Bushfire Hazard Assessment Management Plan v2 - 434 Lake Cooroibah Rd Lake Cooroibah v1 · RAL26/0015

Bushfire Hazard Assessment & Management Plan v2                                       NCES REF: J001445
434 Lake Cooroibah Rd Lake Cooroibah, QLD


4.3       Bushfire Hazard Sub-Units
Plan BF02 – Sub-Units divides the assessment area into sub units based on in-situ slope and VHC
conditions. The patch and corridor filtering process detailed in BRC 2019 Section 4.2.6 was then
applied to any eligible sub units. Flamesol modelling was undertaken for each remaining sub unit
host to Prone Type 1 bushfire prone vegetation to determine its Potential Bushfire Intensity class.
Prone Type 2 (Grassland fire) VHCs including VHC 40.4 & Prone Type 3 (Low hazard) VHCs
including VHC 41.4, 42.6 and 43.6 are considered non-bushfire prone VHCs as per Section 7.5.2,
7.6 & Figure 14 of QFES Bushfire Resilient Communities (2019). Therefore, these VHCs are
typically considered low potential bushfire intensity areas for assessment purposes and generally
require no further investigation. Note, there is nonetheless an inherent risk of grassfire in VHC 40.4.

4.3.1      Patch and Corridor Filtering
The patch and corridor filtering process under Section 4.2.6 of the BRC was applied to remove /
downgrade narrow corridors and small patches of hazardous vegetation.
No patches were eligible under Step 1 (<1ha patches).
No patches were eligible under Step 2 (effective fuel load reduction of patches 0.5-3ha).
Several <50m wide corridors of VHC 22.1 and 9.1 were eligible under Step 3 (removal of narrow
corridor elements <50m wide) and were removed.
Following application of Steps 1-3, two residual Prone Type 1 hazardous vegetation fragments (1 x
VHC 22.1 and 1 x 22.1 / 9.1) remained which measured <0.5ha. These fragments are isolated within
a surrounding VHC 41.4 low threat matrix representing low hazard conditions (i.e. <4,000 kW/m
following the Step-2 adjustment). In accordance with BRC 2019 Section 4.2.6 Step 4, isolated
hazardous fragments <0.5 ha are below the minimum mapping unit for reliable hazard classification
and are therefore downgraded/reclassified to Low Hazard (not bushfire prone). The isolated
fragments measuring <0.5ha were subsequently downgraded to Low Hazard.
Following application of Section 4.2.6 of the BRC 2019, three Prone Type 1 hazardous sub units;
SU1a, SU1b and SU2, remain in the assessment area. SU1a and SU1b exhibit the same VHC and
slope conditions but differ based on flame width.

4.3.2      Flamesol Modelling
Quantitative modelling of the potential bushfire conditions that may be experienced within the
confirmed Prone Type 1 hazardous sub units; SU1 (a, b) and SU2, has been undertaken to to
determine Potential Bushfire Intensity classes and inform necessary building setback requirements.
The models used comprise industry standard bushfire equations which have been built into the FPAA
endorsed FLAMESOL computer model. FLAMESOL allows numerous input variables to be adjusted
including fuel loads, fire danger index, site slope, and distance to vegetation. FLAMESOL uses the
following algorithms:
      •    Rate of Spread – McArthur (1973) and Nobel et al. (1980)
      •    Flame Length – NSW Rural Fire Service (2001) and Nobel et al. (1980)
      •    Elevation of Receiver – Douglas and Tan (2005)
      •    Flame Angle – Douglas and Tan (2005)
      •    Radian Heat Flux – Drysdale (1999), Sullivan et al. (2003) and Douglas and Tan (2005)
The FLAMESOL Minimum Distance calculator has been used and comprises an AS 3959:2018
Method 2 (Appendix B) based calculator which can determine a suite of bushfire behaviour variables
including the minimum distances required to achieve a range of different radiant heat level
exposures.
Fuel load inputs have been drawn from the Vegetation hazard class descriptions and 80th percentile
potential fuel load data set presented in Planning for Bushfire Resilient Communities (QFES 2019)
and, where applicable, take into account fuel load reduction protocols identified in Step 2 of Section
4.2.6 of BRC, 2019.



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