Significant floods have occurred across the Canterbury region during the last three years. Candidates for Environment Canterbury agree flood management is an urgent problem – and no solution, including managed retreat, is off the table.
Most of the time, the Heathcote/Ōpāwaho is a placid sort of river, wending around the base of Christchurch’s Port Hills, river weeds and faded road cones lurking beneath the glassy green surface. In heavy rain, though, the river changes: brown and muddy, it overcomes its shallow banks and sloshes onto roads.
In the past few years, many Canterbury residents have experienced their local river flooding. The Ōpāwaho, management of which rests largely with Christchurch City Council, is one of the smaller awa in the region. River management is shared between local councils and regional council Environment Canterbury, which oversees the broad twisting strands of the Rakaia, Waimakariri, Waikirikiri, and the Rangitata rivers. Severe weather, including last year’s Ashburton floods and this year’s heavy rainfall in July, can quickly overwhelm rivers, which damage homes and infrastructure. Responding to this flooding has been a major task for the 2019-2022 term of Environment Canterbury.
When the Ashburton/Hakatere river flooded last year, the rain gauge at Mt Somers measured 526 millimetres of rain over 48 hours, the highest ever recorded. As climate change triggers more snowmelt and extreme rainfall events, the flooding of the last few years is set to happen again and again. This inevitable flooding will place infrastructure and farmland at risk, and presents an urgent challenge to council candidates – many of whom mention water as an urgent priority for the next term.
“There’s no such thing as a natural disaster, there are natural events that occur when homes and people and infrastructure are in hazardous places,” says Matthew Hughes, a senior lecturer at the University of Canterbury, who specialises in civil engineering in times of disaster. “Floods are a disaster when we build vulnerable infrastructure that [when damaged] causes widespread disruption to goods and services.”
Under the force of a flood, Hughes says, a lot of infrastructure is vulnerable. Because floods don’t happen most of the time, there is little redundancy in the system: why build an expensive backup bridge or two if the flooding that might wipe out the main one might only occur once in fifty years? But climate change makes rare events more likely – and Hughes points out that infrastructure, like the mouths of stormwater pipes designed for an expected maximum flow, hasn’t kept up with changing weather patterns and probabilities.
Involving communities in decisions
For candidates contesting council seats in Environment Canterbury’s local elections, floods are a significant concern. Many candidates mention flood protection, and climate change adaptation more broadly, in their candidate bios.
A “whole of river” approach to river management has been a crucial step in the right direction, says Grant Edge, a current councillor who is running again in the Ōpukepuke/North Canterbury constituency. This approach is in line with last year’s National Policy Statement on Freshwater Management. “It’s designed to put water first, people second and the economic issues third,” Edge told The Spinoff, adding that river management has to change as the threat of climate change increases.
Former Christchurch City Councillor David East, running for Environment Canterbury in the Christchurch North East/Ōrei constituency, worked at the North Canterbury Catchment Board before the boards were amalgamated into the regional council as part of the 1989 local government reforms. He says that changing this system has meant that some rivers, like the Waimakariri, are managed throughout their catchment, but others, like the Styx/Pūharakekenui and the Avon/Ōtakaro, are more inconsistent, especially after land subsidence following the Canterbury earthquakes. “We need to mitigate flooding on a catchment by catchment basis,” he says. As councillor he wants to deal with raw data, not analysed reports by consultants, and focus on “practical solutions”.
Clare McKay, also a current councillor for North Canterbury, says that conversations about changing flood management “can’t be put off”. Environment Canterbury has a catchment sub-committee, which deals with some bigger picture questions regarding managing water, and River Rating district liaison meetings, which are intended to give communities a voice to express concerns about their rivers.
Other candidates emphasise community involvement in river decisions, too. Brynlea Stocks, a consent planner running the Christchurch Central/Ōhoko constituency, is a current member of the West Melton Water Zone Committee, another mechanism that allows communities to have a say on river management. Stocks says that “connecting community groups into emergency planning, giving them access to resources and building infrastructure that is adaptive to drier and wetter conditions,” will allow people to adapt to expected floods.
