Longbridge Turbine working

The River Derwent changes from millpond flat to all ripples as it drops the few inches over the submerged weir by Derby Council House.

Outside the Council House in Derby work on the newly refurbished Riverside Gardens is nearly complete.  This was originally laid out to provide a setting for the Council House, so it is good that this work is being able to be done at the same time as the Council House is refurbished.  This setting includes the submerged weir, just by the Council House, providing a ripple-affect. 

The water doesn’t drop far over this weir – maybe as little as 6 or 8 inches (15-20cm) but the affect this has on the water is dramatic.  From millpond, mirror-like stillness on the upstream side, below the surface is all ripples.  All this activity is releasing the ‘surplus’ energy due to the level change.

And downstream we can see a larger example of the same affect on the Longbridge Weir. 

Water falling over the weir produces lots of churn and splash as it drops 2.5m (8 foot) the potential (height) energy of the water above the weir turns into movement, heat and noise below the weir.

In the foreground water flows calmly away from the new Longbridge Weir turbine, in background it tumbles noisily down the weir.

But not all the water now flows this way.  The turbine is working, and up to 13 cubic metres of water a second is diverted this way.   The weight of this water dropping the 2.5m turns the new turbine and electricity generator extracting the water’s potential energy and turning most of it into electricity – up to 230kW.  As the water leaves the turbine its energy has already gone, and it flows gently away with hardly a splash.

The electrical power provides electricity for the Council House, with any spare being sold to the grid.

I smile with pleasure and satisfaction when I think of all the engineering, ingenuity and determination required to achieve this one project – and my small role in championing it when I was on the council cabinet.

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