Original source · versioned page text

Stormwater Management Plan (Quantity)

Attached to the e-mail Doonella Stage C (Email 6 of 7) Stormwater Management Plan - OPW14/0197.

Plans and drawings

This document appears to be plans or drawings. Its page text below holds only the words printed on the drawings, without the drawings themselves, so it may be jumbled or hard to follow. To see the plans as drawn, choose Original above or download the file (both need you to log in).

 

Our Ref: B09182.W.01.MS.ip.Authorities.docx
Contact: Andrew McPhail B - OW N
Smart Consulting

RPS Australia Asia Pacific

C/- Brown Consulting (QLD) Pty Ltd
PO Box 997

BUDDINA QLD 4575

17 April 2013
Attention: Sian Davis

Deat Sian,

Proposed Residential Development — Lake Doonella, Noosa Stage C
Stormwater Management Plan (Quantity)
Updated Management Strategy

Brown Consulting (QLD) Pty Ltd have previously prepared a Flood Investigation & Stormwater
Management Plan (Report No. B09182.W-02A dated October 2011) for Stockland Pty Ltd for the
proposed Stage C Residential Development at Lake Doonella, Noosa.

A hydrological analysis was previously undertaken to determine the change in peak flows from the
ptoposed Doonella Subdivision and the mitigation provided by the proposed stormwater detention
measures. Hydraulic modelling was also undertaken to determine post development flood levels to
confirm proposed lot and road levels had appropriate flood immunity along the environmental corridor
through the site.

Since the submission of this report, Sunshine Coast Regional Council (SCRC) has indicated that the use
of the environmental corridor for detention (referred to as the Dodonaea Close Detention Basin)
outlined in the Stormwater Management Plan was not acceptable. Subsequent meetings with SCRC
have led to the design change process. New peak flow management options have been proposed, with
Option 3 deemed to be viable. This was indicated in an email from Senior Development Planner
Dennis Wallace dated 30 March 2013 (refer to Attachment 1) in which it stated:

Of the SWM options submitted, only Option 3 was a presented as viable and doesn’t appear to provide significant
benefits over the original proposal in regard to soil hydrology and impacts of existing vegetation. On this basis, council
would be willing to amend the approval(s) to allow for the originally proposed Dodonaea detention area, provided we
can also do the following:

© = Allow for fauna passage, including a fauna underpass;

© Rehabilitate the fauna corridor area post construction disturbances and the changes to the soil hydrology

and vegetation that will result from the detention area;
© Obtain an Op Works revegetation/ rehabilitation approval for the above.

This letter report presents the analysis and results for the new peak flow management strategy
(Option 3) for the proposed residential subdivision as requested by Council. It is noted that post
construction rehabilitation of the environmental corridor is outside the scope of this letter.

Level 6, 199 Grey Street South Brisbane QLD 4101 Australia Brown Consulting (QLD) Pty Ltd 1
PO Box 10349 Adelaide Street Brisbane QLD 4000 Australia ABN 38 109 428 506
Telephone +61 7 3895 3444 Facsimile +61 7 3895 3400 brownconsulting.com.au

Stormwater Management Plan (Quantity).pdf · 4.5 MB (large file)

Large file: the download may take up to a minute.

Searchable page text hides email addresses. Original files are unchanged and may show email addresses.

Full text of the other 7 pages

Page 2

New Peak Flow Management Strategy (Option 3)

The Option 3 strategy to mitigated peak flow increase from the development involves incorporating
changes to the configuration of the previously proposed Twigrush and Dodonaca Basins, with two new
Detention Basins designated as Basins B1A and B1C.

Changes to the T'wigrush Basin and provision of two new basins allows for the reconfiguration of the
Dodonaea Basin outlet to incorporate a fauna crossing, with the objective to also reduce peak flood
levels and times of inundation within this basin.

The configuration of all the detention basins within the strategy to achieve the objectives is presented
in Table 1 below. Note that for Option 3 Sub Catchment 2B2 now bypasses the Twigrush Basin. Refer
to Drawing No. B09182.W-SK01B in Attachment 2 for the updated Stormwater Management
Catchment Plan.

Table 1: Option 3 Basin Configurations

a
Upstream Catchment BiA BIC C1,,C3, €2 aA, B1B
Storage Volume (m+) 1,080 1,100 1,210
Detention Depth (m) 1.5! 1.8! 2.1! -
chien Ae 9.3! 13! 7.6! 9
Basin Top RL (m. AHD) 10.8 14.8 9.7 12.25
Outlet Structure 1x 225 diaRCP | 1x 225diaRCP | 1x375mmdiaRCP | 1x 450mm dia RCP

1. A depth of 300mm is provided for bio-retention treatment below the detention bottom.

The previous Watershed Bounded Network Model (WBNM) for the site has been updated to
incorporate the Option 3 strategy. Assumptions and methodology are consistent with previous
investigations and analysis for the site. Details of the updated developed sub-catchment areas and
calculated fraction impervious values are presented in Table 2 below. Refer to Drawing
No. B09182.W-SK01 IssueB for the location and delineation of each sub catchment area.

