Att 1 - Engineering - RFI Reponse · MCU21/0117.01

                                                                                       23098 - SBSMP/4
                                                                                               Page 10




5.3.1 Hydraulic Model Parameters
The following parameters were obtained from the ARR DataHUB and have been adopted as part of
the DRAINS IL-CL hydrological modelling:

    1. Impervious area initial loss (mm): 0mm

    2. Impervious area continuing loss (mm/hr): 0mm

    3. Pervious area initial loss (mm): 32mm

    4. Pervious area continuing loss (mm/hr): 2.6mm

5.3.2 Design Storms
As defined in the NSC City Plan Policies and QUDM, the following design storms were adopted:

    1. Minor Drainage System: 10 year ARI statistical flood (Q10 storm);

    2. Major Drainage System: 100 year ARI statistical flood (Q100 storm).

5.3.3 Intensity Frequency Distribution
The BOM data and temporal patterns have been used for the DRAINS modelling and were obtained
for the following coordinates:

    1. Latitude: -26.4181

    2. Longitude: 152.9128

Refer to Appendix G for a copy of the BOM IFD data table.

5.3.4 Pre-Development Model
The pre-development catchment model utilises the following values in Table 5-4. The sub
catchment area taken into account for the pre-development catchment is 0.2275ha. Refer to
Figure 5.1 below for a screenshot of the pre-development model.

               Table 5-4 – Pre-Development Catchment Characteristics for Catchment
                                                                            Remaining
                                              Effective Impervious Area                     Pervious Area
         IL-CL Hydrological Model                                         Impervious Area
                                                         (EIA)                                  (PA)
                                                                               (RIA)
                    Percentage of area (%)                 0                     8               92
Pre-Development
   Catchment         Time of Concentration
                             (mins)
                                                           5                     2               9.7




                                    Figure 5.1 – Pre-Development Model

Site Based Stormwater Management Plan
Proposed Townhouse Development at 5 Pearl Street, Cooroy