2020.11.30 - Response to further RFI - OPW200145

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Traffic Engineering

Item 7 – Condition 17
Condition 17 requires private Road C to have a 12m carriageway having 1.5m on-road cycle
lanes. The normal interpretation of that is a 12m kerb to kerb road, including 1.5m cycle lanes on
each side, leaving the central 9m for traffic in each direction.

Stockwell Response

As per discussions with Council’s traffic engineering consultant and Council planning officers, we have agreed
on a cross section which achieves the intent of both conditions, 17 and 37.




                                       Figure 1: Road C Cross Section

In comparison to Figure 6.4.1.5, the parking lane is reduced from 3.5m to 3.0m wide and the traffic lane is
increased from 4.0m wide to 4.5m wide (as a dedicated 3.0m vehicle lane and 1.5m cycle lane). This solution
provides the dedicated cycle lane and ensures the road does not present as two-lanes each way with a cycle
lane to the edge and no on street parking. Build outs can still occur in the parking lane and can then be
coordinated with the future developments of Lots 3 and 7. This way, the ultimate road width is constructed
now and lanes are established with the only changes being build-outs which can easily be accommodated
without disruption to road users and cyclists at a later date. Please refer to Barlow Shelley Drawings 1856-
R68 E.

Item 8 – Condition 24 d

The proposal to require pedestrians to “dog leg” across Hofmann Drive is unsatisfactory. The path
should be continuous along Hofmann Drive as required by the condition.

Stockwell Response

As per discussions with Council’s traffic engineer, the pedestrian footpath on Hofmann Drive has been
extended along the frontage of Covenant J to achieve compliance with Condition 24 d.




                                  Figure 2: Barlow Shelly Drawing R37 - E

To enable this to occur, the bioretention treatment device in this location has been moved behind the road
reserve. Covenant J allows for stormwater treatment structures with it, as long as this is approved by the
Covenantee in writing under a Management Plan. We attach a copy of the executed Covenant and refer your
attention to Clause 4.1 (b). Please refer to Barlow Shelley Drawing R37-E.
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Item 9 – Grading of Hofmann Drive and Road B

The Barlow Shelley letter of 16 October 2020 indicates that this item has been addressed by flattening
the grades to 6% in accordance with Austroads. This has been done for Road B, but the longitudinal
section for Hofmann Drive still shows a grade of 9% down from the roundabout. This needs to be
rectified.

Stockwell Response

The longitudinal section for Hofmann Drive has been regraded to 6%. Please refer to Barlow Shelley
drawing 1856 R48-E.

Item 11 – Diameter of Roundabout Central Islands

The proposed roundabout dimensions are for a 12m central island radius, with a 12m circulating
carriageway, thus having an outside radius of 24m. The proposed 12m circulating carriageway is too
large for a single lane roundabout, and is the carriageway width that would be provided for 2-lane
roundabout. For reference, Austroads 4B, Table 4.3 indicates that for a roundabout having an outside
diameter 48m (24m radius) as proposed, the circulating carriageway width should be approximately
7m. It is thus requested that the central island radii of the two roundabouts be enlarged as much a
possible within the currently proposed roundabout footprints (as close to the 7m circulating
carriageway width suggested in Austroads 4B, Table 4.3), so as to satisfactorily accommodate the
design vehicle (articulated vehicle) while also constraining and deflecting paths through the
roundabout as much as possible for all vehicles.

Stockwell Response

The new Northern and Southern roundabouts have been widened from a 12m central island radius to a 15m
central island radius. This results in a 9m circulating width and allows for a 19m Articulate Design Vehicle to
satisfactorily manoeuvre both roundabouts. Please refer to Barlow Shelley drawings 1856-T12B – T14B for
swept path analysis confirmation.




    Figure 3: Barlow Shelley Drawing 1856-T12 B              Figure 4: Barlow Shelley Drawing 1856-T14 B
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Item 13 – Pedestrian Facility across Road C near Hofmann Dr

It has not been satisfactorily demonstrated that the pedestrian facility across Road C at the Hofmann
Drive roundabout can’t be located at the appropriate location 6m clear of the circulating carriageway
of the roundabout. The proposed location of the facility further north-east would only be accepted if
the crossing location 6m from the roundabout is unachievable.

