Stormwater Management Report · MCU19/0008

Refer to Table 1 and Appendix B for further details of the proposed system.
Table 1 - Detention system details

                        Description                                                  Value

 Tank Model                                                              20 x Atlantis Flo-Tank - Triple

 Gross Volume (m3)                                                                    7.32

 Detention Capacity (m3)                                                              6.96

 Dimensions (m)                                                           4.08(L) x 1.37(W) x 1.31(H)

 Infiltration Rate (m/d)                                                              0.6

 Catchment Area to Tank (Ha)                                                         0.040

 Catchment Area Bypassing Tank (Ha)                                                  0.021


3. 3       Hyd ro l o g i c an d Hyd rau l i c Mod el l i ng

The hydraulic and hydrologic modelling software package XPSTORM was used to model the pre-
developed and post-developed flow conditions for the site. XPSTORM provides a simulation of the
natural runoff processes and the hydraulic performance of stormwater infrastructure. An integrated
1D/2D hydraulic model was developed incorporating the TUFLOW engine. The TUFLOW engine
accurately represents site specific topography, defining flow paths, discharge, storage, and variation in
flow direction in addition to modelling flood hazard.
Hydrologic Modelling

The 0.5EY, 10% AEP and 1% AEP events were modelled. A number of storm durations including the
10 minute, 25 minute, and 1 hour duration were simulated for each return period for the pre-developed
and post-developed model.
Rainfall data was obtained from the ARR 2016 data hub. The ensemble of storms for each duration
was simulated for the pre-developed model and the median storm for each duration & ARI was
determined utilising the ensemble statistics utility. The resultant storms were utilised as the design
storms for each EY/AEP for both the pre and post developed models. The Laurenson method was
utilised to calculate runoff hydrographs with the following losses:
           Pervious areas – initial and continuing losses of 10mm and 2.6mm respectively. The value for
            initial loss has been reduced from the AR&R Data Hub value and is considered conservative
            given the existing soil conditions.
           Impervious areas – initial and continuing losses of 2mm and 0mm respectively
Hydraulic Modelling

An integrated 1D/2D model was developed to simulate the hydraulics of the stormwater drainage
network. The 1D network was limited to modelling the infiltration/detention tank in the post developed
model. Physical parameters for the storage node were calculated based on data obtained from the
manufacturer. The following parameters were utilised in developing the 2D network:
           A 0.5m grid cell size was utilised.
           The DTM was derived from LiDAR data obtained from DNRM




4 April 2019                                Stormwater Management Report                                   6
S18-030                                           22 Arakoon Crescent,