MOD 2 - Eastern Creek Retail Centre Stage 1

TG: 2018-561

RE: Eastern Creek Business Hub (SSD 5175 MOD 4 and SSD 8588 MOD 2) -
Rooty Hill Road South, Eastern Creek


Thank you for referring the abovementioned Modification to TransGrid
for review.

Please be advised after reviewing the proposal, TransGrid has no
objections to the proposed modifications as it does not affect
TransGrid's infrastructure

A Land status investigation on Eastern Creek Business Hub (SSD 5175 MOD 4
and SSD 8588 MOD 2) - Rooty Hill Road South, Eastern Creek, shows that
there is no Crown land features Exist.

Therefore, No comments Crown land at this moment.

Thank you.

I've had a look at the documentation as well as the Heritage Division's
earlier comments on these proposals, there are no State Heritage
concerns regarding the proposed modifications that require a formal
response from the Heritage Division.

See attachment

With regard to the above MOD 4, our Drainage Engineer has reviewed the
drainage submission by Henry and Hymas and identified substantial
problems with the drainage plans. It is not possible to provide
conditions to resolve these issues, and amended plans are required.
This review focuses on the basin layout and MUSIC modelling, and
amended plans are required which address the following:

SOUTH BASIN

1. On drawing 17D83_S96_C251 (02) the Water Quality Plan for pad 1
refers to primary treatment by either Enviropod or GPT. This option is
not acceptable as Enviropods do not treat oils or hydrocarbons. . This
is done only in the GPT. Plus the Enviropods in the carpark will not
generally treat roof flows and will make the MUSIC model invalid so
the CDS GPT is required. Amend note.
2. The GPT is required to treat approximately the 6 month flow. Based
on a catchment of 3.869 Ha this equates to a 6 month flow of about 344
l/s. The Rocla CDS 1518 is required to treat this flow. The CDS 1009
is unacceptable.
3. The strategy for pad 1 is to convey the 100 year flows to the basin
via the pipe system alone. The proposed 3 x 525 mm pipes at 0.5% to
drain the 100 year flows from pad 1 to the detention basin appears
undersized. (approximate capacity = 0.95 m3/s). Based on a catchment
of 3.869 Ha this equates to a 100 year flow of at least 1.4 m3/s.
Estimate that 3 x 600 mm pipes at 0.5% is required as a minimum.
4. On drawing 17D83_S96_C220 (02) Line N amend longsection based on
point 3 above including flows. The HGL is to refer to the 100 year
HGL. Review the HGL based on the 2.9 m long weir at pit N2 the depth
of 100 year flow over the weir is near 450 mm deep.
5. In reviewing the pdf document "Off take pit South" used to size the
twin 300 mm pipes to the bioretention the incorrect values for Ho and
Hu have been used. Based on a weir level of 40.25 Ho is 0.284 (invert
N-2 is 39.966) and Hu is 1.05 based on an overflow water level of
40.25 and pipe invert of 39.20. Check sizes and amend document.
6. Review the HGL losses in the bioretention system including the pipe
losses, pit losses including losses in the upflow pits as the level of
the weir at 40 25 cannot overcome the losses based on a TWL of the
bioretention of 40.15 plus a depth of overflow of at least a 0.1m i.e.
40.25. ie. There is no head in the weir level at 40.25 to drive the
design flow through the system against a head of 40.25. To assist the
filter media level could be lowered by 150 mm.
7. On drawing 17D83_S96_C240 (02) the layout of the bioretention
overflow pits are based on Detail 13 of Council's WSUD drawings. This
layout is based on a stand-alone bioretention basin design and not as
part of an OSD system. As proposed this arrangement creates
substantial bypass causing the OSD to become ineffective. Only the
underdrain subsoil line flows are to go direct to the outflow
headwall. Where this is part of an OSD basin these three pits are to
have sealed lids and a flat weir overflow provided across the 4 m wide
maintenance path set at the basin edge to the 300 mm bioretention
extended detention level with reverse crossfall directed to the OSD
basin (possibly near the scour protection for the pipe outlet).
Provide scour protection and a concrete seepage barrier across the
weir overflow or build this in concrete. Check weir width to limit
depth to 0.1 m maximum.
8. On drawing 17D83_S96_C240 (02) the outlet from the OSD is shown as
600 mm pipe at 0.5% and the 100 year outflow from drawing
17D83_S96_C241 (02) details a 100 year orifice discharge of 842 l/s.
It is good practise to design the outlet pipe from the orifice for
about twice the orifice flow or at least substantially more than the
orifice flow itself. The 600 mm pipe @ 0.5% conveys about 460 l/s and
is substantially undersized. Increase the pipe size accordingly.
9. On drawing 17D83_S96_C240 (02)
a) reduce in size the pipeline from the bioretention to the headwall
as only conveying underdrain flows.
b) provide a cut off wall through the rock weir overflow for the OSD
basin.
c) Refer to the 2 pipes within the bioretention basin as 300 mm
permeable pipes laid flat
d) The berm width around he OSD should be increased to a minimum of 2
m based on Council experience and the 1.2 m if used should be
justified by a geotechnical engineer. Set top of berm to a minimum of
39.40 to match the 300 freeboard shown on the northern basin.
e) On Section A the top of OSD berm is to be 39.40 minimum to give at
least 300 freeboard.
10. On drawing 17D83_S96_C241 (02) at the Discharge Control Pit
a) the pits should have surcharge style grates.
b) Provide a minimum 375 mm pipe from the small orifice to the larger
pit.
c) Increase the width of the 1.5 year orifice pit as it is too small
to contain the minimum 1.13 m2 Weldlok screen (20 x orifice area).
d) Detail how the 4.9 m2 Weldlok screen in the 100 year orifice pit
can be contained and accessed in a pit with 3 x 1200 x 1200 grates.
e) Show the new outlet pipe size from the 100 year control pit
11. On drawing 17D83_S96_C241 (02)
a) At the bioretention System Inlet Pit amend the invert of the 300 mm
permeable pipes to 39.15.
b) At the bioretention System Inlet Pit show the concrete top of pit
as 200 mm above the apron level.
c) Provide a detail of the weir overflow across the access track.
d) Show the 3 pits at "Outlet for large Bioretention System" with
sealed lids