Stockwell Response

The pedestrian facility across Road C from the southern roundabout has been repositioned further to the
south with an angled orientation across Road C to avoid streetscape bioretention basins and driveways. This
crossing is to be installed with TGIS’s in accordance with IPWEAQ RS-090 – 094 drawings. Please refer to
Barlow Shelley Drawing1856-R36 E.




                               Figure 5: Barlow Shelley Drawing 1856-R36 E

Item 14 – Driveways

There are still driveways shown on the operational works plans. Only show access driveways on
plans R35-R42 for lots referenced in conditions 8 and 19a. Remove all other driveways from those
plans (even those currently shown on those plans as future driveways – those indicative positions
may well change when future development applications for those lots are lodged).

Stockwell Response

Following discussions with Council’s traffic engineer, driveway crossovers for Lots 2 and 22 have been
removed. For reasons discussed, some future driveway locations are proposed to remain on the plan set to
avoid future damage of the streetscape by contractors for the proposed Lots during the subdivision
maintenance period, and informal establishment of access location around streetscape obstacles for these
lots.
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Item 16 – Sight Lines at the Emergency Access

Sight lines available at alternative locations have not been considered, nor have sight lines when
exiting from the central median of Walter Hay Drive. It is expected that a number of location options
would be assessed, with the location achieving the maximum balance of sight lines for crossing and
entering the Walter Hay Drive carriageways then being adopted, provided that location also meets
bushfire requirements

Stockwell Response

As discussed with Council’s traffic engineer, Condition 8 of the approval requires the emergency access
egress from proposed Lot 23 to be in the north-western section of the Walter Hay Drive frontage. Condition 50
a proposed that the egress point be located the southern point of Easement E on SP167978. Barlow Shelley
drawing 1856-R41 E confirms the driveway location is located at an appropriate distance from the intersection
to provide a suitable site distance.




                               Figure 6: Barlow Shelley drawing 1856-R41 E

There is 70m site distance in the southern direction along Walter Hay Drive from Lot 23, and 100m site
distance in the northern direction along Walter Hay Drive from the median access break. This is in accordance
with the minimum AUSTROADS guidelines for a 60km/hr design speed.

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Item 18 – Horizontal alignment of Hofmann Dr and Road C

There is no technical assessment included with the response in the Barlow Shelley letter of 16
October 2020. At the very least minimum horizontal curve radii and reverse curve requirements from
the relevant standards need to be identified, and justification then provided if those standards can’t be
met.

It is also noted that the existing horizontal curve in Hofmann Drive at its current eastern end, from
aerial photography appears to have a radius of approximately 100m. The existing end of the
constructed road appears to be at about CH200 on plan R37. However, the proposal is to commence
construction in Hofmann Drive at CH228.376, so to reconstruct the last 30m of the existing
construction in Hofmann Dr. The proposal is to reconstruct the existing R100 curve at the existing
end of Hofmann Dr, with a new R50 curve between CH217 and CH192, and then an immediate reverse
curve of R50 between CH192 and CH173.

A similar improvement to the reverse curve in Road C would also be appropriate.

Stockwell Response

Following discussions with Council’s traffic engineer the horizontal alignment has been amended. Improvements
to this section include the straightening of the footpaths; the removal of the reverse curve; and the flattening of the
horizontal radii to 100m in length. Please refer to Barlow Shelley drawing 1856-R37 E. This achieves compliance
with Austroads Guide to Road Design Part 3: Geometric Design.




                                 Figure 7: Barlow Shelley drawing 1856-R37 E
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  Stormwater

  General

i) The discharge of flows into the biopods is raised in a number of items below. Reference should be made
   to Section 3.4.2.2 of the Bioretention Technical Design Guidelines (Water by Design, 2012) for advice
   on addressing these issues
  Stockwell Response

  Inlet details have been provided on all bioretention and street tree device plans, to demonstrate inlet functions
  into the basins. Please refer to Barlow Shelley drawings 1856-SW19E – SW30E.
  Drawing SW19
i) Provide a section at the lowest point in the roadway adjacent to the biopod and show that the extended
   detention depth in the biopod will not pond into the kerb channel at that point.
  Stockwell Response
  The kerb lip levels for the lowest point in Road A along the line of the basin have been provided on the
  bioretention section and are also shown in the layout to show the position. This is consistent with the road design
  plans and demonstrates the extended detention does not pond past the kerb invert into the roadway.




