Download TEMPERATURE INVERSIONS IN DEEP OPEN-CUT MINES?

TEMPERATURE INVERSIONS IN DEEP OPEN-CUT MINES?
Mark F. Hibberd, Jim Hondros
Centre for Australian Weather and Climate Research, CSIRO Marine & Atmospheric Research, Aspendale 3195
BHP Billiton, 55 Grenfell St, Adelaide 5000
Keywords: Stability, Froude number, Dispersion, Dust
Do temperature inversions or strong
stable
conditions occur in deep open-cut mining pits? This
question is important for modelling the dispersion of
pollutants such as dust or radon in deep pits such
as the proposed Olympic Dam mine in SA, which is
planned to be almost 1 km deep.
It is well known that strong nocturnal inversions
occur in valleys and mountain basins on calm, clear
nights (e.g. Hibberd 2003, Clements et al 2003)
and that they can be caused by radiation cooling
and/or cold air drainage, but there are
almost no
data on the nocturnal meteorology in deep open-cut
mines.
This study measured vertical temperature profiles
in two 300 m deep mines in Western Australia on
25 nights during autumn and winter.
Whiteman et al (2004) showed that in night-time
stable conditions, measurements on the sidewall of
a basin agree well with those from a tethersonde in
the middle of the basin. Thus, in
this study, data
were collected using meteorological instruments
mounted on a mine utility vehicle (Figure 1), which
travelled on mine access roads between the top
and bottom of the pit. A Vaisala PTU300 datalogger
in the cab stored the data every 10 seconds. Height
was derived from the ambient
pressure
measurements.
typically constant thr ough the depth of
the pit
(e.g. Figure 2 ). Stable conditions were measured
on 25% of the nights sampled. The uncertainty in
the gradients was estimat ed at 0.002 K/m. There
was no evidence of significant capping inversions in
any of the measurements.
Analysis in terms of Froude
number Fr = U/(Nh)
where U is pit-top wind speed,
N is the BruntVäisälä frequency, and h is the depth of the pit,
showed that stable conditions were only observed
for Fr < 1, i.e. this criterion corresponded to poor pit
ventilation.
It is hoped that publication of
this paper might
encourage others to share any results they have
that are relevant to dispersion in deep open-cut
pits.
700
Average potential
temperature gradient 1°C/100 m
Mt Whaleback pit
temperature profiles
at time shown
23-24 July 2009
Descending
Ascending
600
Reduced Level (m)
1. Introduction
500
400
1900 h
0400 h 0200 h
17
18
2230 h
2000 h
1800 h
19
20
21
Potential temperature (°C)
22
23
Figure 2. Examples of stable temperature profiles
References
Figure 1. Sensors on side of roof rack on mine
utility vehicle.
2. Results
A range of potential temperature gradients from
neutral to a maximum of 0.01 K/m was observed,
CASANZ 2011 Conference - Auckland - 31 July - 2 August 2011
Paper 214
Clements, C.B., Whiteman, C.D., and Horel, J.D.
2003. Cold-air-pool structure and evolution in a
mountain basin: Peter Sinks,
Utah. J. Appl.
Meteorol. 42, 752-768.
Hibberd, M.F. 2003. Nocturnal dispersion
meteorology in an urban valley.
Clean Air &
Environ. Qual. 37 (4): 34-37.
Whiteman, C.D., Eisenbach, S., Pospichal, B., and
Steinhacker, R. 2004. Comparison of vertical
soundings and sidewall air temperature
measurements in a small alpine basin. J. Appl.
Meteorol. 43, 1635-1647.
Assistance from Dylan Bilske, Simon Hilder and
Phillip Bryant is gratefully acknowledged.
CASANZ 2011 Conference - Auckland - 31 July - 2 August 2011
Paper 214