Stormwater Management Plan -OPW (A) · OPW25/0042

   •    Size RIPs/RICs and surrounding bio basins such that all flows up to
        100-year ARI are infiltrated on site

   •    Test RIP/RIC sizes derived above via a Quantitative MUSIC model to
        predict performance of RIPs/RIC and quantify percentage of incident
        rainfall infiltrated on site.



This approach satisfies both performance criteria of Council Condition 46 (f).

Infiltration of 100-year ARI catchment flows is a higher standard than the 10
year ARI required by EMP 1 or Council Condition 46 (f) and is consistent with
the approach taken on previous Settlers Cove projects.

Quantitative MUSIC modelling employs infiltration rates of 3,600mm/hour
(1mm/second) as recommended in the MUSICX1.0 modelling guidelines for
coarse sands.



7.1 RIP/RIC CAPACITY MODELLING- EXCEL SPREADSHEET

In order to model the operation of the RIP’s, a spreadsheet has been
developed and utilised for all previous stages of Settlers Cove.

Temporal patterns for Zone 3 from the Australian Rainfall and Runoff,
Volume 2 were applied. These temporal patterns were used in conjunction
with the average rainfall intensities for the Noosa region to create a series of
design storms of varying durations and for a range of different average return
intervals (ARI). Notably existing observed and documented rainfall intensities
from AR&R were increased by 20% as per Council ‘Climate Change’
requirements.

Temporal patterns were converted to flow rates by breaking each storm event
into a series of short duration storms. A triangular flow verses time
approximation was used for each sub storm with sub storm flows then added
to produce flow Vs time for RIP inflow.

Outflow and water depth were then calculated through iterations for the
duration of the storm based on the infiltration rate / head relationship
discussed above. A factor of safety of 2.0 was applied to the observed
prototype infiltration rate. Each RIP/RIC was then sized to prevent
overtopping in a 10-year ARI storm event of any duration, with 100-year ARI
storms contained within the RIP/RIC and adjacent bioretention basin.
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A6769/25/SWMP/Rev OpW(A) – Feb 2025
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SH/PL
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