Future options for river management
Already, Environment Canterbury is working on a variety of responses to flooding. Te Waihora/Lake Ellesmere in Banks Peninsula can be opened to the sea to manage flow and protect biodiversity. Often projects are very long term: since a massive storm in 1868, the Waimakariri river has been extensively managed, with the latest $40 million stopbank upgrade completed in 2019.
“When I was a young man, you could hear the river talking, stones fizzing against each other, the sound of slumping as shingle banks fell into the water,” says Peter Trolove, an Environment Canterbury candidate, semi-retired vet, and long-time angler. Because many of Canterbury’s big rivers move gravel eroded from the Southern Alps to the sea, lower flows caused by drought or irrigation lead to gravel build up, meaning that riverbeds are shallower when floods do come. Gravel extraction is currently carried out, deepening river channels to prevent floods and providing a useful material for construction work.
But this does limit a river’s natural inclination to change its course; Trolove says that when Environment Canterbury was run by commissioners, they “encouraged encroachment” around rivers, allowing farmland, housing, and infrastructure to be developed in places where they’ll be at risk. “Environment Canterbury has lost control of the river margins for flood protection,” he says. Like East, Trolove is also worried that the council isn’t reporting some of these risks honestly, and hopes that if he’s elected, he can change how information about water levels and pollution is reported.
For some of these at-risk locations, managed retreat needs to be a future option. “We can provide more [flood] protection, increase river capacity, [but] we will also have to discuss managed retreat to keep communities safe,” says McKay.
Iaean Cranwell, a former Environment Canterbury councillor who has been a Tumu Taiao (a Ngāi Tahu representative and non-voting member) during this term of council, told The Spinoff that managed retreat “is a hard conversation, we’ve invested so much in some areas that it’s hard to move.” But it may be necessary to protect people from the social and economic harm of repeated flooding.
“Those rivers have changed their course for so long and now they’ve been constrained so if a flood does come we have to have enough area.” As an alternative, Cranwell says that investing in nature-based solutions, including allowing gravel to flow and restoring wetlands, can help limit the extent of floods, as well as protecting biodiversity.
The long-term perspective
While Cranwell’s Tumu Taiao role is being replaced by Ngāi Tahu representatives on Environment Canterbury who have full voting rights, Cranwell says that as the regional council makes policy decisions that will endure long into the future, there’s an opportunity to learn from the past. Councils have been managing rivers to mitigate flooding for 150 years, but water has been flowing through Waitaha for thousands of years before that. “You can learn from the names,” he says. “Little River [in Banks Peninsula], where I’m from, is called Wairewa, which means fast rising water – because it has a big catchment, so the water can rise quickly on what is now. You can talk to mana whenua about what that river used to look like when you’re making decisions.”
Often, decisions like how a new development creates stormwater infrastructure, or whether a development near a river flooding zone was given consent, have been made long before individuals move to a place that may be at risk of flooding, says Matthew Hughes, the engineer. The infrastructure that can determine the impact of flooding lasts far beyond a single term of council – and the rivers that flow over, under and around that infrastructure will endure even longer. Hughes points out that stormwater pipes and bridges built today will most likely endure for decades, possibly past the lifetime of the councillors, builders, and engineers who construct them, into a climate that is warmer, rainier, and more drought-prone.
Because of this, Hughes says it’s important for decision-makers – at Environment Canterbury or elsewhere – to consider what impact a policy or new development might have down the line. Ultimately, changing the relationships and societal structures, the context in which a flood occurs, may be the best protection. “We have to improve people and communities to withstand floods, create a society where having a highway blocked for a few weeks isn’t a complete disaster,” he says.
Cranwell agrees. “We need to work with communities to create that generational concept – to be thinking about 50 or 100 years,” he says. The council’s partnership with Ngāi Tahu is hopeful, and Environment Canterbury can use the perspective of mana whenua to make Canterbury better for awa and people alike. “We can allow those rivers to breathe again.”