What are cumulative effects?

In layman's terms, a cumulative effect is where a particular effect (lets call it the noise from a frost fan) is increased by virtue of the fact that there is more than one frost fan operating. The net result being a louder noise.

This becomes significant when considering a resource consent, if the applicant wants to put in four frost fans then the cumulative noise from all four will significantly exceed the noise that would have occurred if only one had been operating.

Normally a frost fan will be restricted in terms of the amount of noise it can produce by a consent that says something like it can only produce 55dBA L10 at 300 metres. Now it stands to reason that if you have more than one frost fan operating and each is operating to that one noise standard then the cumulative noise will be greater than the allowable level.

Oddly enough this has not been the position of applicants wanting to install frost fans or their hired consultants. There has however been a judgment from the Environment Court (Maclean vs Marlborough District Council, 2008) that required the applicant to have the noise from their fans considered and measured cumulatively so that the combined noise needed to be under the specified limit.

There is a useful paper on the topic by Philip Milne here.

The realisation that cumulative effects are real is also carried through to the Western Bay of Plenty District Council ‘Land Use Consent for Frost Control Fans’ form which states that;

If the application is for more than one frost fan on the same property, the technical report is to include the cumulative effects of noise.

and

Council’s policy in previous applications for affected persons is for a 500m buffer for one frost fan. This increases to 600m for two, and 650m for three machines, although Council reserves the right to deem any person affected.