20220089 Jirrima Cr SWMP

     2.2. Existing Drainage Patterns
Surface runoff from the existing site occurs as overland sheet flow following the natural surface contours which
typically drain towards an existing drainage feature that traverses the site approximately 200m from the site frontage.
This watercourse flows from south to north as indicated by the yellow dotted line within Figure 2.2 – Existing Site
Drainage Characteristics (Queensland Globe Watercourse Identification Map, 2022) continuing through Lot 11 SP
335366 to the north.
The upstream catchment contributing to the existing watercourse through the site have been identified by the blue
polygon on Figure 2.2. This catchment measures approximately 0.65km² in area extending to the south and east of
the subject site.

The upstream catchments are concentrated at the existing culvert crossing in Jirrima Crescent approximately 200m
south of the existing site, made up of 2 1800x900 box culverts beneath the road. Based on discussions with Council,
the immunity of this crossing will govern the required level of immunity for the driveway access within the subject
site. Council flood modelling data has been obtained for this culvert which found it was immune from flooding up
to the 50% AEP storm event but remained trafficable for both the 10% and 1% AEP storms. Refer to Appendix B
Council Flood Modelling Results for the data obtained from Council for the upstream culvert. This stormwater culvert
as identified from Council mapping is indicated by the green line in Figure 2.2.
Downstream of the proposed development the stormwater flows traverse the adjacent properties before joining an
unnamed tributary of Ringtail Creek for approximately 2.3km before it eventually connects into Ringtail Creek and
continues to the north (refer Figure 2.2).




Project number 20220089                                                                                  Page 6 of 23
File 20220089 Jirrima Cr SWMP.docx, 2023-05-09 Revision 0


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