Bushfire Hazard Assessment & Management Plan

Bushfire Hazard Assessment & Management Plan – v2                           NCES REF: ELK 2016-04
Lot 70 on M37807 – 28 Elkhorn Drive, Tewantin




5.3.2 Quantitative Modelling
Quantitative modelling of the potential bushfire conditions that may be experienced within the
vegetation fronting the eastern site boundary has been undertaken to assist in quantifying the
potential risk of impact to the proposed development. The models used comprise industry
standard bushfire equations.

5.3.2.1 Site Specific Input Parameters
Slope = 5º inclining toward site
FDI = 50 (Sunshine Coast)
Surface Fuel Load = 12 t/ha, Total Fuel Load = 16 t/ha (Source: Derived from onsite Fuel Load
Assessment for VU2 – See Section 5.3.1)

5.3.2.2 Formulae
Rate Spread (R) R = 0.0012 *FDI*w *exp (0.069*slope) (Noble et al. 1980)
Where:
R = rate of spread (km/hr)
FDI = Fire Danger Index
W = surface fuel load (t/ha),
Slope = slope of the land with vegetation (degrees)

Fire Intensity I = H*W*R/36 (Byram 1959)
Where:
I = fire intensity (kW/m)
H = heat of combustion (kJ/kg), approximated as 18,600 kJ/kg
R = rate of spread (km/hr)
W = overall fuel loads (t/ha),

Flame Length Lf = (13R+0.24W)/2 (RFS PBP 2001)
Where:
Lf = flame length (m)
R = rate of spread (km/hr)
W = overall fuel loads (t/ha),

5.3.2.3 Modelled Output

(R) = 0.0012 x FDI (50) x Surface Fuel Load (12) x exp (0.069 x slope (5)) = 1.01km/hr

(I) = 18600kj/kg x 16 x 1.01 / 36 = 8.349 kW/m

Lf = (13 x 1.01 + 0.24 x 16)/2 = 8.48m

The results illustrate that the identified Medium hazard vegetation along the eastern boundary
of the site represents potential to exhibit moderate severity bushfire conditions at the time of
assessment. Flame length results infer sufficient flame heights could be output to facilitate a
crown fire within the open eucalypt forest vegetation. It is noted a slope of 5⁰ was selected as
the slope input parameter and that a fire burning along the river bank would predominantly
burn across the contour which is equivalent to near flat conditions. A five-degree slope
increases forward rate of spread by 30% which would have a corresponding significant
influence upon the fire intensity and flame length output results. Therefore, the output results
are considered somewhat exaggerative. Wind velocities, atmospheric conditions, and time
since last fire would also affect bushfire behaviour, either increasing or decreasing potential
bushfire severity.




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