Gawler 2012-13 Annual Report - page 158

Town of Gawler Annual Report 2012/13
Page 158
introduction • summary • strategic directions •
statutory information
• index
Gawler River Floodplain Management Authority
Annual Report 2012 – 2013
South Para Reservoir Modifications
To further improve protection of the population at Gawler and the downstream floodplain,
mitigation works were necessary at South Para Dam.
SA Water was approached by the GRFMA in September 2001, to discuss the
implementation of flood mitigation works at the South Para Dam as part of their overall flood
mitigation strategies.
Undertaking the flood mitigation works concurrently with a proposed dam safety upgrade
was seen as the most economical solution to achieve compliance with ANCOLD guidelines,
whilst providing considerable additional benefit to the community. The flood mitigation work
involved modifying the existing spillway crest by raising it by 1.57 m. A 10m central slot
remained at the original full supply level to provide a 1 in 100 year flood event flood retention
capacity. The height of the dam embankment crest was raised 2 m by adding 1 m of
additional fill and installing a concrete parapet wall on top to accommodate the resultant
increased flood level.
Since that time, SA Water has been working with the GRFMA for the joint development of
the South Para Reservoir to improve flood mitigation on the Gawler and South Para rivers,
and dam safety improvements for the reservoir itself.
Detailed design work was completed in September 2010 at a total project cost in excess of
$7.5 million excluding GST. The GRFMA portion of the project cost is $4,013 million.
A contract was awarded for the construction of the works on 12 July 2011. Practical
completion was achieved on 25 June 2012 and the contract was completed without any
variations and on time.
Gawler River Flood Mitigation Scheme Mark Two
The Board is now proceeding to the next stage in its Business Plan, which is the Gawler
River Flood Mitigation Scheme Mark Two:
Step One:
Reconfirm with the Constituent Councils that a 1 in 100 year level of
protection is the protection standard that is to be pursued in the development
of the Gawler River Flood Mitigation Scheme - Mark Two Strategy.
Step Two:
Determine if a second dam on the North Para River is an option, taking into
consideration opportunities to pursue either an evacuation model or detention
model.
Step Three: The Gawler River Floodplain Mapping Model should be maintained as the
reference tool to demonstrate the level of flood protection and validity of
design of land proposed for development as part of the approval process. To
achieve this, the model should be updated to include recent works such as
the Northern Expressway works, modifications to South Para Reservoir
spillway and dam wall and the additional floodplain mapping completed as
part of the Light River Templers Creek Salt Creek Mapping Study by the
District Council of Mallala.
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