WORKING IN A DELICATE ENVIRONMENT

ARE WATER TURBINES HARMFUL TO FISH? WE COMPARE SOME DESIGNS

Have you ever paddled a canoe or a similar small boat? If not, you have probably seen someone else doing it, either in real life or in a film or a television programme. The canoeist uses the paddle to push the water backwards and the water then automatically (i.e. following the laws of Physics) pushes the boat forwards. In other words, a form of power is created by the force of the water on the paddle.
In such a situation, the work done by the paddle is very similar to the action of the blade of an old-fashioned waterwheel - an item that used to be very common in the United Kingdom but is seen only very rarely these days. A waterwheel stands upright in flowing water, usually a river, and it looks just like a miniature version of the sort of ‘big wheel’ that we often see at fairgrounds and other popular outdoor events, but the seats that swing have been replaced by big blades (i.e. flat boards) that are fixed into position so that they provide resistance to the water that flows against them. As with the canoe, the force of the water causes the blade to move - and the wheel goes round as a result. Power is once again created by the force of the water on the blade.

It is obvious that the blades cannot move any faster than the water. Therefore, the fish etc. that are in the flow can easily pass through the wheel by swimming in the water that fills the area between any two of the blades. That short journey takes them only a very small amount of time (possibly less than one second), so they cannot come to any harm.

However, an Archimedes Screw Turbine is not as harmless to fish etc. as a waterwheel is. This type of turbine consists of a huge screw that fits exactly inside a long tube or cylinder that cannot move at all. Its action is the reverse of turning a screw to make it bore into a motionless piece of wood. The screw is itself held in position but it is made to turn by the water flowing through the cylinder. Fish etc. are at risk of receiving some slight damage if they accidentally come into contact with the outer casing as they swim in the channel of water that is formed by the thread of the screw. In addition, it can take a number of seconds for them to make that journey through the turbine.

The Hales Turbine is just like a waterwheel that has been tipped over onto its side and placed completely beneath the surface of the flowing water. Its special design allows the blades to swing freely for a few moments as the turbine turns but their front edges are well-rounded and they move very slowly, so any fish etc. can come to no harm as they pass through - a journey that takes them only about one second.

A very common type of turbine is the one that looks a bit like a ship’s propeller or a windmill. In fact, they are often called “propeller-type” turbines, and they usually have only a few blades (and sometimes only two). They are positioned completely beneath the surface in such a way that the water flows through the gaps between the blades - just as it would flow through the wheel of a bicycle if it approached one from the side. The blades are angled or twisted slightly so that they are pushed around by the water and do not simply obstruct the flow. However, they cut across the flow - so they are obviously a danger to any creatures that happen to get in the way, as their action is similar to that of a big knife coming down with great force to chop a piece of meat. For best performance, the front edges of the blades are often made sharper than those of the Hales Turbine so they can cause even greater harm to any fish with which they come into contact. That danger is obviously a very big problem when huge “propeller-type” turbines are used out in the open sea, as whales etc. can suffer some harm if the machinery is not surrounded by a form of barrier that allows the water through but keeps the creatures out.