Attachment 2 - Stormwater Management Plan · 131998.981126.5

                                                                              Callaghan & Toth


4.     STORMWATER DESIGN AND ASSESSMENT


4.1    Proposed On-Site Stormwater Treatment Process

The developed site was divided into a Sub-Catchment to show the proposed areas for
detention as shown on Figure 1.1 and the detention system is listed below:

1. Above ground rainwater tanks will be required to collect water for stormwater detention
   purposes from the shed roof area. A total of two (2) 5,000L tanks (1.8m diameter x
   2.32m high manufactured dimensions) will be provided for the new shed. The tanks will
   discharge through a 40mm diameter orifice at a height of 0.83m above the invert of the
   tank and a 150mm diameter overflow pipe at the top of the tank. The depth below the
   orifice outlet will be used for toilet reuse. The total combined tank capacity is to be 7,000
   litres and is adequate for the approximate attenuation of runoff back to pre-development
   concentrations for AEP1%, 10%, 50%. See Figure 4.2 on page 9 for a detail of the
   proposed rainwater tank setup.
2. The underground drainage system is designed to convey a 20% AEP event for both the
   new shed/hardstand area as well as the new entry foyer/barbeque area. An overland
   flow path has been provided to convey larger events.



4.1.1 Rainfall Data
The meteorological data used for the BOM IFD table for Noosaville was used for the runoff
calculations



4.2    HYDROLOGY

The site has been modelled using HydroCAD 10 to determine the detention capabilities of the
rainwater tank.

The aboveground rainwater tank adopted has been sized so that runoff concentrations are
reduced back to predevelopment levels as shown in our calculations in Appendix 1.

As the existing runoff and catchment extents to Satinwood St is not to be affected by this
development, there will be no change to the capacity of drainage to Satinwood St and the
Lake Doonella Bushland Reserve outlet.




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