The failure of a constructed waterway near Donnybrook Rd Mickelham was highlighted last year by Merri Creek Management Committee (MCMC) in our Muddy Merri Troubles Report. Behind the scenes, Melbourne Water have been working to rectify the problems exposed by this waterway. They recently provided a welcome update to MCMC on progress on this matter.
Melbourne Water have also acknowledged the widespread occurrence of problematic soils in the Kalkallo Creek sub-catchment of the upper Merri (west of the Hume Highway between Donnybrook Rd and Beveridge). They will require all future developers to address the issue of erosive/dispersive soils earlier in the planning/design process to avoid similar problems occurring.
Read more below for full comments from Melbourne Water and an outline of the rectification options.
Photo: Constructed section of Donnybrook Creek south of Donnybrook Rd, Mickelham, August 2018. The channel is eroding, rilling erosion can be seen under the jute matting (dark lines), the jute matting has been ripped apart by high flows, and the slopes above the jute matting are poorly stabilised and eroding.
Melbourne Water comments regarding failure of constructed waterway at Donnybrook Rd, Mickleham
"Melbourne Water is aware of the failure of a constructed section of Donnybrook Creek on the southern side of Donnybrook Road, Mickleham. Melbourne Water have been actively working with the developer and their engineering consultant to rectify this issue. Investigation into the failure shows that the Kalkallo catchment is susceptible to highly erosive/dispersive soils which did not sustain the waterway that was designed and constructed. The constructed waterway is within the defects liability period and has not been accepted or handed over to Melbourne Water for ownership and maintenance. Melbourne Water’s acceptance for the handover of this asset will require the failure to be addressed.
Melbourne Water has met with the developer and consultant to discuss a number of rectification options including:
- Widening the waterway to reduce the velocities and shear stress in the channel.
- Constructing drop structures to flatten the longitudinal grade of the waterway.
- Replanting the waterway to create a vegetated core riparian zone and replace vegetation lost in the failure of the channel
It is expected that rework will occur in late winter-early spring 2019, with re-planting to occur immediately after the civil works.
Melbourne Water notes that the erosive/dispersive soil is widespread amongst the Kalkallo catchment, with the issue being prominent in areas where the integrity of the surface is being disturbed. As such, Melbourne Water will be requiring all future developers to address these issues earlier in the planning/design process."