Home > Cases > Scientific doubt about effects of waterfall mist defeats hydropower scheme

An appeal against a decision to refuse to license a hydropower scheme along the River Clywedog in Dolgellau, north Wales, has been dismissed after the Welsh Ministers’ inspector agreed that there were unresolved questions about a potential link between waterfall mist and the sustainability of rare local mosses.

Natural Resources Wales (NRW) had refused the applications for licences to abstract and impound water at the site due to concerns that the lower river levels could reduce the ‘mist zone’ from cascading water and, in turn, lead to lower humidity levels in the gorge, threatening bryophytes living on rocks nearby. The site is part of a Special Area of Conservation (SAC) designated pursuant to the Habitats Directive. The management plan for the SAC identifies humidity as a key factor governing the condition of the protected mosses.

In its appeal under section 43 of the Water Resources Act 1991, the appellant argued that it had provided more than enough linear statistical evidence to show that there was no longer any reasonable scientific doubt about the lack of connection between river level and humidity, submitting that humidity was overwhelmingly determined by rainfall. NRW contended that a further “multivariate statistical analysis” was still required to remove this doubt and that, until this was done, a precautionary approach meant that the appeal had to be dismissed.

The inspector accepted NRW’s case, agreeing that without a “multivariate approach”, he could not “conclude beyond all reasonable scientific doubt that desiccant intolerant bryophyte species would not be deterimentally affected” [18].

As part of its case before the inspector, NRW provided evidence that a respected academic had shown interest in carrying out the type of complex statistical modelling that it considered necessary.

Gwion Lewis acted for Natural Resources Wales in the appeal. The Planning Inspectorate has issued the decision in English and in Welsh.

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