Noise mitigation should be a key consideration in any hydroelectricity project, independent environmental consultants Atmos Consulting says.
Hydro is often seen as relatively benign compared to some other technologies like onshore wind, but the firm’s lead acoustician Jim Singleton says this means noise assessments are sometimes overlooked, resulting in failure to get planning permission, or expensive retrospective soundproofing.
“All hydro schemes require a noise assessment, even those not subject to an Environmental Impact Assessment. It’s not just a case that bigger turbines are noisier,” says Mr Singleton.
A major noise source in hydro plants is not the turbine or generator, but the mechanical ventilation used to cool the turbine house, which is often just a fan and louvre opening, he says.
“Sometimes it may simply be a case of putting the opening on another side of the building or buying a quieter fan. Either way, it’s always cheaper to do this at the outset rather than retrospectively.”
Acoustic louvres that absorb sound, and/or a silencer on the fan can help, he says. Silencers must be carefully matched to the frequency range specified on the fan. “If not, a silencer could result in ‘tonal’ noise, which can be more annoying than the ‘broadband’ noise from no silencer.”
Attention should also be given to turbine house construction. Concrete block work does a good sound-proofing job, but roofs and doors need to be equally soundproof, by using appropriate insulation or soundproof sheeting, he says. Half-burying turbine houses can also help but screens of hedges or trees do very little apart from reducing visual impact, he adds.