Table 2: Developed Scenario Sub-Catchment Details

Level 6, 199 Grey Street South Brisbane QLD 4101 Australia
PO Box 10349 Adelaide Street Brisbane QLD 4000 Australia
Telephone +61 7 3895 3444 Facsimile +61 7 3895 3400

Brown Consulting (QLD) Pty Ltd
ABN 38 109 428 506
brownconsulting.com.au

Page 3

Results

The results of the analysis indicate that the new and reconfigured detention basins and outlet structures
achieve the non-worsening objective. There is now a decrease in peak flows for an 100 Year ARI event
of 5%. Peak flow results are shown in Table 3 below.

Table 3: Existing and Mitigated (Option 3) Peak Flows

The Water Surface Levels (WSL’s) for each basin have also been considered (refer to Table 4 below).
Basin B1A, B1C and the Twigrush Basin are consistent with freeboard requirements. Depth of flow
across the overflow weirs are also less than 300mm during the Peak 100 year ARI event.

Table 4: Option 3 Basin WSL’s

For the Dodonaea Basin results indicate that there is a dectease in peak WSL’s compared to that
specified in the previous report. Results are presented in the Table 4 above. Significant reductions in
the detention volume and the WSL between the previous strategy and Option 3 have been provided.
The resulting changes in volume in the Dodonaea basin are presented in Table 5 below.

Table 5: Dodonaea Basin Ch: in Volume

480 50 -430
950 170 -780
1,300 270 -1,030

1,810 430 -1,380
2,070 620 -1,450
100 830 -1,380

The peak 100 year ARI WSL in the Dodonaea Basin (11.21m. AHD) will also ensure the fauna passage
will remain flood free during this event. A reduction in the time for the basin to drain has also been
demonstrated. It takes Dodonaea Basin 30 minutes less to empty during a 100 year ARI event then
previously determined.

Level 6, 199 Grey Street South Brisbane QLD 4101 Australia Brown Consulting (QLD) Pty Ltd 3
PO Box 10349 Adelaide Street Brisbane QLD 4000 Australia ABN 38 109 428 506
Telephone +61 7 3895 3444 Facsimile +61 7 3895 3400 brownconsulting.com.au

Page 4

The times for Dodonaea Basin to empty for different ARI events are present in Table 6 below.

Table 6: Dodonaea Basin Em Time

120 120 0
165 140 -25

175 140

185 140 -45

195 140 55
100 175 145 -30

In summary the Option 3 strategy incorporating new Basins B1A, B1C and the reconfiguration of the
Twigrush and Dodonaea Basins will still mitigate peak flow increases from the proposed development.
The reduction in WSL’s in the Dodonaea Basin compated to the previous sttategy is significant. ‘The
time in which the Dodonaea Basin takes to empty has also reduced.

The peak flow management strategy has been updated to achieve non-worsening objectives while the
Dodonaea Basin configuration allows for the installation of a fauna crossing under Dodonaea Close.
We trust this information is acceptable and respectfully request the new stormwater management
strategy for Lake Doonella, Noosa Stage C Development be approved.

Should you require any further information, please do not hesitate to contact Andrew McPhail ot the
undersigned on.
(07) 3895 3444.

Yours sincerely,
Brown Consulting (QLD) Pty Ltd

Ss \
Andrew McPhail
Principal Engineer — Water and Environment

ATTACHMENTS
1. Email from SCRC Senior Development Planner Dennis Wallace

2. Drawings
Level 6, 199 Grey Street South Brisbane QLD 4101 Australia Brown Consulting (QLD) Pty Ltd 4
PO Box 10349 Adelaide Street Brisbane QLD 4000 Australia ABN 38 109 428 506

Telephone +61 7 3895 3444 Facsimile +61 7 3895 3400 brownconsulting.com.au

Page 5

ee ee ee,
BROWN

Smart Consulting

 

ATTACHMENT 1: SCRC Email

Level 6, 199 Grey Street South Brisbane QLD 4101 Australia Brown Consulting (QLD) Pty Ltd 3
PO Box 10349 Adelaide Street Brisbane QLD 4000 Australia ABN 38 109 428 506
Telephone +61 7 3895 3444 Facsimile +61 7 3895 3400 brownconsulting.com.au

Page 6

From: Denis Wallace [mailto:[email protected]]
Sent: Wednesday, 20 March 2013 12:21 PM
To: Sian Davis
Cc: Kerri Coyle; Conor Neville; Mark Lewis; Leon Rowlands; Rob Sewell
Subject: RE: Doonella - Stormwater Dicussion

Sian,

I’ve been able to get internal feedback on the material you’ve provided, which may allow us to
proceed with the change process.

