Work on a controversial £5m project to replace an historic reservoir spillway starts next month.

Yorkshire Water will start work on the spillway at Butterley reservoir early next month.

The stone spillway, designed by Thomas Hawksley, is an incredible feat of engineering and was completed in 1906. It controls the flow of water from Butterley reservoir, safely ensuring it does not overtop and damage or erode the embankment.

Butterley Reservoir Spillway, Marsden.

A previous inspection of the spillway by an independent Panel Engineer highlighted the need to adapt the spillway to ensure it continues to meet with legislation, in particular, the Reservoirs Act 1975.

But many objected to the plans and fought a vigorous campaign to try and ensure the historic spillway was retained, in whole or in part.

Yorkshire Water’s contractors, Mott MacDonald Bentley, will raise the spillway walls and replace the steep section (towards the middle of the spillway) with a straight slope to ensure flood waters are contained within the channel.

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Lee Laherty, Yorkshire Water Project Manager said, “We know that the spillway is a much-loved local landmark and we’ve worked hard to design a solution that’s sympathetic to the local surroundings , whilst ensuring it meets legal requirements.

“We are going to replicate the existing small steps within the spillway, retain two thirds of the existing spillway walls and re-use coping stones where possible. We’ll clad the raised walls with natural sandstone and hope to retain the majority of existing keystones.”

The huge engineering project will take until the end of 2017 to complete. Some of the local footpaths around the reservoir need to be temporarily diverted so the work can be carried out safely. The diversion routes will be clearly signposted.

Butterley Reservoir Spillway, Marsden.

Colne Valley MP, Jason McCartney, said: “I’ve been urging Yorkshire Water to engage with the local community and interest groups for a number of years now regarding this important project.

“I’m fully aware of the sensitivity around the impact to the spillway. I hope they continue to listen to feedback and support local initiatives whilst they’re working in the area.”

Mr Laherty added, “We will continue to talk to the local community about key events, like the delivery of the large cranes needed to remove and replace the coping stones, and we are definitely planning to support local events whilst we are working in Marsden.”