RFI - Attachment 3 - Stormwater Management Plan

Figure 3.2 – Adopted Surface Material for Each Area



Rainfall data for the locality was obtained from the Bureau of Meteorology IFD charts, with the temporal distribution
of rainfalls provided using the patterns obtained from the ARR Datahub. The rainfall intensities have been increased
by a factor of 1.2 to allow for climate change impacts projected to 2100 climate conditions. Refer to Appendix B -
DRAINS Modelling Results for details of the BoM and ARR data used in the modelling. Models were run for 1% and
10% AEP storm durations of 10 minutes to 720 minutes for the ensemble of ARR temporal patterns for each event.
Based on the estimate catchment time of concentration (approximately 45 minutes), the cut-off time for each
duration was extended by an hour to ensure the effects of temporal patterns was fully captured by the model.

The simulations were run for both the existing terrain and stormwater infrastructure, as well as the developed terrain
consisting of a proposed upgrade to Carpenters Road, upgraded culvert crossing and internal stormwater network.
The resultant depths, velocities, depth velocity products and surface height at each grid square within the active
extent of the modelled terrain were recorded for each storm event across all durations.

The resulting data for each storm was aggregated using asc_to_asc software to find the median storm event within
each duration, and then determine the maximum result of these medians across all durations with the critical result
obtained at each grid square. This data has been filtered to remove isolated grid squares and flowpaths and
drainage features disconnected from the subject channel for ease of review.

Due to the 5m grid spacing, it was noted that the grids did not necessarily align with table drains, culvert crossings
and the roadway as their widths are typically at or below the resolution of the model. To account for this a higher
resolution simulation using 1mx1m grid squares and 3 sub grid samples was run for each of the critical median storm
events identified at the culvert crossing to ensure the behaviour at this key area was accurately represented. Table
3.2 – Critical Median Storm Event at culvert crossing presents the storms that produced the maximum of median
results across all storm events which were modelled at 1m intervals.




Project number 21020                                                                                    Page 13 of 36
File RECOR Concept Stormwater Management Report - 21020.docx, 2022-09-05
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