GRFMA Mapping Project

The report to review the design of the South Para Reservoir found that the North Para dam was less effective in mitigating flood flows than was determined by the hydrology review in 2003 with the target flow downstream of the Gawler River junction of 150m3/sec being exceeded somewhere between 20 and 50 year ARI, rather than 100 year ARI.

This means that for the very infrequent, but very large floods beyond a one in fifty year storm event that parts of the lower floodplain will still be at risk of flooding after the construction of the Bruce Eastick North Para Flood Mitigation Dam and modifications to the South Para Dam wall and spillway. The proposed modelling of one in 100 year rainfall event will identify these areas at risk in the event of such an exceptional flood.

The State Government, the four floodplain Councils of Gawler, Light Regional, Mallala, and Playford together with Buckland Park Developers are funding the project.

Stage One of the Mapping Project was completed on 29th February 2008. The Technical Report Volume 1, the ARI 100 Inundation Plan and the ARI 100 Flood Hazard Plan can be downloaded from this page.

Stage Two of the Mapping Project was completed in December 2008. The Flood Mitigation Options - Preliminary Assessment Stage Two Report can be downloaded from this page.

All enquiries regarding the interpretation of the Plans as to how they may influence the development potential of land or the relevant development plan should be directed to the respective Council

South Para Works Addendum

In September 2009 additional floodplain mapping was undertaken to identify the impact of not undertaking the South Para Reservoir Works. This involved running the floodplain model for ARI 100, 50 and 20 to identify if htere was a 'difference' to the impact of flooding. The modelling found that in the ARI 100 there was only slight increase in the depth of flooding with only small areas of additional flooding at the margins of the flooded areas. For the ARI 50 there was only a small increase in the depth of flooding with small additional areas of flooding at the margins. However in the ARI 20 there was a significant breakout at Wingate Road with significant additional flooding in the Gawler River, Lewiston and Virginia districts.

To quantify the damages further assessments identified that without the South Para Works the Gawler River will flood at Bakers Road in a ARI 10 flood event causing downstream flooding in the Virginia District.

The Australian Water Environments Flood Damages Estimates – South Para Reservoir Flood Mitigation Works December 2009 concludes ‘that the benefit cost ratio is more than 5’, ‘the works on the South Para Reservoir can be justified from a cost benefit perspective because the present value of benefits are significantly greater than the present value of the cost of the proposed works’, and ‘that the average annual damages associated with flooding of the Gawler River will remain high (over $6 million) and significantly greater than what previously would have been anticipated’.

A copy of the report and Mapping Difference maps can be downloaded from this page.

GRFMA _100yr ARI_A1_Inundation_20080229(2017 kb)
GRFMA Addendum ARI 10 Inundation 20091120(1004 kb)
GRFMA Addendum ARI 20 Depth_Diff_extent 20091028(1013 kb)
GRFMA Addendum ARI 50 Depth_Diff_extent 20091029(1009 kb)
GRFMA Addendum ARI 100 Depth_Diff_extent 20091029(1028 kb)
GRFMA Floodplain Mapping Stage 1 Report 20080229(17633 kb)
GRFMA Floodplain Mapping Stage 2 Report 20081209(7764 kb)
GRFMA South Para Works Cost Benefit Report Final 20091211(421 kb)
GRFMA_100yrARI_Hazard_A1_20080229(1981 kb)

 

Gawler River Floodplain Mapping Report 2015

The Gawler River Floodplain Management Authority (GRFMA) recently commissioned Australian Water Environments (AWE) to update floodplain mapping (2007) to help develop a better understanding of the extent, depth and hazard of flooding in the Gawler River floodplain. The report provides a description of the flood behaviour of the Gawler River, a review of the hydrological analysis for the 2007 floodplain mapping, and provides updated flood maps for the current conditions for the 1 in 50 ARI, 1 in 100 ARI and 1 in 200 ARI.

A copy of the report and Mapping Difference maps can be downloaded from this page.

Gawler River Floodplain Mapping(5579 kb)
Gawler River Flood Map 2015 (1 in 50 ARI Flood Hazard)(1170 kb)
Gawler River Flood Map 2015 (1 in 50 ARI Flood Inundation)(1211 kb)
Gawler River Flood Map 2015 (1 in 100 ARI Flood Hazard)(1205 kb)
Gawler River Flood Map 2015 (1 in 100 ARI Flood Inundation)(1259 kb)
Gawler River Flood Map 2015 (1 in 200 ARI Flood Hazard)(1214 kb)
Gawler River Flood Map 2015 (1 in 200 ARI Flood Inundation)(1272 kb)

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