The development works must be designed and constructed generally in accordance with the plans and reports submitted with the development application:
Civil Engineering Report Version 4 Dated 22 October 2018 prepared by Northrop (specifically, the dam storage volumes, outlet structures and modelling results presented in this report).
TUFLOW models prepared by Northrop (specifically, all versions and scenarios, including the normal and dam break scenarios, up to and including the additional modelling data relating to the revised single duration event re-runs submitted on 9 November 2018).
Dam Break Assessment Version 2 Dated 22 October 2018 prepared by Northrop
Blockage Strategy Dated 22 October 2018 prepared by Northrop
Sensitivity Analysis Dated 22 October 2018 prepared by Northrop
Civil Engineering Package (Plans) Version 5 Dated 19 October 2018 prepared by Northrop
The following amendments and additional requirements also apply to the design and construction of the development works:
Basin Set-out/ Flow Configuration
a) The conversion of the eight temporary sediment basins, one adjacent to the western basin, three around the main lake, two within the southern basin and two along the creek corridor south of Red Gables Road to raingardens will eventually be required. The flow configuration to and from all basins needs to be finalised in consultation with, and is subject to the written approval of, Council’s Principal Coordinator – Stormwater and Waterways.
b) Concern remains over the level of maintenance and cost of maintenance of the main lake, particularly considering the proposed pumping of the lake for eight hours each day at 500 litres per second.
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PAGE 86 c) Alternative options needs to be considered and reported upon in relation to lake treatment/ recirculation. Mechanically pumping stormwater from the main lake to nearby basins is not accepted with the information provided currently.
d) A report on the management and maintenance costs of the considered options is required.
e) An operation maintenance spreadsheet is provided as Appendix E of the Civil Engineering Report. Once a preferred option is agreed to by Council’s Principal Coordinator – Stormwater and Waterways an asset management plan in accordance with IPWEA NAMS.PLUS3 Asset Management guidelines is required.
f) Main lake seepage is included in the submitted water balance calculations. If the lake is to be lined, confirmation is required as to whether the seepage calculation has considered it is not permeable.
g) Pumping is indicated in the Civil Engineering Report to cease in the northern basins during and after rain events but makes no mention of the same applying for the southern basins.
h) The saturation of the raingardens is a concern. Consideration needs to be given to having wetlands or sand filters instead.
Gross Pollutant Traps
a) Gross pollutant traps are to be provided at locations required by Council. Raingarden/
basin/ lake inlets from collector roads and/ or the town centre are to have gross pollutant traps installed with suitable all weather maintenance access:
b) Gross pollutant trap maintenance access cannot be conducted from the carriageway of the adjoining road. Suitable driveway access off a road with a concrete maintenance pad alongside or immediately adjacent any planned gross pollutant trap is required.
c) Any maintenance access pad/ area are to be located at a distance from the gross pollutant trap that allows the required vehicles, apparatus and machinery to reach the device and manoeuvre as required.
d) Pedestrian footpaths may be temporarily closed for gross pollutant trap maintenance but ideally should be able to remain open at all times. The design needs to consider this intent for each instance.
e) The temporary closure of a lane of traffic will not be accepted for gross pollutant trap maintenance.
f) Street trees or landscaping are not to be located where it may hinder maintenance access or any maintenance activity.
Water Quality Elements
a) The detailed design of all proposed raingardens must include cross sections that identify bed levels, surface levels and the lake standing water level to ensure appropriate levels are achieved for the raingardens to drain whilst maintaining suitable depths of filter media and drainage materials. The typical section included on Sheet DA11C is not sufficient for this purpose. The same comment applies to Section 1 on DA020. The bulk earthworks design must be amended to comply with this requirement so as to avoid any potential design conflict or compromises in design at a later date.
b) Raingardens/ bio-filtration basins should be designed and constructed to drain dry.
Outlet pipes from a raingarden/ bio-filtration basin should be located above the two year ARI level of the receiving waterway.
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PAGE 87 c) Raingardens must be designed and constructed in accordance with the latest version of
Adoption Guidelines for Stormwater Biofiltration Systems, CRC Water Sensitive Cities.
d) Wetlands should be designed and constructed in accordance with the latest version of The Constructed Wetlands Manual, Department of Land and Water Conservation NSW.
e) Provision of shallow water zones around the perimeter of the lake planned to be planted out with macrophytes are not identified on the plans. This detail must be included with the detailed design of the main lake and its embellishment.
f) The Civil Engineering Report makes mention of facility maintenance and water quality monitoring by Council. More detail is to be provided in relation to the maintenance and monitoring required.