Of the SWM options you’ve submitted, only Option 3 was presented as viable and doesn’t appear to
provide significant benefits over the original proposal in regard to soil hydrology and impacts on
existing vegetation. On this basis, council would be willing to amend the approval(s) to allow for the
originally proposed Dodonaea detention area, provided we can also do the following:

    -   Allow for fauna passage, including a fauna underpass;
    -   Rehabilitate the fauna corridor area post construction in relation to the construction
        disturbances and the changes to the soil hydrology and vegetation that will result from the
        detention area;
    -   Obtain an Op Works revegetation / rehabilitation approval for the above.

I assume you would be agreeable to this option but let me know if you have any concerns or if there
are aspects I haven’t addressed.

Regards

Denis Wallace | Senior Development Planner
Regional Strategy & Planning I Planning Assessment - North
Sunshine Coast Council

Phone: 07 54495179
Email: [email protected]
Website: www.sunshinecoast.qld.gov.au
Mail:    Locked Bag 72 Sunshine Coast Mail Centre Qld 4560

Page 7

ee ee eee
BROWN

Smart Consulting

ATTACHMENT 2: Drawings

Level 6, 199 Grey Street South Brisbane QLD 4101 Australia Brown Consulting (QLD) Pty Ltd 6
PO Box 10349 Adelaide Street Brisbane QLD 4000 Australia ABN 38 109 428 506
Telephone +61 7 3895 3444 Facsimile +61 7 3895 3400 brownconsulting.com.au

Page 8

 

 

NOOSAVILLE
PRIMARY SCHOOL RS

fs/ | (BIC S BZ oo aa! ab CSS

   

 

 

 

 

 

4 “DODONAEA \

 

§ as | | | | site ‘DISCHARGE LOCATION
-7 is SS EXISTING CATCHMENT PLAN
-” 1S! — SCALE: 1:2000(A1)
- — =! - SS . : - SCALE: 1:4000(A3)
7
/ 2 *
< J B25)
So .
7 = e, — Sy . & = SEA-EaGie — Z
/ LOCATION A ‘ BE YY At , S . Sy (
| ey, SS és y nS
/ AL co pooonnea BASIN < Ct 3 rs ~
"Op \ sy ' . \
/ LOCATION-B GT 7 E \
/ @ KON i ¥
| iS! ry
y s
! "hi ia si Fe
\ TWIGRUSH BASIN

/ BIA % ve 3 mony NN

2A) “py
/ BASIN out are DISCHARGE ,LOCATION “op

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
   

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q e f
LOCATION C
D1 ®
\ hy LOCATION D LEGEND
4
\ a @7 - /
&’ SITE BOUNDARY
\ - ~ - /4] 7 CONTOURS
/ / a
\ | / / EXISTING CATCHMENT BOUNDARY
/ \ PED CATCHMEN
| FS / BECKMANS ——_— = DEVELOPED CATCHMENT BOUNDARY
\ | GREEN SUBDIVISION e FLOW LOCATIONS FOR
HYDRAULIC MODELLING
\ So FLOW DIRECTION
\ XN J
\ \ y | |_| JA | NOTES:
aE
1. THIS DRAWING IS TO BE READ IN CONCEPT PLAN ONLY
N = — — SWANBOURNE WAY ‘ \ “ === | CONJUNCTION WITH BROWN CONSULTING LETTER NOT TO BE USED FOR
Ls sasuon-stoveg, DATE 1-0-292 THE: 088 ( | NO. B09182.W.01.MS.ip.Authorities. CONSTRUCTION PURPOSES
Xref's: X_BO09182.W_TITLE X_B09182.W_BASE X NO9004 BASE_XTRACT_130416 USR: Tin Stewart
par [ones [nn] ON SORES TORT he STENT DRAWS TE
AMENOMENT DETAILS DESIGN CHEGK SURVEYOR: PMM Sunshine Coast Pty Ltd re
ee 7 INNOVATION PARKWAY KAWANA WATERS BROWN CONSULTING (QLD) PTY LTD ‘CONSULT AUSTRALIA
Blab [ws | 1.0.0 | waren ro LETTE sore Wath paves DATED APA 78 14000 10 oy 20s) soso at Ph (07) 5436 7888 Fax (07) 5493 6630 | ~— Di STORMWATER CATCHMENT PLAN
gle prawn cneox| °2200 ss PROWECT We APPROVED vanes cr xa ons [FLOOD INVESTIGATION FOR SUBDIVISION Brown Const (QD) Ply Lit ats
NE B09182.W BRENT TMAS RPE 1862 AT LOT 800 ON SP 153455 Smart WN ee Goes a ner eee, Gampay | Pan Homer TSB
sir FOR & ON BEHALF OF BROWN CONSULTING {QLD} PTY LTD BECKMANS ROAD, NOOSAVILLE Bice Gators Mons fy Bape ttwtoat LC dOBL B09182.W-SKO1 B

Sign in to NoosaWatch

Stormwater Management Plan (Quantity)

See the original

The supporting record

Source document

My Comparisons