Development Application part 7 of 10 Stormwater Management Report - MCU13/0092

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3.      Site Hydrology

3.1 Method and Approach


The stormwater discharges from this site were calculated using the rational method. This method as described in the
Queensland Urban Drainage Manual (QUDM)is commonly used in municipal hydrology and is more than adequate
for the design requirements. The Rational Method is based around the Rational formula:



Q=-
      C/lyA
y
  360



Where:              Qy     =   Peak flow rate (m3/s)for the average recurrence interval (ARI)of y years

                    Cy     =   Coefficient of runoff for ARI of y years

                    A      =   Area of catchment (ha)
                   t
                       I   =
                               Average rainfall intensity (mmlhr)for design duration of t hours and
                       y

                               an ARI of y years.



When designing the stormwater drainage system the following points have been considered:


Storm water treatment shall be designed for a 3 month storm event, calculated as Q1 x 0.5; and Stormwater
reticulation is to cater for Q3 month, Q20 and Q100 storm events.


For the purposes of this stormwater quality assessment, the area of the proposed development requiring stormwater
quality treatment has been divided up into 1 catchment:

Table 1 details catchment names, areas and storm event flows for the catchment based on the Rational Formula.
Refer to Appendix B for details of catchment calculations and Appendix A, drawing 13-024-C34, for catchment areas.


                                               Table 1: Catchment and Flow



Catchment                  Catchment Area            Ql00 Major Flow      Q20 Minor Flow         Q3 month Treatable Flow
Catchment E                     0.1743 ha               0.153 m3/s            0.111 m3/s                 0.021 m3/s




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