C2. Eng Report

                                                     Proposed Service Station – 175 Eumundi Noosa Road, Noosaville
                                                                                  Ref: 20769 C R001 Rev 06 09.02.17
                                                                                                     February 2018


         Q = (2.78 x10-3) Cy Iy A                                                                   Equation 1


          Q = Peak flow rate (m 3/s) for average recurrence interval

          Cy = Co-efficient of runoff for ARI of y years (dimensionless)

          A = Catchment area (ha)

          Iy = Average rainfall intensity (mm/hr) for a design duration of t hours and an ARI of y years


8.2.3   Catchment Area (A)

         Catchment areas were measured using AutoCAD, contour surface data and known cadastral
         boundaries. Catchment boundaries and areas for both the pre-developed and post-developed
         scenarios can be seen in Appendix A and Appendix C respectively.

8.2.4   Co-efficient of runoff (C)

         Given the 1I10 for Noosaville of 72.31 mm/hr and the relevant impervious fractions for each catchment,
         Tables 4.5.3 and 4.5.4 of QUDM 2013 were used to determine the C10 values for the pre-developed
         and post-developed scenarios. From the C10 values the remaining coefficients of runoff were derived
         for all storm events up to and including the 1% AEP (100 year ARI) using the frequency factors
         presented within Table 4.5.2 of QUDM 2013. Please refer to Appendix F for more details.

8.2.5   Time of Concentration

         The time of concentration (tc) for each catchment was calculated using a combination of sheet flow
         (using the Friend’s equation – Equation 4.5 of QUDM 2013), channel flow (using figure 4.8 of QUDM
         2013) and standard inlet times (using table 4.6.2 of QUDM 2013). Please refer to Appendix F for
         more details.

8.3      External Catchment
         No significant upstream catchments act on the proposed site.

8.4      Pre-Development Hydrology
         The hydrology of the pre-developed catchment has been assessed in accordance with Section 4.0
         of QUDM 2013 using the Rational Method. From QUDM Section 4.0, the theoretical calculated peak
         discharge for storm events ranging from the 63.4% AEP (1 year ARI) to the 1% AEP event (100 year
         ARI) has been calculated and a summary of the results is presented in Appendix F.

         The subject site has a total area of 1,972m2 and currently is comprised of a single lot featuring
         detached commercial dwellings. The site area is comprised predominantly of impervious areas made
         up of roof and driveway land uses. The Coefficient of discharge (C10) value for the site was derived
         from QUDM 2013 Table 4.5.3 and Table 4.5.4. Fy frequency factors were applied to determine runoff
         coefficients for various average recurrence interval (ARI) storm events in accordance with QUDM
         2013 Table 4.5.2.

         QUDM 2013 Section 4.6 was applied to determine a total time of concentration (TC). Due to the
         existing catchment (EX1) consisting of smaller sub-catchments having short lengths of travel and the
         site being in a developed urban nature, ADG has adopted a 5-minute time of concentration (Tc) for
         the existing catchment. Rational Method calculations were performed, the results of which can be
         seen outlined in Error! Reference source not found..

         Please refer to Appendix F for a summary of the Rational Method calculations and all parameters
         used.


BRISBANE / SYDNEY / MELBOURNE / GOLD COAST / SUNSHINE COAST / DARWIN / PERTH                               Page 16