Clyde Weir on a dry day
I forgot I had collected some pics of the weir on the River Clyde next to Glasgow Green.
These were taken a few weeks ago, so I’m guessing that once the recent rain started – and forgot to stop – this scene looked a little different.
It took a moment for me to realise what had drawn my attention to the weir, as I’ve seen it quite regularly and almost don’t notice it at all in passing, but on this day I noticed that there was no water flowing over any of the gates. As far as I could recall, this was something I hadn’t noticed before, and more notable because there was not water running at all. I have noticed that while there may be no flow over the main gates, there’s often still a small run at the edges.
In engineering terms the weir is described as an underflow tidal sluice, having three adjustable gates, each is 80 feet long and 12 feet high.
While most rivers gradually turn from fresh to salt water as they flow towards the sea, the tidal weir on the River Clyde means that the change from fresh to salt water takes place abruptly, at the line of the weir itself.
Given the comment below, I should perhaps clarify my intended point here, which is intended to draw attention to the fact that the transition from fresh to salt cannot begin until the fresh river water passes the weir, after which it mixes with the salty sea water and gradually changes from fresh to salt as it heads for the Atlantic. Above the weir the water remains fresh, since the sea water cannot travel past the weir.
I also notice what appears to be a set of steps built into the gate on the left (the end that lies against the bank on the Glasgow Green side), usually hidden by the water running over this gate.