2 David Low Way - Attachment 4 - Specific Engineering Assessments - Cardno 10-8-17

753345 6
9 August 2017

Stormwater Management

The site is effectively its own catchment, encompassing the plateau which sits above the most landward
sand dune. The site has a total area of 9,677 m2. Under the worst possible development conditions for
water quality purposes, it has been assumed that the site could consist of approximately 4,000 m? of
roof and hardstand area. It has been recommended that each dwelling on the site be fitted with a water
tank with a volume of 10,000 L. The potential for water quality impacts external to the site are
considered minimal in the context that the site consists of clean beach sand with little potential for
contamination. If water quality treatment is required, it is proposed that individual bio-retention filters be
constructed on each proposed allotment. Each filter should have an area of approximately 30 m%, if
Council determines that such treatment is required.

Alternatively, and given the sandy nature of the site, it is proposed that all stormwater generated on the
sire could be directed to small infiltration basins to be constructed for each dwelling. A basin with
surface area of about 70 m? per residence, and a depth of about 300 mm, will be sufficient to manage
all stormwater runoff from the site.

Conclusions

A number of specialist engineering investigations have been undertaken for the proposed project. It
has been determined that there are no issues in the following study areas which would prevent the
proposed 6 lot subdivision from proceeding as planned.

Coastal Hazard and Erosion

Flooding

Acid Sulfate Soils

Geotechnical Assessment for Land Instability
Stormwater Management

Yours sincerely

 

Dr Trevor Johnson
Engineering Consultant

Enel: Subdivision Proposal Plan
SARA Coastal Mapping
Coastal engineering report
State Code 8 compliance
Natural hazards overlay code compliance
Geotechnical report

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