Our places: Ashley Rakahuri Rivercare Group
Image: Cody Whitelaw
Context, origins, and purpose of the group
The Ashley Rakahuri River just north of Rangiora is a globally rare ecosystem called a braided river, which by definition exists entirely because it’s on a braidplain.
Flowing from the mountains to the sea, braided rivers supported some of the most biologically rich and diverse landscapes on Earth. Hydraulically-connected to the main river channels are the springs, wetlands, and small streams on the braidplain that act as lungs and kidneys. They filter water, recycle nutrients, drawdown and store carbon dioxide, provide healthy habitats for plants, animals, and people. They also provide clean and plentiful mahinga kai, allow periodic high water flows to deliver sediment to the coast, protecting it against storms and rising sea levels, and help temper the energy of floodwaters by allowing them to spread out across a wide area.
In 1999, concerned by the declining state of the river, members of the community came together and formed the Ashley-Rakahuri River Rivercare group, ARRG. While different interest groups, from gravel extractors and 4WD enthusiasts to bird watchers, are often on opposing sides of issues, they had a common desire to reverse the decline in numbers of the unique endemic birds that breed on the river.
Like most of endemic species, these birds had evolved to take advantage of a unique specialist habitat, by nesting almost exclusively on the bare shingle of braidplains. This ecosystem remained free of predators and weeds until the arrival of humans. Failing to recognise braided rivers as essential life-supporting ecosystems, their braidplains were converted to agriculture, planted with exotic trees, and engineered into increasingly narrower channels to prevent flooding.
Key Actions
From the outset, ARRG worked together with the Department of Conservation, Environment Canterbury, and the Waimakariri District Council to develop and implement a strategy to manage an 18km section of the river from the confluence of the Okuku River (Fig. 2) downstream to the State Highway 1 (SH1) road bridge. Regular pest trapping, bird monitoring, and public education campaigns began in earnest in 2004.
They applied for and received funding from WWF, Pacific Development and Conservation Trust, NZ National Parks and Development Foundation, and the NZ Lottery Grants Board.
Today, volunteers build, install, and check predator traps, monitor bird populations annually, undertake field research, support graduate student research, trial programmes to enhance habitats through weed clearing and island formation with help from local gravel extraction company Taggart Earthmoving, and undertake community education programmes.
Apart from large one-off projects, they are largely self-funded through the work of volunteers, with additional sponsorship from local business Karikaas, artisan makers of a ‘braided river birds’ series of award-winning cheeses.
How this helps mitigate and adapt to the impacts of climate change
- Enhancing bird habitat also helps restores the life-supporting ecosystem services provided by the river. Wetlands and springs help act as a buffer against droughts, predicted to have an increasing severe impact on North Canterbury.
- Advocacy to restore large areas of the braidplain will also reduce the physical exposure to and mitigate the impact of floods, which are predicted to become more frequent and more severe.
- Actively engaging in public awareness of the problems facing river, including the risks of flooding from a severely restricted braidplain (Fig. 2 and 3) will help the community make better informed decisions about the future management of the river,
- This in turn reduces the socioeconomic vulnerability to hazard impacts and strengthens people’s resilience to disasters.
- Restoring wetlands along the braidplain will draw down carbon dioxide, creating a long term carbon sink that far exceeds the short-term benefits of carbon drawdown by exotic trees.
Left: Aerial photo c. 1944: Canterbury Maps historical image galley
Right: Aerial image Google Earth 2018
Fig. 2: The Okuku River (top centre left) merging with the Ashley Rakahuri, which then flows downstream past Rangiora (image at top of page) to the estuary (Fig. 1). Red arrows signify the width of the braidplain. Inside the yellow line is the approximate extent of the braidplain based on the geomorphology, i.e., indentations in the land showing where the braided channels were active prior to European settlement. Back then, the braidplains were largely free of vegetation other than low-lying native herbs and cushion plants, with smaller native shrubs interspersed with wetland vegetation around springs.
The scars of old channel are evidence that these rivers periodically flowed well outside the yellow lines.Reducing the width of the braidplain so that just a few channels are allowed to flow in a confined space has destroyed most of these ecosystems and the essential services they provide.
Climate change is leading to more droughts, exacerbating existing ecological problems. It’s also leading to higher bursts of rainfall that exceed the artificially restricted carrying capacity of the river, leading to flooding. Digging deeper channels by removing shingle and/or building higher stopbanks does not dampen the energy of floodwaters, which are set to increase in frequency and intensity as the climate continues to warm.
