Document 1 · OPW11/0177

It is proposed to link the RIP's together by a pair of 150mm dia slotted uPVC
balance pipes to prevent overtopping should one RIP become inoperable.




5.0    CALCULATIONS


In order to model the operation of the RIP's, a spreadsheet has been developed
and used for similar projects in Noosa Shire.

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 duration for a 10 year or 100 year average return interval
(ARI), depending on location of the RIP.

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 substorm with substorm 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 in Section 4. A factor of safety of 2.0 was applied to this infiltration
rate. Each RIP was then sized to prevent overtopping the appropriate design
storm event of any duration.

Spreadsheet model results are attached in Appendix C.




S3000/L5&6/11/SWMP- Stormwater Management Plan April 2011                 Page 2 of 2
SH/cf
                         Tate Professional Engineers Pty Ltd