November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

around structures. At higher wind speeds, the noiseproduced by wind will drown out noise from mostindustrial and transportation sources. Wind canalso create extraneous noise on noise-monitoringequipment; an upper limit of 5 m/s at the microphoneposition is commonly applied during noisemeasurement to reduce this effect.Where wind speeds increase with height there is aneffect that is analogous to temperature inversionsbut restricted to localities downwind of the noisesource. This effect is represented by the wind speedand direction measured at a 10 m height above theground. The 10-m wind may either be a drainageflow wind associated with an inversion or a gradientwind. The link between the near ground windand the 10-m wind has been described as a powerlaw relationship. This relationship can be complexand can depend on site factors such as the surfaceroughness and the stability of the atmosphere. Thismeans that the 10-m wind cannot, as a general rule,be accurately derived from wind velocity measurementsnear the ground and vice versa.In summary:source, but may not increase ambient noise levels tothe point where they mask noise from the sourceand make it unnoticeable. A 10-m wind of 3m/s isalso unlikely to be associated with near-surfacewinds of a strength able to cause increased ambientnoise levels that would mask increased levels ofnoise from the source.Where there is 30 per cent or more occurrence ofwind speeds below 3 m/s (source-to-receivercomponent), then use the highest wind speed(below 3 m/s) instead of the default.Where there is less than a 30 per cent occurrence ofwind of up to 3 m/s (source-to-receiver component),wind is not included in the noise-prediction calculation.• Noise can be increased by wind.• Wind can create high ambient noise levels.• Wind can create extraneous noise on noisemonitoringequipment.• The near-surface wind and the 10-m windcan cause different noise effects, so that bothneed to be assessed.• The near-surface wind relates to effects on thenoise monitoring equipment and noisegenerated through mechanical interactionwith trees and other obstructions, whereasthe 10-m wind relates to sound-waverefraction through the atmosphere, similar toinversions and its consequent effects on noiselevels.• A significant wind effect near the ground atmicrophone height does not necessarily meanthat a significant wind effect will occur at10 m (and vice versa).A default wind speed of 3 m/s (at 10-m height) isproposed for assessing noise impacts caused bygradient winds. This wind speed can noticeablyincrease noise received down-wind of a noiseNSW industrial noise policy35