Essential work to protect against the potential flooding of Llyn Mair reservoir during major weather events has been given the go-ahead.

The refurbishment and installation of a new siphon system at Tan Y Bwlch, Maentwrog, was agreed with conditions, by Eryri National Park’s planners.

Officers said the work was “essential” but not “major,” at a planning and access committee meeting on 25 February.

A report said Llyn Mair “was constructed by building a dam across the top of a little valley on the eastern side of the historic park to impound water in an area of some 6.5 hectares”.

It falls inside the boundaries of the Slate Landscape of north-west Wales – World Heritage Site.

“The proposed works are to provide a siphon, so the reservoir is better equipped to deal with major weather events, so it is possible to safely lower the level of the reservoir,” the meeting heard.

Officer Aled Lloyd described how it was in an area with a 1 per cent chance of flooding from rivers in a given year, including the effects of climate change, adding: “Given the proposal has been designed to ensure greater safety in a major weather event, officers are satisfied there is justification for the proposal and it accords with policy.”

He said the siphon would be located partly inside the reservoir and partly inside the original reservoir spillways and “will not alter the way that this historic park and landscape will be experienced, understood and appreciated”, and “there will be no visual, significant impact on the area and no impact on Plas Tan Y Bwlch historic park and garden or on the historic universal value of the World Heritage Site”.

The proposal was “acceptable” and a recommendation to approve given.

The application was agreed with conditions including having an environmental plan when the work is carried out, to assess impact.