Wheel proposal requires a lot more careful thought

While I am happy to support realistic proposals to use local watercourses to generate renewable energy, I am writing to point out that there are some important considerations regarding the plans to revive a water wheel near the site of Waterside Mill which seem to have been omitted, or gone unreported.

I am not clear whether the aim of the Todmorden Civic Society is to construct something which is to represent the importance of water power in the industrial development of Todmorden, or a working example of it. If the former, then putting a piece of sculpture beside the river should not present any impossible problem. If the latter, then putting a water wheel in the middle of a £13 million pound flood alleviation scheme could cause a lot of problems.

The biggest problem with Mr Caldwell’s drawing of a proposed wheel, illustrated in the Tod News (May 24 and June 14) is that it runs contrary to long established practice for water mills. Putting a water wheel across and above the river would make it impossible to use the river as a source of water power. Even placing a non-working model or sculpture in that position would, unfortunately, only serve to illustrate how little we understand the history of water power on the river.

Any new water wheel would have to lie parallel to the river, take its water from the river and feed it back in, none of which are possible on the arrangement shown in the illustration.

One of the main points to be considered is that a water wheel does not operate in isolation, but is the focal point of system of water management. In the case of Todmorden this system used to be very extensive and complicated, linking mills and factories on the same river or stream, each with its own mill lodge.

The old mill lodges, many of which have been built on or destroyed, were a crucial part of managing the water so that it could be used at a high rate during the working day, but stored in the lodges during the whole 24 hours of the day. As the area of Shade Primary School was one of the lodges supplying Waterside, I can’t think that the present governors would be very pleased at the prospect of losing their playground to supply a new water wheel at Waterside.

Converting the energy of water to usable mechanical or electrical energy demands a lot of water. The two critical factors are the volume of water available and the drop, or “head”, available between the water inlet, and where it goes back into a tail race or stream. Using figures from Kempe’s Engineers Yearbook 1903 edition, it is possible to see precisely how much water is needed.

For the sake of simplicity, I am following Kempe in assuming that a water turbine is used which is 80 per cent efficient and that a 10ft (3.05m) head of water is available.

In order to produce just 1.1 hp a flow of 7.6 gallons, or 34.5 litres, is needed every second. Generating ten times as much power requires ten times as much water, and if the head of water is less than the figure given, the water supplied has to be increased to compensate.

The illustrations show a water wheel and, unfortunately, water wheels are not often 80 per cent efficient. If the proposed design is an undershot water wheel, then Kempe’s Year-book advises that they are capable of extracting 27-40 per cent of the potential energy in the water, increasing the water needed by a factor of two or even three, pushing it up to a figure somewhere between 15.2 and 22.5 gallons (69 and 102.2 litres) per second, and all for 1.1 horsepower.

Because there is always a minimum five per cent loss in converting mechanical energy to electrical energy, it then becomes clear that generating 10kW of electricity would require 12.82 times as much water as producing 1.1 mechanical horsepower – a fairly staggering 195 to 289 gallons (885 to 1,313 litres) per second!

As these figures indicate, without extensive and very costly water management upstream of the wheel, it is not plausible to suggest that the river at Laneside has enough water available to turn water power into electricity.

Before raising people’s hopes, I am sure that the Todmorden Civic Society will be seeking advice on the scheme they are proposing from a qualified engineer so that they are aware of the full costs of the water wheel and associated water management system, as well as any potential benefits.

Robin Pennie,

Ewood Lane,

Todmorden.