NORTH BASIN
12. On drawing 17D83_S96_C251 (02) the Water Quality Plan for pads 2,
3 and 4 refers to primary treatment by either Enviropod or GPT. This
option is not acceptable as Enviropods do not treat oils or
hydrocarbons. This is done only in the GPT. Plus the Enviropods in the
carpark will not generally treat roof flows and will make the MUSIC
model invalid so the CDS GPT is required for each pad. Amend note.
13. The GPTs are required to treat approximately the 6 month flow.
a) Pad 2 based on a catchment of 4.063 Ha this equates to a 6 month
flow of about 361 l/s. The Rocla CDS 1518 is required to treat this
flow. The CDS 1009 is unacceptable.
b) Pad 3 based on a catchment of 2.244 Ha this equates to a 6 month
flow of about 199 l/s. The Rocla CDS 1015 is required to treat this
flow. The CDS 1009 is unacceptable.
c) Pad 4 based on a catchment of 4.110 Ha this equates to a 6 month
flow of about 365 l/s. The Rocla CDS 1518 is required to treat this
flow. The CDS 1009 is unacceptable.
14. The strategy for pad 2, 3, 4 and remaining upstream catchments is
to convey the 100 year flows to the basin via the open channel system.
The proposed 5 m wide appears slightly too small allowing for manning
n of 0.08 (little to low maintenance) and should be at least 6 m wide
and provide some freeboard. The crest width needs to be a minimum of
1.2 m throughout, preferably more to provide stability once
overtopped. The 0.3 m crest width is totally unacceptable.
15. On drawing 17D83_S96_C230 (02) a 300 mm bund is proposed to divert
870 l/s (shown as 870m/s) to the bioretention. There is no section
provide but (for a 6 m base width) estimating a diversion channel base
width of 1.2 m and a 300 mm high mound at 1V : 4H batters and a 1.2 m
crest width with n = 0.08 then Q = 172 l/s (Mannings Equation) << 870
l/s. The design of the diversion weir does not work. In addition the
EDD of the bioretention is 39.10 and allowing 0.1 m overflow the
backwater level is 39.20, however the plan shows a top of diversion
weir as 38.85 near the inlet pit < 39.20. Consequently the proposed
strategy here is compromised. The long lateral weir does not appear to
work in this circumstance. A more conventional weir set at say 45
degrees to the flow across a widened section of channel may give a
better outcome. The weir needs to be in concrete or otherwise
protected from scour. The channel needs to be widened and weir length
extended so that the total 100 year peak unrestricted flow can overtop
the weir without overtopping the crest (Including freeboard). Provide
calculations.
16. The current proposal to try and adapt the Council WSUD drawings to
suit the open channel is problematic. There will be substantial losses
in water entering the collection pits in the channel and discharging
to the bioretention, pipe losses, pit losses including losses in the
bioretention and particularly in the upflow pits, all to try and
overcome a backwater level of 39.20. If this is continued with then an
HGL check needs to be to undertaken to ensure that it actually works.
In addition the diversion inlet pits and pipe system needs to be
extended further upstream before the weir begins. The weir needs to be
sufficiently higher. To assist the filter media level could be lowered
by 200 mm.

