2018-05-08 Services & Organisation Committee Agenda

SERVICES & ORGANISATION COMMITTEE MEETING AGENDA                                      8 MAY 2018




                                 Figure 1: Six Mile Creek Flood Plain


2.   Lake Macdonald Flood Working Group Investigation

At the commencement of the study, the Lake Macdonald Community Reference Group was
initiated to provide open communication with the community, through public forums, site visits
and consultation. The concerns from this group centred on the perceived worsening of flood
outcomes from 2010 and the influence, if any, from upstream development and the influence of
hydraulic structures within the flood plain including a new water pipe crossing and water retention
structures. A specific investigation of these questions was part of a sub-report of the Six Mile
Creek project that investigated these questions and looked at potential flood mitigation options
for this community.

To analyse the impact on the Lake Macdonald community due to upstream development, the
report looked to compare two different scenarios; development intensity from pre-2000 as well as
the full allowable development within the Noosa Plan. To make the comparison more
conservative, the future model assumed that no water retention devices would be installed within
new development areas and therefore the full runoff would enter the catchment. While this
comparison showed minor increases in flooding in the Cooroy region (that would be offset by
retention devices), the comparison showed no difference on impact to the Lake Macdonald
community due to the restriction of flow when passing under the railway line at Elm Street.

The Lake Macdonald community also raised concerns that a new water pipe installed adjacent to
Lake Macdonald by Seqwater was creating a blocking affect and subsequently worsening
flooding for their community. To analyse this, the model was varied to include a full blockage up
to the height of the pipe; however, due to the relatively small cross section of this blockage when
compared with the total flood plain, there was no change to peak flood levels.




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