132004.240018.A - Request to change an existing Approval

Current Inundation   Times and Levels

The Hydrology and Water report (2014) titled "Garnet Street Culvert Upgrade Hydraulic Assessment" indicates
that currently Garnet Street experiences the following time of inundation and flow depths:-

Table 1- Current Inundation Times & Peak Flow Depths


Event                                    Inundation time                      Peak Flow Depth (over Road)


2-Year ARI event (39% AEP)               6 hours                              0.5m


10-Year ARI (10% AEP)                    12 hours, 20 minutes                 0.8m


lOO-Year AR111%AEP)                      21 hours                             l.Om


Currently Garnet Street is not trafficable     during any of these rainfall events and is inundated        for extended
periods of time.

The most recent design being proposed and referenced in the Hydrology and Water report 12014) titled
"Garnet Street Culvert Upgrade Hydraulic Assessment" indicates significant improvement of times of
inundation and peak flood depths. Refer Tabie 2 below.

Table 2 - Proposed Inundation Times & Peak Flow Depths


Event                                I   Inundation time                      Peak Flow Depth (over Road)


2-Year ARI event (39% AEP)               Nil                                  Nil

                                         (Approximate 6 hour reduction)


10-Year ARI (10% AEP)                    2 hours, 40 minutes                  0.18m - Safely trafficable

                                         (Approximate 10 hour reduction)      (Peak Velocity-Depth Product      = 0.121
100-Year ARI (1% AEP)                    5 hours, 20 minutes                  0.4m -

                                         (Approximate 16 hour reduction)      (Peak Velocity-Depth Product      = 0.6)
                                                                              (Refer Emergency Vehicle Access
                                                                              references below)


Note that the above-mentioned     improvements/reductions       have been achieved with a blockage factor of 20%
applied to the existing and proposed culverts.

Emergency Vehicle Access

Reference is made to the Australian Emergency Manuals Series Part IV - Skills for Emergency Services
Personnel titled "Manual 8 - Four-Wheel-Dr;ve 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
    2
0.6m /sec.

The velocity.depth product of 0.6m2/sec is provided in Queensland Urban Drainage Manual (QUDM - 2013) and
described as "The praduct of depth d, and velocity v.~ In the kerb and channel should nat exceed O.6m'/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 OAm 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.




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