November 2004 (PDF 11.6 MB) - Barrick Gold Corporation

eceiver component drainage-flow windspeed for those receivers where applicable.(See below for applicability of drainage-flowwind.) For more information see Appendix C.Arid and semi-arid areas (annual average rainfall lessthan 500 mm):Strong (G-class stability category) inversions• 8°C/100 m temperature inversion strengthfor all receivers, plus a 1 m/s source-toreceivercomponent drainage-flow windspeeds for those receivers where applicable.(See below for applicability of drainage-flowwind.)Applicability of drainage-flow windThe drainage-flow wind default value shouldgenerally be applied where a development is at ahigher altitude than a residential receiver, with nointervening higher ground (for example, hills). Inthese cases, both the specified wind and temperatureinversion default values should be used in thenoise assessment for receivers at the lower altitude.B. Using direct measurementWhere the proponent rejects the default values andwishes to use alternative values based on directmeasurement, use the procedure outlined in AppendixE.(Note: Wind data should be collected at 10 mheight.)Step 4:Assess the expected impactThe increased noise level predicted under inversionconditions is then compared with the projectspecificnoise levels to determine whether any noiseimpacts are expected. Noise impacts are likelywhere exceedances of the project-specific noiselevels are predicted.5.3 Wind effectsThe effects of gradient wind on noise levels alsoneed to be accounted for when assessing the impactfrom a planned development. Gradient wind differsfrom the drainage-flow wind associated withtemperature inversions:• drainage-flow wind is the localised drainageof cold air under the influence of the localtopography, and travels in one direction only(direction of decreasing altitude)• gradient wind is the regional winddetermined by synoptic factors (high andlow-pressure systems), and may originatefrom any direction.Wind data are usually relatively easy to obtain, andwind roses are commonly used in most environmentalimpact assessments. Unlike temperatureinversions, gradient winds may cause impactsduring any assessment period (day, evening,night)—not just the night period. Hence the assessmentof these effects should consider all assessmentperiods.5.3.1 When do wind effects need to beassessed?Wind effects need to be assessed where wind is afeature of the area. Wind is considered to be afeature where source-to-receiver wind speeds (at 10-m height) of 3 m/s or below occur for 30 per cent ofthe time or more in any assessment period (day,evening, night) in any season. This differs from theprocedure used with temperature inversions, in thatthe 30-per-cent occurrence applies to all seasonsand each assessment period—and not just thewinter season and night assessment period. Thereare two ways to assess wind effects:• Use a wind rose to determine whether windis a feature based on the frequency ofoccurrence and wind speed. In doing this,take care to assess the source-to-receivercomponents of wind that are relevant.• Simply assume that wind is a feature of thearea (foregoing the need to use a wind rose)and apply a ‘maximum impact’ scenario.5.3.2 What wind speed should be usedwhen assessing noise impacts?Wind is considered in two ways; the wind near theground at the microphone position, and the windaloft at 10 m above the ground.When wind near the ground increases its speed itcan increase ambient noise levels by rustling foliageand creating turbulence when passing over orNSW industrial noise policy34