2576 - SBSMP-01 (Feb 2026)

4.3       WBNM Hydrologic Model

A lumped parameter hydrological model was developed to simulate the rainfall-runoff
response for pre-development and post-development scenarios. Rainfall losses due to
infiltration were taken from the ARR Data Hub provisions for the catchment location. A stream
lag factor of 0.5 was applied for artificial channels and 1.0 for natural channels.


                                       Initial Losses (mm) Continuing Losses (mm/h)
               Pervious (ARR Data Hub)           32                   2.6
               Impervious                        0                     0
                        Table 4-1 ARR2016 Initial and continuing losses from the ARR Data Hub



The pre-development and post-development catchments are shown in the tables below. Catchment 1 encompasses the entire
                               site. Refer to Figure 2-2 Pre-development catchment plan

Figure 2-3 for the post-development catchment plan.


                                                Area (m²) % Imperv
                                    Catchment 1  18403       0%
                                   Table 4-2 Pre-development catchment parameters

                                                       Area (m²) % Imperv
                                    Catchment 1         18054      86%
                                    Catchment 2           349     100%
                                    Total               18403      86%
                                  Table 4-3 Post-development catchment parameters



The proposed stormwater system generally functions as follows:
          Runoff from roof areas will collect in gutters, which is conveyed through the pipe
           network to the stormwater basin. The paved areas are shaped to direct flows
           southward to the stormwater basin.
          In a storm exceeding the primary event, the overland flow paths have sufficient
           capacity to convey the flows to the basin, where it is discharged via the spillway. The
           discharge point of the basin is to be directed into the stormwater reserve. The
           catchment at the northeast side unable to be graded toward LPOD1 runs eastward to
           LPOD2 toward Taylor Court.




2576-SBSMP-01_Version 1.0 (February 2026)                                                              Page 16 of 23
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