Attach G- Engineering Report

                                                                                                                 ENG
                                                     Engineering Report & Stormwater Management Plan
                                             Date:          5/02/2016      Document No.:     15087-ENG-01.Docx

                                              By:              MRS          Revision No.:              A


Appendix G - Stormwater Pipe and Gully Calculations

The proposed building is to be constructed over the existing overland flow path. It is therefore
proposed that the stormwater captured in Garnet Street is conveyed to Wimmer’s Lane via a pipe
with a Q100 capacity.


The proposed upstream site stormwater catchment calculated from Department of
Infrastructure, Local Government and Planning (DGILP) SPP Interactive Mapping as 3.1ha. Refer
to Figure 1 below.




                             Figure 1 Upstream site stormwater catchment


 The Q100 flow associated with this catchment with a time of concentration calculated as 13
 minutes is 1886l/s (Refer to attached calculation spreadsheet).


Based on the upstream flow of 1886l/s, it is proposed to reroute a 750dia pipe, of 2100l/s
capacity, around the basement of the proposed development between Garnet Street and
Wimmer’s Lane. This capacity was calculated using a 1:33 slope (3600mm fall over 120m length
of pipe) and the catchment area and IFD rainfall data shown in the attached spreadsheet.


The existing pipe connected to the gully pit in front of the site is of 525dia and with a capacity of
1176l/s. This results in an excess flow of (1886-1176) 710l/s which will occur as overland flow in
Garnet Street and needs to be picked up in the sag gully.




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