Gawler 2013-14 Annual Report - page 162

Town of GawlerAnnual Report 2013/14
Page162
introduction • summary • strategic directions •
statutory information
• index
Gawler River FloodplainManagement Authority
Annual Report 2013
2014
SouthParaReservoirModifications
To further improveprotection of the populationat Gawler and the downstream floodplain,
mitigationworkswere necessary at SouthParaDam.
SAWater was approached by theGRFMA inSeptember 2001, todiscuss the
implementation of floodmitigationworks at theSouthParaDamas part of their overall flood
mitigation strategies.
Undertaking the floodmitigationworks concurrentlywith a proposeddam safety upgrade
was seen as themost economical solution to achieve compliancewithANCOLDguidelines,
whilst providing considerableadditional benefit to the community. The floodmitigationwork
involvedmodifying the existing spillway crest by raising it by 1.57m. A10m central slot
remained at theoriginal full supply level toprovide a 1 in 100 year flood event flood retention
capacity. The height of the damembankment crest was raised2m by adding 1mof
additional fill and installing a concreteparapet wall on top toaccommodate the resultant
increased flood level.
Since that time, SAWater has beenworkingwith theGRFMA for the joint development of
theSouthParaReservoir to improve floodmitigation on theGawler andSouthPara rivers,
and dam safety improvements for the reservoir itself.
Detailed designworkwas completed inSeptember 2010 at a total project cost inexcess of
$7.5million excludingGST. TheGRFMAportionof the project cost is $4,013million.
A contract was awarded for the construction of theworks on 12 July 2011. Practical
completionwas achieved on 25 June 2012and the contract was completedwithout any
variations andon time.
GawlerRiver FloodMitigationSchemeMarkTwo
TheBoard considered thebest approach to addressing thenext stage in its BusinessPlan,
which is theGawler River FloodMitigationSchemeMark Two.
The studies into the flood issues in the region had identified that although the construction of
theBruceEastickNorthParaFloodMitigationDam andmodifications to theSouthPara
Reservoir have beenmost successful, there remains 3750 properties still at risk of
inundation in a1 in 100 year flood. Options to rectify this situation include the construction of
levees at Gawler, AngleVale, TwoWells andVirginia and thedevelopment of additional
floodmitigation storageon theNorthParaRiver.
Decisions in relation to the best optionhad to take into account a vast rangeof issues
including accommodating rail and road corridors, cost effectiveness and themost reliable
mitigation for theseproperties. As the variables and consequences of both options arewide-
reaching, theGawler River FloodplainManagement Authority decided toengage
professionals to investigate thematter further and toprovide aFindingsReport. Thebrief for
the report was basedonamethodology supportedby theDepartment of Planning, Transport
and Infrastructure.
At thebeginning of the year tenderswere called for appropriateprofessionals to provide the
AuthoritywithaFindingsReport and inMay 2014, AustralianWater Environmentswere
appointed to this task.
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