Alternatively consider the following to minimise the head loss through
the bioretention. Provide through the embankment from the channel a
shallow box culvert sized to convey the 870 l/s to the bioretention
with the invert at the bio set to the filter media level. At the
outlet to the bioretention provide a very large concrete silt trap say
600 mmm deep and wider than the culvert as part of the scour
protection. Delete the bioretention internal pipes and upflow pits.
Provide from the silt trap two concrete flow spreaders each say 900 mm
wide around both sides of the basin and meeting at the other end to
ensure flows can be equally distributed throughout the basin. The base
area of the basin is to allow for the design filter area (900 m2) plus
area of flow spreaders and pits.
17. On drawing 17D83_S96_C230 (02) the layout of the bioretention
overflow pits are based on Detail 13 of Council's WSUD drawings. This
layout is based on a stand-alone bioretention basin design and not as
part of an OSD system. As proposed this arrangement creates
substantial bypass causing the OSD to become ineffective. Only the
underdrain subsoil line flows are to go direct to the outflow
headwall. Where this is part of an OSD basin these three pits are to
have sealed lids and a flat weir overflow provided across the 4 m wide
maintenance path set at the basin edge to the 300 mm bioretention
extended detention level with reverse crossfall directed to the OSD
basin (possibly near the scour protection for the pipe outlet).
Provide scour protection and a concrete seepage barrier across the
weir overflow or build this in concrete.
18. On drawing 17D83_S96_C230 (02) the twin outlets from the OSD are
900 mm pipe at 0.41% and the 100 year outflow from drawing
17D83_S96_C231 (02) details a 100 year orifice discharge of 1,424 l/s
for each pipe. Pipe nomographs indicates that the pipe capacity cannot
achieve this flow rate. It is good practise to design the outlet pipe
from the orifice for about twice the orifice flow or at least
substantially more than the orifice flow. Increase the pipe size
accordingly.
19. On drawing 17D83_S96_C230 (02)
a) reduce in size the pipeline from the bioretention to the headwall
as only conveying underdrain flows.
b) provide a cut off wall through the rock weir overflow for the OSD
basin.
c) Refer to the 2 pipes within the bioretention basin as 300 mm
permeable pipes laid flat where this system is retained.
d) The berm width around he OSD should be increased to a minimum of 2
m based on Council experience and the 1.2 m if used should be
justified by a geotechnical engineer.
e) On Section B the top of OSD berm is to be 39.25 minimum.
20. On drawing 17D83_S96_C231 (02) at the Discharge Control Pit
a) the pits should have surcharge style grates.
b) Review pipe size from the small orifice to the larger pit.
c) Increase the width of the 1.5 year orifice pit as it is too small
to contain the Weldlok screen based on 20 x orifice area.
d) Detail how the 18 m2 Weldlok screen in the 100 year orifice pit can
be contained and accessed in the proposed pit.
e) Show the new outlet pipe size from the 100 year control pit.
21. On drawing 17D83_S96_C231 (02)
a) At the bioretention System Inlet Pit amend the invert of the 300 mm
permeable pipes to 38.10 (if still applicable).
b) At the bioretention System Inlet Pit show the concrete top of pit
as 200 mm above the apron level (if still applicable)..
c) Provide a detail of the weir overflow across the access track.
d) Show the 3 pits at "Outlet for large Bioretention System" with
sealed lids
22. A vehicular access track (maximum grade 10%) needs to be provided
for both the southern and northern basins to enable vehicles to reach
both the bioretention basin and into the detention basin for
maintenance and exit in a forward direction.

Note: The above items were emailed to the Applicant's engineer (Thomas
Dempsey, Henry and Hymas) on 18 January 2019.

The Applicant is also requested to verify that their amended
submission (including MUSIC modelling) takes into account the
provision of a child care centre in Lot 2 which is intended to form
future SSD 5175 MOD 6.

I have also advised our Traffic Officer of the above requirements.
Should further concerns be raised in light of the above, I will also
notify you.

Please be advised that the above affects the engineering matters for
the Concept plan and detailed DAs and their modification applications
on the site, being assessed by myself (SSD 5175 MOD 4 and SSD 8588 MOD
2 Stage 1) and Kelly Coyne (SSD 5175 MOD 5 and SSD 8858 for Stage 2).

Letter uploaded

See attachments

See attachment

See attachment

See attachment

See attachment

See attachment

See attachment

See attachment