John Holland and KBR have completed an upgrade to the Lee Street retarding basin at Frankston on behalf of Melbourne Water, to ensure it continues to reduce the risk of flooding to the community.
Why this upgrade was important
Melbourne Water has over 200 retarding basins that we regularly assess for risks, conduct maintenance on, and upgrade as necessary. The Australian National Committee on Large Dams (ANCOLD) guidelines represents the best Australian and international engineering practice in the safe design, management and operation of dams. We use these guidelines to manage our retarding basins.
The Lee Street retarding basin was recently assessed against the ANCOLD guidelines, which found that upgrade works were needed to ensure the retarding basin continues to reduce flood risk and operate safely for the community.
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Scope of works
This project involved:
- removal of trees, root ball excavation and backfill of embankment
- partial reconstruction of existing embankment
- filter trench excavation and backfill
- filter drain outlet installation
- embankment hardening
- embankment crest capping
As a precaution, the project team hired a qualified wildlife handler with 25 years’ experience in zoology and ecology, to put community concerns at ease. The handler had a permit under the Wildlife Act 1975 and remained on site for the duration of the tree removal works.
Other actions to protect wildlife were as follows:
- A Flora and Fauna assessment was completed in the design phase.
- A wildlife pre-clearance check was completed before construction, including checking the site for fauna and marking trees likely to have habitat.
- Two wildlife handlers completed a walkthrough on the day of the tree removal and re-checked all hollows to make sure no wildlife had moved in, including checking higher locations via a boom (cherry picker).
- If fauna was found in the tree, the wildlife handler was to attempt to catch it (without chasing or causing distress). In the event the wildlife could not be caught, the handler was to encourage the fauna to move - and if not possible they were to move to the next tree and return to try again.
- To check for micro bats, the wildlife handlers had been lifting tree bark and checking in hollows and cracks. If any micro bats were found they were to be bagged, put in a dark, quiet, cool area and released at dusk, preferably on a mirror image tree.
- A number of nest boxes were purchased to install on the site to create more habitat.
- Nests in trees that were being removed were relocated. If they were intact, they were put next to the nest box; if not, the remnants were strategically placed in the nest boxes in trees to encourage the fauna into other trees.
- Hollow trees were retained for fauna habitat and moved down to the grassy area in the middle of the site.
- A fauna ladder was installed for connectivity for arboreal species.
- Flowering eucalyptus tree branches were retained as a food source for birds and some mammals, and being donated to wildlife carers/shelters.
- Seeds were collected from Eucalypt and Melaleuca trees and extracted, cleaned and processed to use for propagation for the local area. They were donated to Frankston City Council’s indigenous nursery.