2014-10-14 Planning & Organisation Committee Agenda - Pages 1 - 50

PLANNING & ORGANISATION COMMITTEE MEETING AGENDA                            14 OCTOBER 2014


Emergency Vehicle Access
Reference is made to the Australian Emergency Manuals Series Part IV - Skills for Emergency
Services
Personnel titled "Manual 8 - Four-Wheel-Drive Vehicle Operation". Section 5.26 to 5.35 details
the safe operation of four wheel drive vehicles during a water crossing operation. This section
discusses the required preparation for deep water crossing whereby "If the water depth is greater
than about 750mm, prepare the vehicle as follows ..” This section of the manual indicates that
four wheel drive emergency vehicles can safely navigate through water crossings less than
750mm deep provided the velocity-depth product is less than 0.6m2/sec.
The velocity-depth product of 0.6m2/sec is provided in Queensland Urban Drainage Manual
(QUDM - 2013) and described as "The product of depth dg, and velocity vave in the kerb and
channel should not exceed O.6m2/sec (Engineers Australia, 20l0) to reduce hazard for
pedestrians within the roadway."
The modelling results identified in the Hydrology and Water report (2014) titled "Garnet Street
Culvert Upgrade Hydraulic Assessment" indicate that the most recent design case will incur flow
depths of 0.4m and velocity-depth product of 0.6m'/sec during the 1%AEP. On this basis, an
emergency vehicle can safely negotiate Garnet Street during a major storm event.


Bridge Option Analysis
Consideration has been given to a proposed bridge across Cooroy Creek but this option has
been dismissed given the flood mitigation measures that are provided by the culverts.
The culverts in their proposed form will regulate flows to ensure upstream and downstream
conditions are "balanced" to a point where non-worsening of private properties is achieved. The
construction of a bridge effectively removes this mitigation and has the potential to increase
flooding downstream of Garnet Street.
Furthermore, given the substantial floodway width across Garnet Street and the physical
constraints of the Cooroy Creek alignment, construction of a bridge is not considered a viable
option.


Blockage Factors
Queensland Urban Drainage Manual (QUDM - 2013) provides a suggested blockage factor of
0% for a clear opening greater than 3.0m. Table 10.4.1 - Suggested blockage factors for culverts
highlights that a design blockage value of 20% should be assigned to culverts less than 3.0m in
height or less than 5.0m width.
A 20% blockage factor is considered appropriate given the culvert sizes and site characteristics
and has been adopted for modelling purposes by Hydrology and Water when undertaking the
flood modelling analysis.
In accordance with best practice, a sensitivity test has also been carried out using a blockage
factor of 50% in order to gain an understanding of any additional flood risk associated with a
higher blockage scenario. This sensitivity test is documented in the Hydrology and Water report
(2014) titled "Garnet Street Culvert Upgrade Hydraulic Assessment".




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