Revised Civil Engineering Response Cover Letter

Page 2

RESPONSE
Please refer to the attached drawings which demonstrate the underground services
adjacent to the subject site driveway and the recently constructed neighbouring driveway.
Drawings are coordinated between disciplines for the response to this IR.



ISSUES 16, 17 & 18
Council has a number of concerns with the proposed heavy vehicle bay and the heavy
vehicle path through the site:
   • The architectural plans indicate a “semitrailer bay” while the engineering plans
        indicate a vehicle manoeuvring path for a Heavy Rigid Vehicle (HRV)
   • The proposed semitrailer bay appears to block access to areas of proposed Unit
        11
   • The heavy vehicle swept path plans does not indicate the required vehicle
        accessing the proposed service bay and appears to conflict with landscaping
        areas and extends under the roof line at a number of locations

Information Required:
16. Provide amended architectural and engineering plans that indicate the parking and
manoeuvring for a semi-trailer sufficient to demonstrate compliance with The Noosa Plan,
Driveways and Parking Code, PO6 (AO6.1) and PO7
17. Provide additional detail on how the access to the adjacent unit is not significantly
impacted by a heavy vehicle parked in the service bay
18. Provide amended plans of the heavy vehicle manoeuvring path that demonstrates
that the path is clear of landscaping areas and in those locations where it extends under
the roof line, provide sufficient detail to demonstrate that vertical height clearances are
available



RESPONSE
Item 16. Please refer to the attached drawings (2123 R10 & R11) for vehicle swept paths.
Additionally, swept paths for larger Articulated Vehicles have been run on the incidental
chance that a different AV enters the site. This study was done due to the proximity of the
subject site to the Bruce Highway. The outcomes of this have been communicated to the
developer and explained that any vehicles larger than the design vehicles will require one
reversing manoeuvre (typically into site) and there is ample roof in the Taylor Court road
pavement to achieve this.

Item 17. The on-site semi-trailer service bay is positioned clear of the entry points to Unit
11 and adjacent to the outdoor space allocated to Unit 12. Refer architectural plans for
details

Item 18. Please see attached update drawing 2123/R10 (Rev C) which shows the HRV
path through the subject site without impacting on buildings and landscape spaces. The
building roofs are typically at 6-7m high as per the architectural drawings so there is no
clash between the HRV and roof overhangs / awnings on site.




2123 – 3 Taylor Court, Cooroy                                                               2
CL/cl

Page 3

ISSUE 19
The earthwork cross sections do not appear to extend into the adjoining properties to
the east and indicate the recently constructed access driveway and surface levels

Information Required:
Indicate on the adjoining driveway on the engineering cross section plans and also include
on the plans any measures necessary to protect the structural integrity of the driveway
and the adjoining property

RESPONSE
Please refer to the attached updated civil drawings which show the as constructed levels
of the adjacent driveway. It is confirmed from the subdivision works that the driveway is
typically 0.8m back from the cadastral boundary and whilst there is a sandstone boulder
wall (1 block high) along part of this boundary, the maximum step is 0.4m and not in the
locations of where the earthworks cross sections are cut. To address this, Top of wall and
bottom of wall RLs (TOW, BOW) are given on drawing 2123 - R04 (Rev C). None of the
proposed height changes are more than 600mm and, given the setback to edge of
driveway concrete, means the adjacent driveway pavement will not be undermined. Exact
construction methodology for footings in this area is to be managed as part of the
structural engineering works. It is proposed that a condition is included with any decision
notice to confirm that development works would not undermine or impose loads
unaccounted for to the adjacent lot driveway pavements.



ISSUE 20

Information Required:
Provide updated OPW drawings for the bioretention basin which address the following
issues:
20.1 Provide survey for the existing drainage system that the bioretention device will
connect into (i.e. existing pit IL and pipe diameter and outfall IL). Confirm that the basin
subsoil drains will drain effectively.
20.2. Show the proposed subsoil drain layout in plan view.
20.3. Inconsistent level information is shown in the boxed text and on the sections for the
bioretention on drawing R07 – resolve inconsistencies

RESPONSE
Item 20.1. The invert of the proposed stormwater pit was confirmed on site (measured by
engineer) to be 1.65m deep. This provides sufficient depth for the proposed detention
tank connection.
Item 20.2. Please refer to the attached drawing 2123/R07 for updated subsoil layouts
Item 20.3. Please refer to the attached drawing 2123/R07 for updated RLs.



