Site Based Stormwater Managment Plan

                                                                                         20169 - SBSMP/2
                                                                                                     Page 10




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        0.086      0.103      0.157       0.195        0.234        0.298        0.341
  Pre development B         0.073      0.087      0.132       0.162        0.193        0.243        0.278
  Post development B        0.100      0.120      0.183       0.226        0.271        0.345        0.398
  Pre development C         0.024      0.028      0.043       0.053        0.063        0.079        0.090
  Post development C        0.011      0.013      0.020       0.025        0.030        0.037        0.040


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 two on-site detention (OSD) systems 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, and Lot 79 on SP138388, northeast 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 Building 1 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 Buildings 5-8 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.
    3. Runoff from the roof catchment of Buildings 2-4 will flow via downpipes an internal
       drainage system, where it will be directed to the detention basin located at the northeast
       corner of the site prior to discharge to the Lawful Point of Discharge within Lot 79 on
       SP138388.




Site Based Stormwater Management Plan
Proposed Townhouse Development at 99, 101 & 105 Eumundi Noosa Road, Noosaville