Ridgewood_12-002_Meteorology_L35815BH_221015

Mr David Milligan, W Donald Milligan Pty Ltd                                                 22 October 2015
Re: Response to Issue Raised in Submission Regarding Meteorological Modelling – Proposed Poultry Growing
        Sheds, Ridgewood                                                              Ref: L35815/BH/12-002


The use of the 1.8 metre height wind speed data as a basis for validation of model
prediction of wind speeds and frequency of calm conditions at a 10 metre above ground
level height3 is not considered reliable by MWA Environmental for the following reasons:

    1. The 1.8 metre height anemometer is affected by local vegetation and terrain variations
       which would significantly reduce wind velocities and increase the likelihood of calm
       conditions as compared to a 10 metre height.
    2. Although MWA Environmental has extrapolated the 1.8 metre height wind speeds to
       estimated 10 metre height wind speeds using the common Power Law method based
       upon Irwin Rural wind profile exponents4, this relationship is intended to be applied for
       extrapolating 10 metre wind speeds to greater heights and is not as reliable for
       adjustments to heights so close to the ground surface, particularly for stable
       atmospheric conditions commonly associated with low wind speeds. This is noted in
       the following extract from Australian Standard AS3580.14-2011 - Methods for sampling
       and analysis of ambient air - Part 14: Meteorological monitoring for ambient air quality
       monitoring applications:




A comparison of the CALMET model predicted wind roses for the meteorological grid node
nearest to the weather station location and the on-site weather station recorded wind roses5 is
provided as Attachment 2.

A graphical comparison of the wind direction distributions for the CALMET model and the on-
site weather station is provided as Attachment 3.

Given the natural variability in wind patterns year-to-year and that the monitoring data is for
2014/2015 compared to the 2008 model year, the overall distribution of wind directions
predicted by the model on an annual and seasonal basis is considered to:

    1. Correlate well to the observed on-site wind directions; and
    2. Capture key local and seasonal characteristics.

As expected for the reasons stated above, wind speed data derived from the on-site weather
station 1.8 metre anemometer height indicates more frequent occurrence of wind speeds
below 0.5 metres per second. This is largely considered to be an artefact of the wind speed
measurement height and the local surface roughness in proximity to the anemometer rather
than demonstrating a model performance issue. The wind roses demonstrate acceptable
model prediction of frequencies of higher wind speed categories where the shortcomings of the
wind shear extrapolation method are less significant.


3 As per model predictions and Australian Standard meteorological station guidance
4 Which are generally acknowledged to be imperfect for rural sites with high surface roughness such as the
poultry farm site
5 Wind speeds extrapolated to 10m above ground level height by the common Power Law method based upon
Irwin Rural wind profile exponents




                                                       5