stormwater mgJ00300R1V1_25_Kauri_St_Cooroy_Complete · MCU18/0165

25 Kauri St Cooroy




4        STORMWATER QUANTITY
Hydrologic modelling of site stormwater runoff has been undertaken to size detention storage
that is able to mitigate peak site runoff to levels that are less than or equal to the existing
scenario.

Analysis has been undertaken for the 50%, 10% and 100% Annual Exceedance Probability (AEP)
events. The following scenarios have been investigated:

         1.          Base Case (Existing Site)
         2.          Un-Mitigated Developed Case (no detention)
         3.          Mitigated Developed Case (with detention)

Modelling has been carried out in accordance with ARR 2016 procedures using WBNM software
in conjunction with Storm Injector software.

4.1      Base Case
Hydrologic modelling of the catchment has been carried out using WBNM software developed
jointly by the University of Wollongong, Rienco Consulting and Balance R & D.

A WBNM model has been setup representing the site in its existing condition. The base case
model has a single sub-catchment representing the full site with zero impervious area.

A WBNM lag parameter of 1.3 has been applied. This value was selected by calibrating to the
QUDM Rational Method for un-mitigated developed site flows (refer section 4-3).

Modelling has been carried out for the full range of standard design event storm durations
ranging from 5 minutes up to 3 hours. For each duration, an ensemble of 10 different temporal
patterns has been modelled and the adopted peak flow is taken as the value closes to the mean,
with a bias to values above the mean (Storm Injector bias factor of 2).

Rainfall loss rates adopted for this investigation are based on values from the ARR data hub and
are shown on Table 4-1 and 4-2.

Table 4-1 WBNM Rainfall Loss Rates

 Pervious Area             Pervious Area    Impervious Area       Impervious Area
    Initial Loss            Continuing         Initial Loss         Continuing
       (mm)                Loss (mm/hr)           (mm)             Loss (mm/hr)

       Varies
                                2.6                 0                   0
  (see table 5-3)




J00300R1V1                                                                                   4