ISSUES 21 & 22

Information Required:
21. It appears that a detention basin was provided within the downstream drainage
reserve as part of the original development of the industrial estate. Consider whether the
detention tank proposed is necessary given this downstream infrastructure.
22. If the detention tank is retained, address the following:

2123 – 3 Taylor Court, Cooroy                                                              3
CL/cl

Page 4

22.1 Sizing appears to be small given the land use change. This may be due to the low
initial loss values adopted for pervious surfaces in the model. Provide further information
of how rational method flows were calculated, including tc estimates. Provide, as a
comparison, detention sizing based on QUDM recommended initial pervious loss rate of
20mm.
22.2 Provide survey for the existing drainage system that the detention tank will connect
into (i.e. existing pit IL and pipe diameter and outfall IL).
22.3 The outlet structure from the detention tank is unclear. Is the final outlet an upstand
225 dia pipe as seems to be shown? If this is the case won’t the upstream orifices all be
drowned?
22.4 Regardless of the above, for whatever outlet pipe is selected for the detention tank,
demonstrate that the final outlet won’t drown the orifices and that the assumptions in the
model will be met (eg. The outlet pipe from the tank should be set down lower than the
lowest orifice so that it does not become drowned)
22.5 An access chamber to the detention basin outlet structure is shown and is supported.
However why is the lid on this chamber shown as a grate rather than a sealed lid? Won’t
the grate allow flows to bypass the detention tank?

RESPONSE
Item 21. From our analysis of Council assessment of Lot 5 Taylor Court, there appears
the need for a detention basin on the subject site to account for high peak stormwater
discharge to the downstream network. Unfortunately, we do not have the report or
correspondence to confirm the downstream basin provides detention of flows to this site
and from conversations with Council staff, are of the opinion it provides a water quality
function only. If Council has access to this drainage study and basin design report, we
would appreciate a copy. Despite this, it is acknowledged that any downstream basin
structure will provide some form of flow mitigation to runoff entering the basin.
Item 22.1. Rational method calculations were provided in Appendix C of the stormwater
management report 2123-SBSMP-01. Tc is calculated using the friends eq’n for overland
sheet flow from QUDM. Initial and continuing loses for the XP Storm model were then
adapted to these Rational method results as per Tables 4.2 an 4.3 in the report and Figure
4.1. The pre-development rational method values were consistent with the XP Storm
outputs however they were typically 5% less in magnitude so the existing case rational
method results were used as the base case to compare against the post development
(mitigated) XP Storm model results. This builds in a conservative 5% overdesign into the
detention model.
Item 22.2. It is recognised that The invert of the existing pit was not included in the original
site survey. Barlow Shelley attended site to measure the depth of the SW pit and confirm
it is 1.65m deep. This should be confirmed prior to construction but established that there
is sufficient depth to reliably connect the stormwater system to this existing pit structure
and outlet pipe.
Item 22.3. The hydraulic orifice controls are mirrored into the wall of the riser pipe. This
was not clear on the original plans so please refer to the updated drawing 2123/R07 (Rev
C).
Item 22.4. The outlet pipe from the tank exits the detention structure through the floor.
The lowest pipe orifice is the tank invert so the system cannot become permanently
drowned in function. There is a second maintenance access in the pipe riser and overflow
area for maintenance to clear this space of debris if required. In the event this area is not
maintained and a significant storm (or design storm grater than the 1% AEP) is
experienced on site. A weir to the south side of the bioretention basin provides overflow
redundancy so the drainage system inside the development site does not back up and
enter the units.



2123 – 3 Taylor Court, Cooroy                                                                 4
CL/cl

Page 5

Item 22.5. As per response to Item 22.3 above, the overflow zone in the detention basin,
which includes the riser pipe) is for stormwater to get into the tank and be attenuated by
the orifices in the riser pipe. This could be done without the inclusion of an internal baffle
wall to the tank but creates the possibility of more debris against the riser pipe outlet and
higher dependence on maintenance for the system to function properly. The flows through
the riser haven’t bypassed the detention tank, they are just reduced in unattenuated
volume into the overflow chamber for the above reasons. The design intention is to build
in some longevity and reduced maintenance practicality. The internal baffle wall can be
removed if it concerns Council how the tank will function.



We trust this satisfactorily addresses the above issues raised in Council’s Information
Request letter.




Yours sincerely,




____________________________________________
CAMERON LANDRETH – DIRECTOR (RPEQ 19358)
BEng (Hons), NER, RPEQ
For and on behalf of:
BARLOW SHELLEY CONSULTING ENGINEERS (AUST) PTY LTD
Enclosed:
Updated civil drawings Lot 4 Taylor Court, Cooroy (ref: 2123 R01-R11)




2123 – 3 Taylor Court, Cooroy                                                               5
CL/cl