As you may be aware, many anglers, following the lead of the Angling Trust, do not like water power. We have been in correspondence with them, and had a meeting in May with 5 anglers from regional and national organisations. Here is our understanding of their position - some may disagree of course, as they do not all speak with one voice. We found three main issues.
The weir pool
This is the part of the river immediately downstream of the weir.
The anglers say that the Thames, being highly developed, is a rather uniform habitat, and the only place where there is biodiversity is the weirpools, because of the water plunging over the weir. That produces a wider range of habitats, including spawning grounds, so it encourages a greater variety of fish. They believe that if we take energy out of the water we will reduce the biodiversity.
We say that there is little evidence that water plunging down a concrete spillway encourages biodiversity, it scours the river bed clean, as was shown by a detailed study at Goring. The good habitats are found a bit further downstream, where the water has slowed down. The outflow from the screws could itself provide a new and different habitat. In any case the river bed is changing continually, and it moves about, depending on the rainfall, as the water both washes away sediment and brings down more. As the habitat varies, some species gain and others lose, but the natural variation is not enough to put them at real risk. The amount of water our screws will take is less than half the average flow, so any effect they have will be negligible compared with the natural variation.
Some species migrate up and down stream while others don't go far. Going downstream is no problem, the screws move slowly and have rubber bumpers, so the fish go down through them with no damage. To go upstream they need a fish pass. There is one near the lock - the concrete channel by the very big sluice gates.
However fish going upstream swim towards the flow. If they swim toward the screws they will not find the present fish pass. New hydro schemes are required to have a new fish pass, with an outflow next to the screws so the fish can find it. Anglers say that the screws deter the fish, so their journey takes longer, and as their energy supplies are limited that reduces the chance of a successful migration. We point out that many weirs do not even have a fish pass, so installing hydro can only improve fish passage.
They also say that even if one hydro development does not hinder the fish, they could be slowed if they have to pass through many of them along the river. In our view this is speculation, with no evidence to support it, and we repeat that installing a fish pass where there was none before must improve fish passage.
Here at Abingdon we are using a newer design, that looks like a natural stream. Much of the bottom will be pebbles, to provide an extra spawning ground.
The Abbey Stream (or Mill Stream)
It flows rather slowly and is therefore seen as a good nursery for small fish. However the EA is more concerned about the part downstream of the Upper Reaches Hotel, by the car park. It is a spawning ground, so it needs water flow to stay healthy. The water comes down the spillway under the Upper Reaches. The weir in the Upper Reaches has a fixed height, which means the flow depends only on the upstream water level. The terms of the EA licence do not let us operate if the water level falls below a defined level, so the level, and therefore the flow, will remain much the same as now.
The anglers have grumbled about the Abbey Stream (some claim that we will drain it dry) but really there is not much we can do about it. It appears to be silting up very gradually, from the debris that falls into it each autumn. The EA licence also requires that we provide an extra 100m2 of pebble bed as extra spawning ground.
In our view, the claims the anglers make are speculative, with little evidence to support them. They blame the EA for charging for rod licences but not spending the money on research, and they want hydro developers to pay for more research before the EA gives them a licence. But research is very problematic. Not only are there big natural variations from year to year, there are long term effects of climate change, invasive species, pollution, changes of use, etc. With the amount of data that can realistically be collected on fish behaviour, it would be almost impossible to unravel all these effects, let alone prove that any effect, good or bad, was caused specifically by hydro developments.
We are disappointed that the Angling Trust is so negative. They issue general condemnations and urge their members to protest against any development, regardless of its merits. They want us to prove that the technology is safe for fish before we are allowed to use it. To which we could reply that they should prove that angling is safe for fish!
This is a notorious Angling Trust picture claiming that hydro blades chop up fish. When challenged they said it came from Holland, and admitted that it was not from an Archimedes screw, but could provide no other information. Can you imagine some angler standing downstream of a big hydro generator with his net, catching these fish so neatly sliced in half, and piecing them together? Mann Power Consulting with Fishtek have done trials on fish passage through Archimedes screw, showing no damage: click to see the paper.