                                  Figure 8: Barlow Shelley drawing 1856-SW19 E


ii) Provide details of how the cut-outs of the barrier kerb will be managed to avoid scour of the biopod
    batter.
  Stockwell Response

  Inlet details have been provided on all bioretention and street tree device plans, to demonstrate inlet functions
  into the basins. Please refer to Barlow Shelley drawings 1856-SW19E.
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   Drawing SW20, SW21, SW22

i) Section B - Is the footpath now partly below top of kerb? How does this work with interfacing with the
   rest of the verge profile for the remainder of the road? Are you proposing to set the footpath down
   locally adjacent to the biopod to minimize the batter? What does his mean in terms of frequency of
   inundation of the footpath at this location? For clarity, provide a dotted line showing the standard verge
   profile on this section.
   Stockwell Response
   The footpath has been raised so this would not result in a vertical step edge. As the streetscape bioretention
   basins have surface runoff enter from kerb and channel, they also surcharge at the kerb inlet level so there is
   little to no risk of footpath inundation from these devices. Please refer to Barlow Shelley drawing 1856-SW20 E
   Section B.




                              Figure 9: Barlow Shelley drawing 1856-SW20 E Section B
ii) The maximum batter angle is to be provided at the most upstream point of the biopod where the batter
    will be steepest.
   Stockwell Response
   The finished RLs have been provided at all ends of the narrow linear basins. All bioretention devices do not
   have a greater batter angle than 1:2. Please refer to Barlow Shelley drawings 1856-SW19E - SW26E.

iii) Inlet sections not consistent with Cross-sections
   Stockwell Response
   All inlet sections have been amended to show the sub-soils in the correct locations. The inlet section is to
   demonstrate the filter surface level relationship to the concrete pit lip in the treatment device.

iv) Update sections B, C, D to be taken at the location of the kerb “cut-out” (i.e.adjacent to the biopod)
   Stockwell Response
   The inlet cut-out has been positioned at the sag (lowest) for each treatment device. This is confirmed by cross
   reference the lip level at the road sag point from the road long sections with the inlet position on the bioretention
   layout plans. Please refer to 1856-SW19E, SW20E, SW21E, SW22E.
v) Provide details for the “400mm cutouts”. There are typical details for a kerb turnout, chute and forebay
   for biopods which can be found from other biopod projects undertaken on the Sunshine Coast. Provide
   calculations showing that 400mm is sufficient to convey the minor design flow or else widen to the
   required width.
   Stockwell Response
   Inlet details have been provided on all bioretention and street tree device plans to demonstrate the inlet function
   into the basins. Please refer to Barlow Shelley drawings 1856-SW19E - SW26E.
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 vi) Section D – what is the batter width behind BOK (face of kerb distance shown) and what is the batter
     angle? Why can’t this biopod be shifted closer to the RP boundary to facilitate a more suitable batter
     given there is no footpath in this verge?
    Stockwell Response
    This basin is now relocated behind the footpath alignment along Hofmann drive and within existing Covenant J.
    The basin position outside the infrastructure service corridors should be referenced from IPWEAQ RS-100 and
    101. Please refer to Barlow Shelley Drawing 1856-SW22E.


vii) Given the steepness and shortness of many of the batters behind back-of-kerb, how is it proposed that
     these batters will be able to be vegetated? It is suggested that a maximum batter of 1 in 2 and minimum
     batter length of 0.5m is required to establish batter planting successfully.
    Stockwell Response
    Batter lengths behind the back-of-kerb are kept at 0.5m long minimum to ensure suitable planting width is
    available for vegetation retention of the shorter slopes. All bioretention devices do not have a greater batter
    angle than 1:2. Please refer to Barlow Shelley drawings 1856-SW19E - SW26E.


viii) Why has Basin 4A now been added and what other alternatives are available? This basin connection
      will be prone to blockage and will in any case receive limited flow due to the piped connection to the
      kerb. It appears there are limited alternative connection options due to the lack of available fall and
      presence of the footpath. An alternative location or increased size of other devices should be
      investigated.
    Stockwell Response

    As discussed with Council’s stormwater engineer, there is insufficient depth to pipe the stormwater runoff
    from the southern side of Hofmann drive treatment device with a vertical filtering mechanism and then
    collect it at the outlet to discharge to surface. This is in line with our discussion and Council’s agreement.




