.
    Merle..........

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  2. I had to do a little bit of research because the word weir in my mind seemed to be associated with fish ladders, which are very common in British Columbia where I spent most of my life. The rivers run sharply downhill in many cases, BC being so mountainous, so dams and weirs are almost always accompanied by fish ladders.
    Love these photos!
    K

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  3. That is wonderful information. I had heard the term and have even seen a few weirs but all I knew was they were smaller than dams and sometimes used to alter the water flow. I really enjoyed reading this.

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  4. I too grew up around weirs, and it never occurred to me that they would be unfamiliar to some folk. One of the pleasures of blogging - discovering in fine detail the different perspectives of our readers.
    Hope all's going/went well on Bute. Did you visit the fancy Victorian toilets in Rothesay???
    Cheers,
    Gail.

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  5. Since most of the country I hail from is flat, I don't really think we have that many. But I love reading about what it actually is, since I had heard the term, but never knew what it was (I just thought you didn't know how to spell weird!)

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