John Spilsbury
Active Member
This thread refers to the Angling Trust Document mentioned in another thread. If you have not seen it go look at the following mangled fish picture. It is on the Angling Trust News /Home page.
Most hydropower schemes are a waste of taxpayers' money and damaging to the environment, says new report - The Angling Trust
And if you have not already seen it, read the downloadable file just below the picture.
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Prompted by the picture I had a think about how Archimedes screws work.
Each "turn of the screw" holds a pocket of water. In the original usage of the screw, a handle was turned, which moved the water pockets upstream, thus lifting water from the bottom of the screw, which usually lay in the river.
However once electricity had been invented some bright spark realised that an Archimedes screw could be run backwards. The pockets of water, assisted by gravity, could be made to turn the screw and power a generator as they descended. All clever stuff. And in small scale hydro generation these pockets of water discharge into the river at an outlet channel. But such flows of water are very attractive to fish migrating upstream, salmon, seatrout, and apparently even perch. Fish though, do not tend to be engineers or scientists. They cannot see that a train of water pockets do not form a continous water-filled path upstream. They do not know that they cannot get past that first pocket. It does not stop them trying. So they remain at the lower end of the screw, where the blade is constantly turning, and unsurprisingly get sliced, as in the picture, by the edge of the rotating blade. 7 fish killed in one incident would suggest that most fish swimming into this area will be damaged or killed. Not just the odd one. So it is quite critical that the input and output channels are screened against fish entry.
Unfortunately, especially during Autumn ( when many fish run upstream) there is a deal of leaf and other debris being swept downstream. This tends to clog up such fish screens. It is not hard to see why hydro schemes will be unenthusiastic about fitting the screens. It affects their power generation and their cash subsidies from the feed-in tariffs.
It is vital that ALL micro hydro schemes are fitted with efficient fish filters of suitable mesh size, and that will work at all water levels, both at the upstream and downstream ends. The picture shows that either 1) the EA has not been insisting on screens, or 2) that particular scheme (and others?) has ignored the rules or failed to maintain the screen.
So might it be a good idea if those of you who live close to a hydro scheme go look at it and check for screens fitted below and above, and also see what mesh sizes are fitted. What size fish would be stopped by the mesh.
If for each scheme we had in here, or elsewhere, a database of sites and their screening arrangements, then maybe we might have enough evidence to present to the EA. Could I suggest that anglers initially list their results here by replying to this post.
Scheme name, River, Filter fitted upstream? Filter downstream? Mesh size?
Most hydropower schemes are a waste of taxpayers' money and damaging to the environment, says new report - The Angling Trust
And if you have not already seen it, read the downloadable file just below the picture.
_____________________________________________________________
Prompted by the picture I had a think about how Archimedes screws work.
Each "turn of the screw" holds a pocket of water. In the original usage of the screw, a handle was turned, which moved the water pockets upstream, thus lifting water from the bottom of the screw, which usually lay in the river.
However once electricity had been invented some bright spark realised that an Archimedes screw could be run backwards. The pockets of water, assisted by gravity, could be made to turn the screw and power a generator as they descended. All clever stuff. And in small scale hydro generation these pockets of water discharge into the river at an outlet channel. But such flows of water are very attractive to fish migrating upstream, salmon, seatrout, and apparently even perch. Fish though, do not tend to be engineers or scientists. They cannot see that a train of water pockets do not form a continous water-filled path upstream. They do not know that they cannot get past that first pocket. It does not stop them trying. So they remain at the lower end of the screw, where the blade is constantly turning, and unsurprisingly get sliced, as in the picture, by the edge of the rotating blade. 7 fish killed in one incident would suggest that most fish swimming into this area will be damaged or killed. Not just the odd one. So it is quite critical that the input and output channels are screened against fish entry.
Unfortunately, especially during Autumn ( when many fish run upstream) there is a deal of leaf and other debris being swept downstream. This tends to clog up such fish screens. It is not hard to see why hydro schemes will be unenthusiastic about fitting the screens. It affects their power generation and their cash subsidies from the feed-in tariffs.
It is vital that ALL micro hydro schemes are fitted with efficient fish filters of suitable mesh size, and that will work at all water levels, both at the upstream and downstream ends. The picture shows that either 1) the EA has not been insisting on screens, or 2) that particular scheme (and others?) has ignored the rules or failed to maintain the screen.
So might it be a good idea if those of you who live close to a hydro scheme go look at it and check for screens fitted below and above, and also see what mesh sizes are fitted. What size fish would be stopped by the mesh.
If for each scheme we had in here, or elsewhere, a database of sites and their screening arrangements, then maybe we might have enough evidence to present to the EA. Could I suggest that anglers initially list their results here by replying to this post.
Scheme name, River, Filter fitted upstream? Filter downstream? Mesh size?
Are the downstream screens visible? I had visions of them being below water level in the weir.
