The Riverbank Road Floodbank Stabilisation project resulted from significant damage to the Lower Clutha River sustained in the February 2020 flood.
Now complete, this project reduces the risk of inundation to 1,300ha of productive farmland, homes and community assets. The project supports the entire Lower Clutha Flood Protection and Drainage scheme that provides protection to approximately 9,300ha in the Clutha delta.
The project team employed a range of repair approaches, including the use of environmental vegetative solutions, battering back and reshaping the damaged and eroded area of floodbank, stabilisation using coconut matting, and planting grass and trees to stabilise the bank longer term.
Otago Regional Council Manager of Engineering, Michelle Mifflin says that stopbank stabilisation with rock was used on the more complex section of the river upstream of the Stirling Bridge, near Balclutha.
“With very little space, the steep rock lined stopbank had scoured away and was collapsing upstream of the Riverbank Rd bridge at Stirling putting the bridge at risk. The repair involved re-lining the toe of the stopbank with rock riprap and keying this into the riverbed to prevent any further slumping”.
An access track was created at the waterline to allow for excavation into the riverbed and laying of the rock foundation. Approximately 3,500 cubic metres of rock was used for these works to re-establish rock protection along 300m of floodbank.
During excavation of the riverbed, timber beams from an historic, pre-1900’s bridge were uncovered. Works stopped for a week and an archaeological assessment of the beams was undertaken. Despite the delay, works were completed in mid-May, two weeks ahead of schedule.
Environmental benefits of the project include vegetative planting along 400m of riverbank and providing direct flood protection and reducing the risk of inundation to 1,300ha of productive farmland, homes and community assets.
The Riverbank Road stopbank stabilisation project has been successfully completed ahead of schedule and under budget providing employment opportunity within the local region and achieving significant environmental flood protection benefits.
This project has been partially funded through Kānoa, the Regional Economic Development Unit of the Ministry for Business, Innovation and Employment (MBIE), as one of the post-Covid 19 Shovel Ready projects.
Key facts
- Project budget $1,000,000. Completed cost $940,000
- 25 months (FTE’s) of time on the project
- Women (22%), Maori (4%), Apprentices (8%), Youth aged 15-24 (5%) of FTE’s
- Five direct suppliers (4 local) have provided services on the project.
