Earth and repair work on a massive scale is still being undertaken in the Eastern Bay of Plenty 12 months on since ex-cyclones Debbie and Cook brought rain, wind and widespread flooding to the area.
Bay of Plenty Regional Council’s project manager of flood recovery Paula Chapman says in total 520 sites of river bank or drain damage have been identified from the Kaituna Catchment Control Scheme through to the Waioeka-Otara Rivers Scheme.
“Over 50 per cent of the work sits within the Rangitaiki-Tarawera Rivers Scheme and around 25 per cent is in the Whakatane-Tauranga (formerly Waimana) Rivers Scheme.
“So yes, adding in Opotiki with 10 per cent; the impact for the Eastern BOP is significant.”
Paula says to date 82 sites out of the 520 have been completed and she expects the work to be at least a three-year project. “All going well we are aiming for completion summer of 2020.”
The work involves the repair of existing assets, in some cases construction of new assets and also river channel realignment, says Paula.
“Assets include rock amour protection, tied tree groynes, willow planting, repair of pump stations, drain bank repairs. Work involving the protection of community assets – like roads, water supplies, stopbanks, urban areas – are assessed as the highest priority.”
The priority of sites is based on the risk of the site becoming worse and the consequence of the site becoming more damaged and the practicalities of completing the work.
“Where a community asset is at risk – a road, water supply, marae, flood protection stop bank etc – the site is elevated to very high priority.”
The biggest job scheduled is the realignment of the College Rd stopbank in Edgecumbe.
“The removal, demolition and tidying up work is almost complete on the sites BOPRC acquired that will enable the stopbank and road realignment,” says Paula. “Fences are being erected on the neighbouring properties.”
The contract for the construction works had been awarded and work on-site was set to begin mid-March, with substantial completion programmed for August.
“The regional council’s engineering team has worked closely with the Rangitaiki Community Board and the Whakatane District Council Recovery Team on the design, project plans and progress,” says Paula.
Other large jobs have been tackled in the last 12 months too.
Alongside the Ruatoki Township a deflector stopbank was damaged and at threat of being undermined. The village was evacuated at the time, says Paula, with repair involving rock lining “and repair to and strengthening of the stopbank”.
A job on the Whakatane River (Simpsons) just outside of the Whakatane township involved rock armoring to protected a major rural 100-year stopbank. “The damaged riverbank had eroded to within 10m-15m of the stopbank, taking with it well established willow tree edge protection. Approximately 4500 tonne of rock was used in this repair job,” says Paula.
Repairwork to the damaged R Brown Site – at Otara River in Opotiki – involved 220 lm of eroded riverbank threatening a rural stopbank, and power supply in rural Opotiki.
“The repair involved the reinstatement of the berm and part of the rural stopbank, and rock lining to strengthen the new berm. This work incorporated more than 2000 tonne of rock,” says Paula.
At the Wilsons site at Galatea major river bank erosion was causing significant meander change. “The impact of this change, if left, would likely lead to continued erosion of the river bank immediately downstream on the opposite bank. The work also involved some channel realignment and widening and rock lining to strengthen the eroded bank.”
Paula says her team did an estimate of the quantity of rock that would be needed to complete proposed rock works over the total project – for example, where rock work was proposed in the repair.
“This came out at more than 350,000 tonne – when you consider a standard truck-and-trailer unit holds approximately 21 tonne of rock that converts to a whole lot of truck movements during a three-year period.”
Paula says landowners need to be aware of future climate change– “and how this can impact ourselves and our communities”.
“There seems to be a much more frequent occurrence of significant weather events in New Zealand. “These are natural events and in many situations our rivers and waterways have been altered to provide for the way we live – farming, horticulture, community infrastructure, urban development etc – and are therefore not in a natural state.
“So there is a need to raise awareness of the risks and hazards of living alongside flood-prone areas, especially in light of climate change and increased frequency of extreme events likely in the Bay of Plenty.”