Civil Engineering Package (Plans)
a) The basin/ raingarden maintenance access ramps include grades up to 20% which must be reduced to 12.5% (maximum).
b) Basin spillways must not overtop a footpath or cycleway. If the conflict cannot be designed out through the location and configuration of the cycleway or basins, these crossings must be bridged instead.
c) Rock walls are not to have blank terminals. Both upstream and downstream terminals are to be keyed back into the embankment at 45 degrees.
d) Sheet DA001 has notes for “rainwater reuse” which are not relevant to these works.
e) Sheet DA001 refers to hydromulch under “landscaping” for temporary stabilisation.
Hydromulch is not to be used in riparian areas.
f) Sheet DA01A includes notes for “bio-retention swales and basin” which needs to be considered in conjunction with the above listed matters. If wetlands are proposed additional detail will need to be added for those.
g) Sheet DA01A under “scour protection rock” needs to be looked at with respect to the minimum layer depth; 150mm versus 75mm.
h) A note should be added to ensure rock scour protection is to finish flush with the adjoining ground surface level.
i) Sheet DA003, the rock armouring at the two basin inlets and one basin outlet (Chadwick Drive) needs to be extended below the standing water level. It finishes part way up the slope/ batter currently.
j) The notes/ detail showing the “existing overland flow path” and “temporary channel to be utilised until upstream lot is developed” needs to be better detailed/ explained on Sheet DA003. The same applies to the scour protection within the channel itself on the western site boundary.
k) The planned finish/ surface treatment of Swale 01 need to be confirmed. The inlet/
connection to Sediment Basin C1/ H1 at the end of this swale need to be detailed also.
Refer to the section that stops/ drops off on Sheet DA011.
l) Sheet DA006 needs to be amended to extend the long-section for Channel 01 further into the lake, not dissimilar to what is shown for Channel 02 on Sheet DA008.
m) Sheet DA008 is missing a note relating to a drop structure at chainage 874 along Channel 02.
n) Sheet DA011 shows the basin/ raingarden maintenance access ramps with grades that are too steep.
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PAGE 88 o) Sheet DA014 needs to be amended to better detail the transition from Channel 02 to the
inlet headwall.
p) Sheet DA017 Section 2 needs to be realigned to dissect Raingarden 01 rather than sit in the embankment on the southern edge of this raingarden.
q) Sheet DA029 needs to be amended to include the detail of the rock armouring in Section A. On the upstream/ lake side the rock armouring needs to be extended past the standing water level and keyed in (similar to the downstream side). On either side the rockwork needs to finish flush with the adjacent surface level. The scour protection in Section B needs to be extended beyond the crest on both side and the riprap scour protection rock sizing of D50 = 200mm needs to be verified/ appears too small. The rockwork sits above the footpath based on Section C and needs to be amended so they are level.
r) Sheet DA29A needs to extend Section A to the lake, and include a second cross section through the rockwork where the current long-section section stops.
s) Sheet DA035 includes a “typical creek section” that has a note referring to jute matting.
The matting is likely to roll if not overlapped and well pinned or replaced with mesh as has been used previously. With respect to the “typical sandstone steps detail” on the same drawing, the closest rock to the lake edge needs to be buried below the standing water level. A smaller row of rocks or other edge treatment along the base is required.
Civil Engineering Report
a) Page 18, Table 4 – Detail drawings missing (as below).
b) Page 18, Table 4 – Red Gables Road Bridge (which also has hydraulic influence on the design of the lake) to be included in this table.
c) Page 20, last paragraph and Page 21, Figure 4 – Rewording of Title (ARR 2016 hazards categories).
d) Page 48, second last paragraph – Rewording required, “zero blockage and design blockage respectively for existing structures entering and exiting”.
e) Page 49, last paragraph – This does not apply to all the farm dams within the Precinct.
f) Figure 4 - Needs to be updated to show the blockage factors applied in the model/
blockage codes for each culvert, as well as a table describing what each code means and the blockage percentage for each design event to be added. Call out boxes to be used for bridges.
g) Figure D4 – Spell out ‘0b’.
Dam Break Assessment
a) Figure 4 – Needs to be updated (as above).
b) Pages 14 and 15, Tables 6 to 8 – Exact locations are to be shown on a plan (similar to Figure A0 of the Civil Engineering Report) by using points and coordinates.
