As we get nearer and nearer to cutting the turf on the Hafod y Llan Snowdon hydro (two weeks cross fingers) we thought we’d bring some regular detailed features of the work that has gone on behind the scenes. The traditional flow splitting regime for a hydro goes like this. What is the average flow? (hands off flow) of the river and how much of the above average water can be harvested to generate energy. Habitats and species sort of dictate the percentages. the main feature which was discovered during our survey work was a little known lichen Cryptothele rhodosticta. We worked with the statutory bodies to work out a precautionary approach ie how much water do we need to leave in the river to

1. Avoid major changes to frequency or duration of drought conditions, either significantly more or less drought.
2. Maintain thin wetting films and shallow submergence.
3. Maintain high flows that scour the river bed and deter competitors

Cryptothele rhodosticta and its habitat - dilution and conductivity monitoring (chucking a fixed amount of salt into the river and monitoring the conductivity of the water further down its reach. We were able to work out how much water we had in the river) and fixed point photography to work out how much water is the right amount of water to leave

The regime was agreed after quite a bit of fixed point photography and stream flow monitoring to see how much water was needed to keep the lichen wet. Then we got on to the subjective aspects. How much water is enough to ensure the waterfall remains a dramatic feature in the landscape? The National Trust is here to conserve and share special places with people. Switching dramatic waterfalls off is not an option. What we needed to know was ‘what constitutes a frothy waterfall?’ Or how much water do we need to leave in the river to ensure that the 50,000 people who pass the waterfall still get the sense of awe and special nature of the place. In winter with high rainfall this wont be a problem. Additionally we are also ensuring that 20% more water goes over the waterfall in the main daylight hours again to maintain the spectacle.

pick a view? we opted for leaving a minimum of 225 litres per second in order to maintain the spectacle of a white waterfall. Same monitoring regime as the lichen. (salt and photography)

But in winter and high rainfall the ‘big’ white water will happen come what may. We can only take a fraction of this sort of flow (Image by Peter Bursnall – greatly missed)

If your into graphs. the 225 litres per second (on the left ) shows the cut off and where we cease generation in order to maintain the – minimum flow, lichen need and the waterfall.

The decisions and results of all of this work still means we have a viable 614kw hydro which should payback in 6 or so years but we also wanted to demonstrate that our core purpose which is to conserve can be delivered at the same time. if this hydro had taken a full on commercial attitude the payback would have been much quicker but the cost would have been much higher and I’m not taking about money but loosing something special. Can we afford such luxuries as a view with a waterfall in a world of competing needs. I don’t think we could afford not to have these fulfilling necessities to fill us with a sense of wonderment and purpose ( I will now climb down from this very tall horse)