124-002 Technical Memorandum Revision B

The existing house on the property will be demolished as part of the new construction. The existing house has
a footprint of 336m2. This is a coverage of 48% of the overall 690m2 site area. Currently this roof area is
connected to rainwater storage tanks with their outlets discharging overland towards the eastern boundary.
There have been some crude attempts at fashioning drains along the rear boundary to help channel these
flows away from the existing buildings and towards the drainage outlet.

The proposed new dwelling will have a proposed area of 344m2 which is 50% of the site area. It is expected as
part of the building design, a majority of this roof area will be able to be discharged to Enterprise Street.
Nevertheless, there will still be a portion of stormwater that will need to be managed in order to remove any
nuisance flows towards the east.




                   PROPOSED STORMWATER MANAGEMENT

It is proposed that the downstream drainage system remains untouched. It is unknown if any other properties
are connected to it and the area over the pipe alignment appears to be well established.

It is instead proposed to remove all but necessary flows from entering this existing system. By installing tanks
at the rear of the property would allow capture of peak flows as well as provide retention storage for water
re-use. Once the tanks are filled, the roof catchments would then be diverted to the Enterprise Street frontage.

Based on the existing dwelling roof area of 336m2 the flows from the existing roof to the eastern boundary
would be 24L/s approximately based on a Q20 5-minute storm.

The tanks are expected to be incorporated into the retaining along the eastern boundary. This would ensure
that they would not be obtrusive.

It is expected that the tank could be either cast in-situ concrete as part of the building construction or placed
as a proprietary product. The tank is shown as part of Figure 2 and would allow connection from the proposed
roof area.

Areas of the proposed dwelling that are too low to be connected to the tanks such as outside impervious areas
would divert to the eastern boundary. Calculations provided by the Hydraulic Engineers indicate that these
flows would be at a maximum of 22L/s. This is less than the calculated volume currently reaching the eastern
boundary and ensure a non-worsening condition. These flows would be discharged onto the property site and
dispersed through gravel beds for scour protection.



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   2261 david low way, peregian beach, qld 4573      acn: 626 671 092            [email protected]