TUFLOW Model/s
a) The revised TUFLOW models submitted to support the design considered only a single duration 1% AEP event for the dam intact and dam break scenarios. All duration/ events/
scenarios are to be re-run with the new parameters and resubmitted in support of the detailed design. A complete set of modelling input and output data (revised runs using the correct inputs) is be submitted for review and written approval by Council’s Principal Coordinator – Stormwater and Waterways prior to a Construction Certificate being issued.
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PAGE 89 b) No changes in water levels at the lake and at any other areas except at the immediate upstream and downstream extents of the Maguires Road culverts are expected from the revised model run. This requirement applies to all duration/ events/ scenarios.
c) In resubmitting the TUFLOW modelling (as above) the information provided and how it is provided/ presented needs to comply with the requirements of Council’s Principal Coordinator – Stormwater and Waterways. Specifically:
d) GIS and TUFLOW files need to be presented in a format acceptable to Council.
Submission guidelines will need to be developed in consultation with Council staff to assist.
e) Any changes in modelling approach need to be clearly documented (for example, the use of a blockage matrix).
f) Each model submission will need two sets of TUFLOW control files, one with complete history of all versions and scenarios, and one simpler clean-up version related specifically to the current submission.
g) “Readme” files will need to be provided in addition to log files on scenarios and versions.
These files must include details of any new additions and approaches as well any relevent background information, source etc;
h) CSV files corresponding to point PO files contain same ID for duplicate points (the point IDs are not unique) and will need to be rectified with the resubmission.
i) Line and point PO files need to be updated in consultation with Council’s Stormwater and Waterways team prior to rerunning the model.
j) The design of some of the hydraulic structures included in the model is outside of the scope of this consent/ subject to separate development applications. The data used in the model must match the design detail to be provided:
k) The two Precinct D Boundary Road culverts (BdyCulV9a and BdyCulV9b). These need to consider the design of the works in that precinct specifically (subject to a separate development application) along with the eventual planned upgrade of Boundary Road and the development of the upstream Vineyard catchment on the opposite side of Boundary Road.
l) The Precinct D Valletta Drive culverts.
m) The Town Centre (Fontana Drive) bridge. The bridge modelled is relatively unconstrained and so even though that bridge will be designed and submitted later in a future package, the modelling being done now that informs the lake fixes the span, flood heights etc;
n) The Red Gables Road bridge. Unlike the Town Centre (Fontana Drive) bridge, Red Gables Road and the crossing at this location exists now. The model relies on this constraint being removed and replaced with a relatively unconstrained creek channel/
bridge crossing. The existing temporary basin south of Red Gables Road cannot be removed until this crossing is in place, as conditioned separately. The bridge modelled is relatively unconstrained and so even though that bridge will be designed and submitted later in a future package, the modelling being done now that informs the lake fixes the span, flood heights etc;
o) The invert level/s of the Maguires Road culverts need to be included.
p) Main Lake Bridge – Layered Flow Constriction Shape Point attributes need to represent the guidelines in TUFLOW Manual 2017 (details in Tables 6 to 22, Pages 6 to 86) so that a consistent approach is used in bridge modelling for all crossings.
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PAGE 90 Blockage Strategy
a) Page 4, second last paragraph – Remove “approximately”. Also in the same paragraph qualify the statement with further clarification, such as stating that the downstream impacts with respect to this sensitivity analysis is the difference in flood levels are between the ultimate developed case with zero blockage and the existing case with zero blockage.
b) Page 5, Table 7 – Change in wording by using “Design Scour Protection, Downstream Impacts, and Sensitivity Analysis” instead of “Design Scour Protection, Downstream Sensitivity Analysis”.
Sensitivity Analysis
a) Page 8, PMP Spatial Patterns – Sketch showing the spatial distribution depths need to be included.
b) Page 8, Table 5 – Shows 113mm for Ellipse C; should be 116mm based on the calculations.
c) Page 11, Paragraph 4 – Need to clarify why the 360 minute ellipse depths were applied (i.e. the derivation of the 540 minute storm was proven not to be critical and the assessment is redundant however was included in the assessment anyway to prove that it was not critical).
d) Page 17, first paragraph – Need to add text on why a smaller breach wedge was considered.
e) Page 19, last paragraph – Reference to figure numbers is necessary.
f) Figure A1A – Increase in lake water levels are expected. Further explanation is required in this regard.
g) Figures A3 and A5 – Increase in lake water levels need to be explained.