1211 - Engineering Report Complete C · 132002.220527.1

overflow drainage path that can never be blocked, and surface levels that grade away

from the ground floor level of the house.

2.3 Proposed Drainage System

Please refer to our attached Drawing No. 1211/P02 which shows the proposed new
drainage system to the altered residence.

There are several features to note:
Firstly, all runoff from the driveway will be directed into a side entry gully pit (Council
standard) which cannot be blocked (i.e the overflow from the grate is still intercepted in

the side letterbox opening which is lower than the paved driveway).

Secondly, the underground drainage system will be designed for a 10 year ARI storm

event, which is much greater capacity than current system.

Thirdly, the finished surface level of the driveway and forecourt will be lowered and graded

away from the ground floor level of the house alterations.

Finally and most importantly, an overflow flow path is diverted around the house.
Therefore even if all the underground pipes become blocked, the surface levels will direct
a 100 year ARI storm runoff away from the house and around the southern part of the
house alteration. Therefore there will be no storm events that can inundate the altered
house floor levels.

2.4 Stormwater Discharge

Please refer to attached Geotechnical Report No.14169-001-RevO by Tectonic
Geotechnical & Environmental Engineers. They were tasked with identifying a safe and
secure method of discharging stormwater from the site, which did not cause erosion or

instability to the site.

To ensure stormwater runoff quality, every stormwater collection pit will be fitted with an

approved filter basket to remove gross pollutants.

Permeability results from the site show that a lined infiltration bore 5 metres downstream
of the house provides the best solution for stormwater discharge. Please refer to our

Drawing No. 1211/P02 which shows the infiltration bore proposed. The proposed

 

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1211-ENG-01_Version 1.0 (April 2015)