Trapped smolt due to hydro scheme.

SEDGY

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Another burning unanswered question......
My local river,Rheidol west Wales, runs for about 12 miles from the sea before the natural river has been disrupted since 1968 by a dam wall which was built in order to establish a small reservoir of about 100 aces of water. The role of this reservoir it to act as a buffer for when the hydro power station generates a large burst of water ,with this water being soaked up by the reservoir for a more controlled release down stream at the dam in to the river.
Housed within the dam their is a ‘Fish Lift’(not ladder) which consists of chambers with a mechanical operating opening and closing doors which allows the chambers water level to rise and fall and allow any fish trapped inside to leapfrog up a hight of about 10m from the river to the surface level of the reservoir and continue their migration through the reservoir and beyond back in to the natural river above .

The’Lift’ in operation ,as far as adult fish is concern , seems to be effective in both upstream and down steam migration,but there is a big unknown as to how successful the ‘Lift’ aids the down river migration of smolt , with the main problem being that the down stream inlet for the Lift being only about 3m in width located in the dam wall that extends for about 70 m.

It has been suggested that down stream migrating smolt on reaching the dam wall have three options:-

1.They could be drawn in to and through a small turbine housed in the dam wall , but I have been informed that the turbine is gated by a state of the art fish ‘ultra sound’ deflector.

2.Smolt do use the fish Lift.

3.Their are occasional when, due to high rain fall ,that the 7m high dam wall floods over and a constant water fall of water is formed which allows the smolt to literally flood over in to the river below.

My opening question is which would be the most likely choice for the smolt and why?
 

simoncassidy

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Have the salmon stock level remained or have they been decimated since the opening of the Dam? All our rivers with Hydro systems are almost dereft of any wild salmon stocks, turbines mince the smolts on their downstream migration. Two of what were once some of the best river systems for salmon in Europe the Shannon and the Erne are deviod of wild stocks. Another beautiful river the Liffey has been choked and its salmon stocks all but extinct except for a few fish who spawn in a tributary below the dams. Regardless of which of the 3 routes the smolts may take the reality is Hydro Dams block upstream and downstream migration and thus kill of migratory fish populations.
 

SEDGY

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Thank you for your reply.
A steady decline, river is more renowned for sea trout than salmon.Salmon rod catch was at its highest 125 for the season in the early 60’ ,last couple of seasons single figures.
Do the ‘ultra sound’ deflection screens not work?
 

SEDGY

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I have been told that smolt migrate by night and in the very upper layer of water .When dropping over waterfalls, they swim backwards?
So if the dam was flooding over at the ideal time of the season at night... the smolt would choose to be flooded over the dam wall?
 

SEDGY

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“Turbine mince smolt up” probably without question...but how can you prove that in order to hold them accountable for such slaughter ?
 

Ness Glen

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SEPA are focussing on smolt migration through hydros and have done some good work. You are right to be concerned about this issue. Your fish pass sounds like a Borland Lift, which can be quite effective for adults, no so sure about smolts though, although your 3m wide opening sounds generous compared to others I can think of. The location of the upstream intake is crucial in determining how well the smolts will find it though. Are the EA helpful?
 

SEDGY

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Thank you for your reply.
They dither,at best,when asked to address the subject, fog me off with some trivia excuses in the hope I will lose interest and except the situation as unchallengeable......are they hopelessly incompetent in their challenging role? YES!!!!!!!!!!!

New on the seen are ‘West Wales Rivers Trust’ who really seem to be willing to grab the bull by the horns in all fairness to them and I have been ecstatically impressed with their attitude..... thank god!
 
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