Fact Sheet

Preliminary Assessment - Enhancement of Flood Mitigation Options

Preliminary Assessment - Enhancement of Flood Mitigation OptionsThe report investigates alternative supplementary works to reduce or eliminate the need for the flood control dam in Brown Hill Creek Recreation Park.The aim of these preliminary assessments has been to identify enhancements to the current preferred flood mitigation option which would achieve similar flood mitigation outcomes as detailed in the Draft Plan whilst also achieving comparative project costs and benefit cost ratios.The five preliminary options identified in the report were:Option 1 – Additional Bypas CulvertKey Features

• No dam in Brown Hill Creek Recreation Park• Increased length of high flow bypass culvert between Cross Road and Malcolm Street• Increased size of the bypass culvert• Increased channel upgrade works between Hampton Street and Cross Roads and from Leigh Street to Anzac Highway

Advantages• No dam

Disadvantages• Higher cost than recommended option by $6.5m• Potential conflicts if future arterial road overpass at Cross Road/Railway line proposed• Increasing the size of the culvert may not be possible due to conflict with existing services

Estimated Project Cost$139.5m ($6.5m higher than recommended option)Option 2 - Additional Channel UpgradesKey Features

• No dam in Brown Hill Creek Recreation Park• Increased size of the high flow bypass culvert from Malcolm Street to the Tramway• Increased channel works between Cross Road and Malcolm Street, Hampton Street and Cross Roads and from Leigh Street to Anzac Highway

Advantages• No dam

Disadvantages• Higher cost than recommended option by $10.6m• Significant property acquisition• I ncreasing size of the culvert may not be possible due to conflict with existing services

Estimated Project Cost$143.6m ($10.6m higher than recommended option)

A Draft Stormwater, Management Plan (the Draft Plan) has been developed to reduce the impact of major flooding across the catchment of the Brownhill, Keswick, Glen Osmond and Parklands Creeks that flow through the Cities of Adelaide, Burnside, Mitcham, Unley and West Torrens.

A Preliminary Assessment - Enhancement of Flood Mitigation Options, commissioned by the City of Mitcham, investigated variations to the current preferred option outlined in the Draft Plan to reduce or eliminate the need for a flood control dam.

Preliminary Assessment - Enhancement of Flood Mitigation Options

Option 3 - Additional Bypass CulvertFeatures

• No dam in Brown Hill Creek Recreation Park• Increased length of the bypass culvert between Hampton Street, Jervois and Malcolm Street• A new high flow bypass culvert between Malcolm Street and the Glenelg Tramway• Increased channel works between Leah Street to Anzac Highway

Advantages• No dam• Hampton Street to Cross Road channel upgrades would not be required• Lesser increase in total project cost by $3.8m

Disadvantages• Increasing size of the culvert may not be possible due to conflict with existing services• Increased disruption in Unley due to culvert construction

Estimated Project Cost$136.8m ($3.8m higher than recommended option)

Option 4 - 10 Metre High DamFeatures

• Reduced dam height to 10 metres (just above existing road level in Brown Hill Creek Recreation Park)• Minor channel upgrade works in Mitcham• Increased culvert lengths and sizes and channel upgrades downstream

Advantages• Reduced dam height• Total project cost similar to draft Stormwater Management Plan

Disadvantages• Dam in Brown Hill Creek Recreation Park• Increasing the size of the culvert may not be possible due to conflict with existing services

Estimated Project Cost$133.2m (nil increase from recommended option)

Option 5 - 8 Metre High DamFeatures

• Reduced dam height to 8 metres (approximately existing road level in Brown Hill Creek Recreation Park)• Significant culvert and channel upgrades downstream resulting in major conflict with existing services• This option provided insufficient detention of flood water

Advantages• Reduced dam height• Lesser increase in total project cost

Disadvantages• Dam in Brown Hill Creek Recreation Park• Insufficient flood water detention resulting increasing flooding throughout the catchment• The size of the culvert may not be possible due to conflict with existing services

Estimated Project Cost$136.6m ($3.6m higher than recommended option)

Preliminary Assessment - Enhancement of Flood Mitigation Options

Next Step

The Cities of Adelaide, Burnside, Mitcham, Unley and West Torrens have agreed to engage a consultant to confirm whether a culvert either 1.8m (as per the Draft Stormwater Management Plan) or 2.5m (as per Enhanced Options) can physically be constructed in the streets as identified in both the Plan and the enhanced options reports.

This investigation will also identify the extent of service conflicts and if an affordable deviation or service location can be undertaken along with channel upgrades. It is anticipated that this work will take 4-6 weeks.

Have Your Say

From Monday 31 October to Monday 12 December 2011 members of the public are invited to provide feedback on the Draft Plan.

A copy of the "Preliminary Assessment - Enhancement of Flood Mitigation Options" and the Draft Stormwater Management Plan is available on the City of Mitcham website www.mitchamcouncil.sa.gov.au, and can be viewed in hard copy at the City of Mitcham Civic Centre, Blackwood and Mitcham Libraries and on Council's website at www.mitchamcouncil.sa.gov.au.

Feedback will be considered in finalising the Draft Plan.

The City of Mitcham will take account of the results of the Preliminary Assessment - Enhancement of Mitigation Options as part of its submission on the Draft Stormwater Management Plan Brownhill Keswick Creek community consultation.

More Information

For more information please contact John Wiley on 8372 8888.