                              Figure 10: Barlow Shelley drawing 1856-SW20 E Section B

    The stormwater access to this treatment device has been amended to provide sufficient room for a
    225mm high reinforced concrete box culvert under the pedestrian footpath to drain the kerb and channel
    to the treatment device.
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Page 10

   Drawing SW24D
i) Provide a detail for how the flows in the kerb in the driveway are discharged to the bioretention basins
   Stockwell Response
   A Type B1 kerb and channel is located around the full length of the downstream perimeter of the internal fire
   access / driveway pavement. Runoff is then discharged at each end of the basins. Please refer to Barlow Shelley
   drawing 1856-SW24 E.
ii) Section F shows the pit crest as being higher than the downslope bund height, meaning no flow will
    ever get into the pit. Amend and indicate minimum setdown of pit crest from edge of pavement
   Stockwell Response
   The bund height is 50mm higher than the pit crest allowing the overflow pits to receive runoff after the 200mm
   extended detention depth. Please refer to Barlow Shelley drawing 1856-SW24 E.
   Drawings SW25 and SW26

i) Standard drawing DS-077 is intended for small, discrete systems consisting of a single tree and being
   approximately 1m2 in size and grated. Those types of systems would typically be interspersed with
   standard street tree plantings. Local examples exist in Sippy Downs Town Centre. What has been
   proposed here is a biopod system with trees in it and they are no different to the other biopod systems
   proposed as part of this application and have the same functional issues. It is suggested that DS-077 is
   of limited applicability to the current proposal and the details of the open biopod systems for these
   drawings should be fully documented as for the other systems

ii) Provide a section behind the stormwater pit showing how the biopod interfaces with the pathway. It
    appears retaining will be required. If so, identify how safety will be addressed


   Stockwell Response

   Following discussion with Council’s stormwater engineer, street tree treatment devices have been remodelled
   and redrawn as bioretention devices. For clarity, we are no longer proposing to rely on DS-077 as a standard
   detail. These have been detailed with the same or similar outcome to the bioretention devices already shown,
   except for an overflow riser pit. The “Street Tree Basins” are proposed to fill the extended detention level to
   the kerb invert level at the basin inlet at which point the runoff will bypass the basins in the kerb and channel
   to the adjacent downstream kerb inlet pits. Filter levels and adjacent surface levels have been provided for
   these treatment devices as well. Please refer to Barlow Shelley drawings 1856-SW19E - SW26E.




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Page 11

Landscaping

i) The 10 wide revegetation for the Hofmann Drive frontages (required by Condition 53(a)) does not extend
across the full frontages for Lots 9 & 10 on the design plans.
Stockwell Response

Element Designs have provided updated landscaping plans to show 10m wide revegetation areas extended
across the full frontage of Lots 9 and 10.

 

   

  

PROPOSED BIO FILTRATION DEVICE
{EFER TO SHEET 20 FOR ADOMTIONAL
DETALS

    
   
 

10M WIDE REVEGETATION AREA
REFER TO SHEET 23 FOR
SPECIES UST

  
    
 

SELECT ROAD RESERVE
CLEARED AREA TO BE

 
  
 
 
 

PROPOSED BO FILTRATION DEVICE
REFER TO SHEET 20 FOR ADOTIONAL
Cerats

oS BUSTING CONCRETE
oe as, a ae
Neral bt

Figure 11: Element Design Drawing ED20265 OPW11-G

 

 

 

Mark, please do not hesitate to contact me directly if you have any queries relating to anything discussed in
this letter. Stockwell has engaged a local Sunshine Coast contractor who is ready to commence work on site
when the Operational Works approval is issued.

Yours Faithfully,

Z

Harry Hurst
Stockwell Development Group

  

CUBS,

Ce: Diago Carrico

Attachments:

° Attachment 1 — Updated Road Works Design prepared by Barlow Shelley — Rev. E dated 26.11.2020

e Attachment 2 — Updated Turning Path Plans prepared by Barlow Shelley — Rev B. dated 26.11.2020

e Attachment 3 —- Updated Stormwater Design Plans prepared by Barlow Shelley — Rev E. dated 26.11.2020
e Attachment 4 — Executed Covenant J Document

e Attachment 5 — Updated Landscape plans prepared by Element Design — Rev. G dated 26.11.2020

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DEVELOPMENT = FUNDSMANAGEMENT PROPERTY MANAGEMENT DESIGN & CONSTRUCTION