12 July 2019

Update on Brown Hill Creek flood mitigation

Related imageI asked the following questions at last month's Council meeting. You might be surprised at how much of the works has already been completed or is approved to be undertaken. The most disturbing information is that the widening and deepening of identified sections of the creek between Victoria St and Cross Rd will not be completed until 2035/36. By this time property acquisition costs will have escalated considerably and until this work is done flooding is still a significant risk in Unley's section of the Creek!

1. What projects for the entire Brown Hill Creek catchment have been completed so far?
Ridge Park Detention Dam – City of Unley. BHC Diversion Culvert by DPTI – City of Unley. Upper BHC – Hawthorn Reserve – City of Mitcham. Mount Osmond interchange dam modification. Currently in year 3 (2018/19) of a 20-year program to implement the flood mitigation works.
2. What projects for the entire Brown Hill Creek catchment are in the planning stage?
South Parklands – Victoria Park City of Adelaide (Public consultation of proposed works to close 5 July 2019. Construction to commence 19/20FY and be completed 2020/21). Page 411 of Council Agenda 24 June 2019 South Parklands – Park 20 City of Adelaide (Public consultation of proposed works to close 5 July 2019. Construction to commence 2020/21 and be completed 2021/22). Glenside – City of Burnside (Construction to commence as part of the Cedar Woods development at Glenside). Upper BHC Area 1 Wilberforce Walk (Anzac Highway to Third Avenue only) – City of Unley Construction to commence 2019/20 following land acquisition.
3. What projects have been identified but are yet to be planned or completed in Unley?
Brown Hill Creek – Creek upgrade areas (widening) Upper BHC Area 1 (Third Avenue – Forestville Reserve) Area 2 (Victoria Street – Mitchell Street & Orphanage Park culvert option) Area 3 (Douglas Street – Malcolm Street) Area 4 (Malcolm Street – Cross Road) Bridge/culvert upgrades – Second Avenue, Forestville First Avenue, Forestville Regent Street, Millswood Orphanage Park (internal road bridge) concept design through Orphanage Park yet to be confirmed Charles Street, Forestville Ethel Street, Forestville Northgate Street, Unley Park Goodwood Road Culvert Keswick Creek Le Hunte Street Diversion – All three sections (Program 2025/26 – 2031/32). Glen Osmond Creek Fern Avenue, Fullarton Bridge upgrade. Torrens Avenue, Fullarton Bridge upgrade. Minor upgrades along Glen Osmond Creek between Braeside Avenue and Burnham Avenue.
4. For each project completed so far how much has the risk of flooding in Unley reduced?
It is not possible to quantify the exact extent of reduction in flood risk, however, in the proximity of each project and immediately downstream there is a significant reduction in flood potential. The projects completed and soon to be completed in the next few years have/will greatly reduce the risk of flooding along Glen Osmond Creek, Parklands Creek and, to some extent, Keswick Creek. The minor projects that have been completed along Brown Hill Creek have had little impact on flood reduction accept in the local area of the works.
5. At what point will the risk have been reduced to an acceptable level?
The  widely  accepted  stormwater  industry  standard  for  flood  protection  is  100yr  ARI  (Average Recurrence Interval) or 1% AEP (Annual Exceedance Probability).  This standard  is what has been assumed in the BHKC SMP.  The project is scheduled to be completed  over 20 years and therefore the modelled 100yr ARI flood protection will not occur until  all  projects are  completed.  Within  the  City  of Unley –  the  Creek widening and  bridge  replacement  between  Victoria  Street  and  Cross  Road  (Area  2  ‐  Area  4  including  Orphanage  Park)  and  Glen  Osmond  Creek  minor  upgrades  are  the  last  projects  scheduled  and  are  proposed  to  be  completed  in  year  20,  2035/36.

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