Site Based Stormwater Management Plan

5. WATER QUANTITY


Stormwater from this site has been calculated using the Rational Method as described in the
Queensland Urban Drainage Manual (QUDM) except as amended. The Rational Method is the
most commonly used method for drainage design in Queensland and uses the Rational
Formula:

       Qy = Cy . tIy . A /360

       where

       Qy = peak flow rate (m3/s) for average recurrence interval (ARI) of ‘y’ years
       Cy = coefficient of discharge (dimensionless) for ARI of ‘y’ years
       A = area of catchment (ha)
       tI = average rainfall intensity (mm/h) for a design duration of ‘t’ hours
         y
            and an ARI of ‘y’ years.

The ARI is defined as the average or expected values of the period between exceedances of a
given discharge. The ARI for the design storm for both the major and minor system depends on
the current and potential land use, convenience and safety for pedestrians and vehicular traffic.

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

   •   Stormwater treatment shall be designed for a 3 month storm event
   •   Stormwater reticulation is to cater for Q10 (.11% EY) and Q100 (1%EY) events




NMA-SBSWMR-20004 Noosa Youngcare                                                                7