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Response to RFI 30-03-22
Attached to the e-mail Further Advice response from Neil McKenzie & Assoc OPW21/0272.
Attached to the e-mail 0182 - Further Advice.eml, inside Response to Further Information Request OPW21/0272 - Unitywater letter - Correspondence from Neil McKenzie & Assoc. Re: Water Quality and Stormwater 1-6 items -32 Viewland Drive, Noosa Heads - email 1 of 2.
Suite 14, Clayfield Courtyard
699A Sandgate Road, Clayfield Qld 4011
Ph: 07 3862 1886 Fx: 07 3862 1397
E: [email protected]
March 30, 2022
Our Ref: 20-004
Noosa Council
P O box 141
TWEANTIN 4565
Re: OPW21/0272 MCU20/0128
Information Requested dated 11/01/2022
Further Advice
Water Quality & Stormwater
Item 1.
We have reviewed Council’s requirements for providing severe storms to 1:2000 year ARI as
well as 1% AEP at year 2100 including sever blockage. We feel this is unreasonable,
however, to satisfy Council’s request we have undertaken the following:
- Analysis has been undertaken for the 1:2000 year ARI storm. This is greater than the
1% AEP (at year 2100) and, therefore, should satisfy Council’s requirements.
- With respect to blockage we have incorporated 100% blockage on pits collecting
stormwater from surface landscaping and gardens. We have also provide for a major
blockage of the orifice which has been upgraded to 200mm diameter. We note that
QUDM specifies that blockages only need to be considered where suitable blockage
materials exist within the drainage catchment. This we consider as unlikely in this
development.
- The analysis was undertaken using Watercom’s latest design software “Drains”. We
have included the model for year 2100 stormwater event. The checking module, we
understand, is available to Council for checking purposes. Results of the requirement
for the much larger storm has resulted in the following modifications to our original
model.
a) Upgrade to a number of internal stormwater pipe sizes
b) Slightly modified unit floor levels
c) An overland flow path has been provided around apartment 1.
d) Raising of the bioretention basin wall height to 74.6m in lieu of 74.4m
e) Provision of a weir overflow in the retention tank as well as an increase in size.
Neil McKenzie& Associates | 20004 RFI OPW21/0272 1
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Item 2.
Analysis has been undertaken for the 1% AEP (2100) for the detention tank, biobasin 1 and
biobasin 2 with severe blockage. The bio basins are just starting to overflow but with
minimal discharge of 9 litres/second.
Item 3.
Detention tank and bio basin levels have been modified as necessary.
Item 4.
The drains model has been provided with the response for Council to check the calculations
and model assumptions. A hard copy of the data model output is also included.
Item 5.
The drainage model has been provided with this response. The program is available for
Council from Watercom to view the model to carry out their review. We have also provided
a hard copy of the model data and output.
Item 6.
(a) An overflow flow path has been incorporated into the stormwater infrastructure.
Blockage of any stormwater pits will allow the overland flow to discharge through
the carpark and into biobasin 2.
(b) Rock energy dissipaters have been included to the biobasins
(c) Retaining wall heights have had to be increased slightly due to Council’s
requirements for 1% AEP (year 2100) 1:2000 year ARI and severe blockage
modelling. We have no alternative with regards to altering these heights.
(d) Supporting calculations have been provided for a 20% increase in the 1% AEP
generally as requested. The swale drain easily carries the flow.
(e) Deluca will be providing the approval as requested
(f) End of swale calculations are provided as per item (d)
(g) Provided in drawings
(h) Provided in drawings
(i) Provided in drawings
(j) Provided in drawings
Attachements:
Swale Drain Calculations
Drains Model
Model Data Spreadsheet
Model Output Spreadsheet
Neil McKenzie& Associates | 20004 RFI OPW21/0272 2