Attachment 4 - Stormwater Managment Plan

SQIDEP Evaluation                                                    SPEL Basin, Sippy Downs


Checks were carried out to examine the historical rainfall record (historic radar) and a
number of selected events as a ‘sensibility check’ to verify the on-site measurements were in
line with what should be expected.

Events

Radar records were used to examine historic rainfall. This is able to provide an indication of
rainfall occurrence and intensity. Figure 4 shows radar results for the 7th July and the
corresponding flow rates provided in ‘SQIDEP BOE Application - Supporting Information’.

In general terms:

    •   Higher rainfall intensities should manifest as higher peak flows through the device:
    •   Flow peaks through the device should match altered intensity as a storm front
        passes; and
    •   The duration of an event (from start to finish) should match the radar record.




Figure 4 Radar Rainfall Checks

For the majority of events provided for analysis the observations indicate a reasonable
match in storm and flow peaks between the site recordings and meteorological results, with
two exceptions for the 8th July 2017 and 23 September 2017.

Both these days report relatively low flow through the device (i.e. less than 0.5l/s) and
reported rainfall depth for these events were 5.4 mm and 6.6 mm respectively. Scrutiny of
the flow rainfall depth for other days indicates a higher order of flow response. As such, it is
possible that the characterization of the storm event is incorrect and has been plotted
incorrectly. Given the overwhelming correlation of the other events to the data, the rainfall
and event data is generally accepted.

Note that it is possible that the sample collected on the 8th July was as a result of continuing
flow generated by the event on the 7th July, however the radar record does not appear to
indicate that there was sufficient rainfall on the 23rd September to generate the tabled data.


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