2 Emerald SWMP 2213_Rev1

                                                                          Callaghan & Toth


4.       STORMWATER DESIGN AND ASSESSMENT


4.1      Proposed On-Site Stormwater Treatment Process

The developed site was divided into Sub-Catchments as shown on Figure 1.1 and the
detention system is listed below:

1. An Underground Rainwater Detention Tank will be required to collect water from all the
   roof area and carpark of the commercial building. A total of one (1) tank 8.73m long with
   a capacity of 7.4m3 will be provided for the new commercial building. The tank
   discharge to an overflow pipe discharging to the underground drainage system. The total
   tank capacity is to be 7,400 litres and is adequate for the approximate attenuation of
   runoff back to predevelopment concentrations for AEP1%, 10%, 50%.
2. The underground drainage system is designed to convey a 20% AEP event. An overland
   flow path has been provided to convey large events.



4.1.1 Rainfall Data
The meteorological data used for the BOM IFD table for Cooroy 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 tanks.

The underground rainwater detention tanks adopted have 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 Emerald Street is not to be affected by this
development, there will be no change to the capacity of drainage to Emerald Street.




Hafner                           2213 SWMP_Rev1.docx                          July 2022   8
2213