Appendix D - Engineering Report

ENGINEERING REPORT
Address:     135 Lake Weyba Drive, Noosaville
Applicant/Client: Wag Investments (Andres Gabarrin)
1.       Background

Tod Consulting have been engaged to provide technical advice on the impacts of a proposed
development at 135 Lake Weyba Drive, Noosaville (Lot 1 RP 36729). The property is zoned for urban
detached housing but is also within the flood hazard zone. It is also acknowledged that the southern
section of Lake Weyba Drive becomes cut off from Weyba Rd during flood events which is a concern
for Council. The purpose of this report is to assess the likely earthworks (filling) requirements to
establish house sites within the proposed lots above the defined flood level, determine the impacts on
the surrounding flood levels as a result of these works and how these will be mitigated/minimised, and
to address stormwater management for the site.

2.       Earthworks for house pads

It is proposed to construct three house pads approx. 500m2 each within proposed lots 1, 2 & 3. Lot 4
contains an existing dwelling which will be retained and unaltered regarding floor level. Refer preliminary
earthworks drawing attached. The defined flood level for the area is expected to be RL 2.0m AHD and
the required freeboard 800mm due to proximity to Noosa River, giving an earthworks pad level of
RL2.8m AHD. The existing ground level within the proposed house site areas varies between RL 1.25
and 1.50m AHD so filling of approximately 1.5m is required. Modelling of the earthworks has determined
that the volume of fill required is in the order of 2310m3 of which 1067m3 is below the defined flood
level (RL 2.0 AHD). It is estimated that approximately 500m3 of fill can be obtained within the existing
site (below the defined flood level) with the balance being imported fill.

3.       Flood assessment - Levels

As noted above approximately 1067m3 of fill is required between the existing levels and the defined
flood level to establish the house pad areas. The impacts on the surrounding flood levels as a result of
this fill is partially offset by the cut within the site below the defined flood level of approx. 500m3, leaving
a total of 567m3 of fill within the floodplain that has not been offset. This volume displaces flood waters
in this area which has the potential to raise flood levels however as this volume is applied over the local
flood plain area the impacts are virtually insignificant. Conservatively the area of the surrounding
floodplain could be defined as the area upstream of the Eenie Creek Rd bridge over Weyba Creek.
Arguably this could include the whole of Lake Weyba, however for this exercise this has been excluded.
The attached plan shows and the floodplain in this area is over 390 Hectares. Once the displaced
volume is applied over this area the increase in flood level that results is less than 0.15mm.

4.       Flood assessment – emergency access

As outlined in section 1 of this report Lake Weyba Drive is cut off during significant flood events which
is a concern for Council in regard to providing access to emergency services. Whilst this is
acknowledged due to mechanism of flood in this area residents have significant lead time warning them
of such an event and can therefore self-evacuate (if they deem this necessary) prior to being cut off.
This flood behaviour is outlined in section 2.6 of the Noosa River Flood Study 1995 (John Wilson &
Partners and updated in 2000 by Lawson & Treloar) – extract attached. As noted in this section,
“because of the influence of the four large lakes and relative effects of rainfall and storm surge flooding,
flooding behaviour along the Noosa River, especially in its lower reaches is characterised by….the
Noosa River floodplain being flooded to relatively low depths by generally slow moving
floodwaters….Extended periods of relatively high flood levels……AND….A relatively long available


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17623 - 135 Lake Weyba Drive – Engineering Report – Draft