Appendix B - Engineering Letter

4. Aseparate flooding problem exists for the properties 31, 29, 27 and 25 Tait Street. Our
Clients 0.7ha of un-developed land slopes toward the rear of these properties and floods
through their yards onto Tait Street.

This problem was addressed by Council approximately 15 years ago by the construction of an
extension of the underground drainage system along the frontages of these properties.

We designed this system for Council. The system is in place even though no records exist. Its
purpose was to allow residents to run a stormwater pipe from our Clients land boundary
through to the piped extension so as to alleviate the flooding. Unfortunately from discussion
with owners they were not aware of this option.

Unfortunately there is no room between houses 31, 29, 27 and 25 Tait Street and their side
boundaries to allow a 3m wide overland flow path and underground drainage. There is however
enough for a 1.5m wide interlot drainage outlet which our Client has negotiated permission from
the Owner to construct. This will allow properties in our Clients development on the low side of
the new road to drain to Tait Street.

Flooding Solutions Investigated to Date:

1. Our Client first investigated buying the property at No.14 Eagle Drive, removing the
house and placing a bioretention basin and detention basin in the property with a new
large underground drainage system through this block to the park.

We did a costing for this work which our client the checked against the development budget
and found the $450,000 cost of the house made this small development not viable.

2. We then suggested that Council be approached to allow a relaxation of their requirements
to retain most of the house on a smaller 450sqm lot with a 3m wide overland flow path,
larger underground drainage path and bio basin/detention basin in the remaining area
between the park and the house which would be given to Council as park.

This option was modelled and a design prepared and costed. It involved removing
approximately 1m of the house. This was submitted to Council but rejected mainly as being
difficult to maintain (refer to Plans 1403-10A & 02B).

3. We then investigated the alternative of placing a bioretention basin and detention basin
inside the development and piping the overflow down the side of No.14 Eagle Drive.
Two options were investigated:

a) Underground detention storage with bio tree pit gardens behind the kerbs
b) Using a development lot to place the detention basin and bio basin beside the
entrance to the development.

Option A proved not possible due to the large volume of storage required in the road reserve.
Option B proved feasible but would only solve the problem of flooding the residents at 31,29,27
and 25 Tait Street and leave the flooding of No.14 Eagle Drive unresolved as the existing non
subdivision contributing catchment is still of a similar size.

Conclusions:

That there are two possible solutions for the development:
(a) Bio basin and detention basin inside the development (refer to Plan 1403-10B,1403-
11B,1403-12B,1403-14A)

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