GRFMA Bruce Eastick North Para Flood Mitigation Dam

GRFMA Bruce Eastick North Para Flood Mitigation Dam

The dam on the North Para River is a flood mitigation dam not a water storage dam. The purpose of the dam is to store the storm flow from the river catchment and allow it to flow down the river at a rate that will pass through the town of Gawler and the Lower Gawler River levees without causing flooding and damage. The effect of the dam will be that an ARI 40 event with a peak flow of approximately 310 cumecs that passes down the river in 18 hours will be reduced to 110 cumecs and take 4 days to flow down the river.

The North Para River Flood Mitigation Dam is situated 4.8 km NNE of the Gawler PO

The dam is constructed of Roller Compacted Concrete (RCC) using a “high paste” RCC that has a relatively high cement content, comprising Portland cement and flyash, mixed with rock and sand crushed from the same source that provides essentially a homogeneous structure with a low permeability.

The dam comprises a main dam wall with a crest 225 metres wide and stand 25 metres above stream level. The upstream face is vertical with a stepped (0.8 x 1.0) downstream face with side channels feeding to a stilling basin. River flows will be through a low level 2.1 steel pipe set just below the stream level to maintain environmental flows with two 1.8 metre pipes set 17 metres above the stream level. The main spillway is on the crest of the dam wall at a height of 82.5 metres and will begin to spill somewhere between a ARI 25 and ARI 50. On the eastern high level terrace adjoining the eastern abutment is the secondary spillway with a crest 220 metres wide at a height of 84.0 metres that will come into operation in a ARI 1,000 event.

All land flooded by the dam waters up to 84.0 metres is required to be under a ‘Right to Flood’ easement to the GRFMA for flood mitigation purposes.

GRFMA Dam Construction

The dam designers and construction Superintendent was URS Australia Pty Ltd and the principal construction contractor was Bardavcol Pty Ltd.

The construction was undertaken in two contracts, an Earthworks contract, comprising the excavation of the site, the construction of the Low Level Outlet Pipe and the construction of the cofferdam that commenced in September 2006 and ended in April 2007 and the Roller Compacted Concrete (RCC) contract that commenced in April 2007 and was completed in December 2007.

44,000 cubic metres of RCC was laid in the construction of the dam wall and secondary spillway.

Progress Reports and the Dam Opening Brochure that contains specifications of the dam wall and spillway can be downloaded from this page.

GRFMA Flood Events

Real Time Information

During a storm event the real time catchment rainfall, river flow data and height of water in the dam is able to be monitored on the Bureau of Meteorology website www.bom.gov.au/sa/flood/gawler.shtml

4th & 5th September 2010

On the 4th & 5th September 2010 heavy rains accross the catchment, up to 70 mm, estimated to be approximately a 1 in 7 year storm event, resulted in strong flows in the North Para River. Water began to rise behind the Bruce Eastick North Para Flood Mitigation Dam on Sturday and at 10. AM on the Sunday reached a maximum height of 70 metres AHD just below the high level pipes, which is halfway up the dam wall. Dam waters estimated to be 1.2 Gl extended approximately 4 kilometres upstream passed through the low level outlet pipe at a controlled flow returning to stream level at midday the following day.

Both the effect of the dam, and filling the South Para Reservoir mitigated the flow in the gawler River that caused flooding of grazing land just east and west of the new Port Wakefield Highway. No property damage was reported.

Had the Bruce Eastick North Para Flood Mitigation Dam not been in place it is estimated that a breakout just west of Bakers Road to the north would have occured flooding a number of horticultural properties.

While this storm event was at the smaller end of the scale it confirmed that the dam operated as designed and provided protection from flooding by mitigating the peak flow to a level that could be passed by the Lower gawler River without overtopping the private levees causing flooding as was the case in 2005 and 19992.

An Information Sheet showing the performance of the dam during this event can be downloaded from this page

8th December 2010

Following intense storms in the early hours of Wednesday 8th December 2010 where several centres in the catchment recorded 24 hour falls of 70 to 80 mm, that gave rise to strong flows in the North Para River that caused the Bruce Eastick North Para Flood Mitigation Dam to operate for the second time in four months. Water rose to 72.5 metres AHD which caused the two high level outlet pipes to operate for the first time. Dam waters estimated to be 1.8 Gl 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 the Bruce Eastick North Para Flood Mitigation Dam not been in place it is estimated that a breakout just west of Bakers Road to the north would have occured flooding a number of horticultural properties.

An Information sheet showing the performance of the dam during the flood event can be downloaded from this page.

GRFMA Bruce Eastick Dam 20100906(532 kb)

GRFMA Bruce Eastick Dam 20101208(283 kb)

After Hours Contact Call 08 8522 9211
 
43 High Street, Gawler East SA 5118
Tel: 08 8522 9211
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