Reference Document - Stormwater Mangement Report & Letter Repsonse - MCU24 0094 · MCU24/0094

Requested Information:




Response
A DRAINS model has been built to quickly assess the increase in peak flow off site which has indicated
3L/s for the 10% AEP event and 1L/s for the 1% AEP event and does not consider any stormwater directed
to the infiltration trench though standard losses in line with ARR Data Hub figures have been modelled.
The catchments set up are summarised below:
    • Area – 3520m2 (for both)
    • Fi – 0.22 for existing & 0.44 for developed
    • Tc – 5 mins for impervious areas 9 minutes for pervious areas
This minor increase is considered to be a result of the larger pervious portion of the site dictating the
regime of the peak flow rate for both cases. The infiltration trenches are therefore considered adequate
to ensure no adverse impacts off site as the infiltration rate will more than offset the minor increase in
peak flow.

Any stormwater surcharging from the trenches will have adequate travel distance to the boundary to
ensure sheet flow will be achieved as both trenches are more than 10m from the rear boundary.


Requested Information:




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