RFI - ATTACHMENT A - SBSMP - Rev 2

                                                                                           20169 - SBSMP/2
                                                                                                        Page 9




5.1.5 Peak Flows
Refer to Table 5-3 for a summary of the predicted minor and major discharge rates for pre and
post development conditions and Appendix E for the Rational Method calculations.

                              Table 5-3 – Pre and Post Development Peak Flows

    Property State        Q1 (m3/s) Q2 (m3/s) Q5 (m3/s)     Q10 (m3/s)     Q20 (m3/s)   Q50 (m3/s)   Q100 (m3/s)

  Pre development A        0.048       0.057      0.086       0.107          0.127        0.162        0.186
  Post development A       0.077       0.093      0.141       0.175          0.210        0.268        0.306
  Pre development B        0.027       0.032      0.049       0.061          0.072        0.091        0.105
  Post development B       0.028       0.033      0.050       0.062          0.075        0.095        0.110
  Pre development C        0.022       0.026      0.040       0.049          0.058        0.073        0.084
  Post development C       0.020       0.024      0.036       0.045          0.054        0.066        0.073


The proposed development will result in an increase in impervious surface areas and will
consequently increase stormwater runoff peak flow rates in Catchments A and B.

Hence, it is proposed to utilise an on-site detention (OSD) system to mitigate the stormwater
runoff of the proposed development prior to discharging to the existing stormwater infrastructure
within Lot 46 and 62 on SP132578, southeast of the site.

Catchment C will result in a decrease in stormwater runoff peak flow rates. Therefore, no
detention is required to mitigate Catchment C. However, a rainwater reuse tank has been
proposed which will provide some mitigation.

Refer to Section 5.3 for the XPSTORM Modelling analysis of the site, Appendix E for the Stormwater
Quantity Calculations, Appendix F for the Concept Site Levels and Drainage Plan and Section 6 for
the Stormwater Quality Management Plan.

5.2 Proposed Drainage Patterns
The proposed drainage patterns are as follows (Refer to Appendix F):

Roof Catchment:
    1. Runoff from the roof catchment of Townhouse Units 1-8 will flow via downpipes to a
       rainwater tank located at the northwest corner of the site for rainwater reuse with
       overflow discharging to the Lawful Point of Discharge within the Eumundi Noosa Road kerb
       and channel.
    2. Runoff from the roof catchment of the rest of the site will flow via downpipes an internal
       drainage system, where it will be directed to the detention basin located at the southeast
       corner of the site prior to discharge to the Lawful Point of Discharge within Lot 46 and 62
       on SP132578.
Ground Catchment:
    1. Surface runoff from the ground level hardstand and landscaping areas will be collected by
       various stormwater pits connected to the internal drainage network, where it will be
       directed to the detention basin located at the southeast corner of the site prior to
       discharge to the Lawful Point of Discharge within Lot 46 and 62 on SP132578.

Refer to Appendix F for the Concept Site Levels and Drainage Plan.


Site Based Stormwater Management Plan
Proposed Townhouse Development at 101-105 Eumundi Noosa Road, Noosaville