Attachment 4a - Engineering Report Part 1 · MCU18/0015

   7.2.1        Peak Discharge Calculations


   Refer to Engineering Drawing C5756/15/P34, attached as Appendix C for details of
   external catchments.


   Due to the location of the site at the lower end of a larger catchment, the Time of
   Concentration (TOC) is governed by sheet and channel flow over the upper reaches of the
   catchment. The TOC will therefore be similar for the existing and developed scenarios.
   Development works over the site will result in minor increases to impervious areas within
   the total contributing catchment. The following catchment characteristics should also be
   considered;


           -   The minor external catchment to the west is fully urbanised (60% Impervious).
           -   The major external catchment to the south and east is generally undeveloped
               parkland (Yunaman Bushland Reserve and Noosa National Park) with minor
               urbanisation (Peppers Resort). This catchment is unlikely to be modified.
           -   Development works over the subject site are considered a ‘one-off’ modification
               to the catchment.


   Refer to Table 7.2.1a for a summary of Rational Method calculations for the subject site
   and external contributing catchments. Refer to Appendix E for detailed Time of
   Concentration and Rational Method Calculations.


   Table 7.2.1a Rational Method – Pre Vs Post Developed
                      Area         Fi   TOC       C10      Cy       Iy       Q -1% AEP     Pre Vs Post
                       (Ha)     (%)     (min)                      (mm)        (m³/s)       Variance
Existing              30.44    15.0     19.0    0.730    0.876     196         14.52            -
Developed             30.44    16.0     19.0    0.732    0.878     196         14.56         +0.3%




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