Gawler 2013-14 Annual Report - page 161

Town of GawlerAnnual Report 2013/14
introduction • summary • strategic directions •
statutory information
• index
Gawler River FloodplainManagement Authority
Annual Report 2013
September 2010
Heavy rains fell across the catchment, up to 70mm, estimated tobe approximately a 1 in 7
year stormevent resulted in strong flows in theNorthParaRiver.Water began to rise behind
theBruceEastickNorthParaFloodMitigationDam onSaturday andat 10.00am onSunday,
reached amaximum height of 70metresAHD, just below the high-level outlet pipes. Dam
waters estimated tobe 1.2Gl extendedapproximately four kilometres upstream, passed
through the low level outlet pipe at a controlled flow, returning to stream level at midday the
following day. The real time catchment rainfall, river flow dataand height of water in thedam
were able tobemonitoredon theBureauof Meteorologywebsite.
Both the effect of thedam, and filling theSouthParaReservoir,mitigated the flow in the
Gawler River that caused flooding of grazing land just east andwest of thenewPort
WakefieldHighway. Noproperty damagewas reported.
December 2010
Following intense storms in theearly hourswhere several centres recorded 24 hour falls of
70 to80mm, that gave rise to strong flows in theNorthParaRiver that caused theBruce
EastickNorthParaFloodMitigationDam tooperate for the second time in fourmonths.
Water rose to 72.5m, which caused the twoHigh Level Outlet Pipes to operate for the first
time. Damwaters estimated tobe1.8Gl extended over 4 kilometres upstream passed
through the low level outlet pipe at a controlled flow returning to stream level by late the
following afternoon.
Had theBruceEastickNorthParaFloodMitigationDamnot been in place it is estimated that
a breakout just west of BakersRoad to thenorthwould have occurred, flooding anumber of
horticultural properties.
Theseevents confirmed that thedamoperatedas designedandprovided protection by
mitigating the peak flow toa level that couldbepassed by the lower Gawler River, without
overtopping thebanks causing flooding aswas the case in2005 and1992.
A replacement TurretfieldFlowGaugeWeir hasbeen constructed 800metres downstream
from the dam on theNorthParaRiver. The former flowgaugeweir just upstream of the dam
wall is drowned out in a flood event by the damwaters and has beendecommissioned. The
replacement weir is smaller in design, gauging flows up to approximately 300 cubicmetres
per second. Thisgaugeweir downstreamof the junctionwithWalker Creek provides flow
data from thewesternpart of the catchment. Data from this flowgaugewill be added to the
online real timedataon theBureau of Meteorologyweb site.
Two additional surveymonuments have been constructed at thedam site, to provide a total
of fourmonuments toprovide a survey base tomonitor the deformation stability of the dam
wall and spillway. Part of themaintenance program is toperiodically survey the structure to
ensure that there is nomovement. Inparticular this is performedaftermajor floodor seismic
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