The Magnificent Butterley Reservoir Spillway is the Country’s Only Listed Spillway.  Yorkshire Water Plan to Demolish it.

Butterley Reservoir is the lowest of the reservoirs in the Wessenden Valley. The magnificent spillway (also known as the overflow) is a remarkable landscape feature known and loved by villagers and visitors to the area. Yorkshire Water is planning extensive works which will result in everything that is special about the spillway being lost.

As well as being much loved, the spillway is an important part of our national heritage – PLEASE HELP US TO SAVE IT!


Yorkshire Water (YW) is planning to make alterations to the spillway at Butterley Reservoir. Yorkshire Water are planning to:

Works upstream of the stepped cascades

  • The existing stone steps would be removed and replaced with concrete, with a stepped finish similar to that of the masonry that would be removed. The keystones would be retained;
  • The left-hand wall would be kept as existing. The large pillar at the downstream end would be raised and the surface made flush with the internal wall of spillway;
  • The right hand wall and pillars would be retained but raised. The surface would be made flush with the internal wall of spillway. The wall facing the inside of the raised spillway would be stone. The existing stone copings would be re-used; and
  • Edge protection and safety fencing provided above the spillway walls.

Works on the cascades

  • The stepped cascades (steep sections) would be replaced with a new concrete base incorporating a revised profile similar to the upstream section. New keystones would be incorporated into the new base to give a stepped appearance similar to the upstream section of the spillway. This would provide a constant gradient down the length of the spillway;
  • Provision of new walls (both sides) to suit the new base profile. The wall height would be increased and the ground raised locally up to the raised wall. Stone would face the inside of new spillway walls. Where retained the surface of pillars would be made flush with internal wall of the spillway. New coping stones would be provided;
  • The existing masonry steps next to the spillway would be re-located away from the spillway; and
  • Edge protection and safety fencing provided above the spillway walls.

Works to the clay core

  • Raising of the clay core over the full length of the reservoir. On completion of the works, the embankment crest would be reinstated to existing levels.


The works are needed to comply with the Reservoirs Act of 1975. Yorkshire Water say this act has been changed more recently which is why works are only being undertaken now.

The reservoirs are inspected by Yorkshire Water for safety every year and every 10 years by an independent auditor. The last independent audit identified safety work which is required at the reservoir. The work required is to ensure that excess flood water can flow from the reservoir without putting the dam banking in danger of collapse. The likelihood of such a catastrophic flood occurring would be around 1 in 20,000 years. In other words, we would have to have days of torrential rain, falling onto soil that couldn’t hold any more water, with the water flowing into a completely full reservoir and for everything possible to fail and go wrong so that the spillway would be subject to the greatest hydraulic forces.


Yorkshire Water have built a model of the existing spillway in a testing facility and poured water down it to replicate such a flood. What happened was:-

  • The water cascaded down and hit the stone pillars which are partly located in the channel. The water was forced upwards when it hit these.
  •  As the water came down, it hit the relatively level sections which have a more gentle gradient and again the water was forced upwards.
  •  The effect of the change in direction of the water created big forces on the sides and bottom of the spillway which could be enough to lift the stones that currently line it (this happened in 2002 when some stones were moved out of position).
  • The force of the water could be enough to create a hole in the side walls which could lead to the erosion and collapse of the bank.




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