Attachment 4a - Engineering Report Part 1 · MCU18/0015

Proposed development works over the site will result in minor increases (0.3%) to peak
discharge within the existing flow path. An impact assessment is provided below in order
to quantify the effect of this minor increase to stormwater discharge on flow depths
within the existing flow path, immediately downstream of the subject site.



7.2.2   Overland Flow Path Depth Analysis


Refer to Engineering Drawing C5756/15/P34 attached as Appendix C for details of the
existing flow path that traverses the site. The Manning’s Equation has been used to
determine the maximum channel flow depth under existing and developed conditions.


The overland flow path profile is well defined and has been plotted from detailed survey.
Under existing conditions, a maximum flow depth of 1.422m (1% AEP) is noted within the
channel, directly adjacent the northern property boundary.


Proposed development works over the site will result in minor increases to peak discharge
and consequently, a minor increase to maximum flow depths with the existing flow path.
Under developed conditions, a maximum flow depth of 1.423m (1mm increase) is noted
within the channel during the 1% AEP storm event.


This minor increase to flow depth will not cause an actionable nuisance to downstream
properties.




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