Photos: Nick Ledgard
Ashley Rakahuri River: May 2021
Left: 4.00pm 29 May. Water flow 4 cumecs.
Right: 4.00pm 30 May. Water flow 966 cumecs.
By definition, braided rivers are made up of multiple channels or ‘braids’. Systematically forcing them into the solitary confinement of single channels is turning them into what University of Waikato’s Professor James Brasington calls “zombie” rivers, waterways locked into position between stopbanks and their headwaters. Planting willows and poplars as a ‘natural’ way to hold them in place has just exacerbated the problem. Confining braided rivers not only creates problems for freshwater ecosystems including habitat for braided river birds, it also makes these rivers prone to catastrophic flooding.
“If we put our rivers into straight-jackets, they lose the diversity of form and process that are fundamental to the creation of thriving ecosystems. Instead, we should make space for rivers to erode their corridors, flood naturally in areas that are of less value which will in turn, reduce risks in more sensitive areas. We must work with natural processes to reduce the flood risk and support healthy river ecosystems.” – James Brassington
Last weekend, several zombie rivers in Canterbury broke free and invaded towns and properties.
It’s not like we weren’t warned. In 2019, NIWA published this extraordinarily well-ignored report outlining the current NZ$40 billion flood risks to Canterbury (no, that’s no a misprint; it’s billion, not million) (Fig. 2) .
I’ve yet to meet anyone who read their entire report, much less acted on it. A small extract made headline news in a North Canterbury paper and was promptly forgotten.
Two weeks ago, I gave a presentation to the Waimakariri drainage group on the risks of flooding from pluvial and fluvial events and rising sea levels. It caused some discomfort, but then again, I was talking about climate change. A concept that probably seemed too remote to lose much sleep over.
Last weekend’s floods will no doubt make headline news again in our local papers. And in a few weeks it will also probably be forgotten by most people, especially those who weren’t directly affected. Part of the reason is that the phrase ‘1-in-100 event’ is often misunderstood, leading to a false sense of security that these zombies and their big brother rivers are unlikely to escape again in our lifetimes. (The term ‘1-in-100 years’ is in fact a statistical annual exceedance probability. It’s arguably moot in any case as many hydrologists consider stationarity to be dead.)
And then there’s the false perception that ECan is obligated to shove every metre of rivers back into solitary confinement. The situation on the Okuku River is a case in point. The poor little Okuku, like many zombie rivers, is so glutted with weeds that it’s unrecognisable as a braided river. We don’t even include it on this website. I mention it here now, because this section of the Okuku is outside the river ratings area. So no, councils are under no obligation to protect those who choose to live and farm in its riverbed. And that’s costing all of us as insurance premiums are bound to hike up a notch.
In January this year, nine New Zealand river experts wrote an article in The Conversation, titled ‘Why we should release New Zealand’s strangled rivers to lessen the impact of future floods’. I had included this in the ‘News’ section below when I was drafting this newsletter last Friday. Subsequent events dictate it’s worth posting some of the content here:
“We shouldn’t be surprised when our rivers break their banks — that’s just a river being a river. Current management practices in Aotearoa treat rivers as static, in the hope of making them more predictable.
“But this can lead to disasters.
“Unless we change management practices to work with a river, giving it space to move and allowing channels to adjust, we will continue to put people and rivers on a collision course.
“When flood risk is managed poorly, disadvantaged groups of the population are often disproportionately impacted. Given climate change predictions of more extreme floods and drought, the problem will only get worse.”
- Why we should release New Zealand’s strangled rivers to lessen the impact of future floods (The Conversation)
- Vested Interests: a freshwater scientist’s personal experience, by Mike Joy (Policy Quarterly)
- There are 50 billion wild birds on Earth – but four species dominate (New Scientist)
- Pivotal problem: Drive for irrigation efficiency backfires for environment (Newsroom)
- The Waikirikiri / Selwyn Near River Recharge project (ECan)
- Selwyn council not kitten around: all cats in district must be microchipped (Stuff)
- Four NZ documentary films Fight for the Wild (Radio NZ) available to see free of charge, online now.
- UN report: State of Finance for Nature; This year’s report calls for investments in nature-based solutions to triple by 2030 and to increase four-fold by 2050 from the current level.
- Breeding wrybills face multiple challenges; Kate Guthrie at Predator Free NZ has written this great article on the research paper by John Dowding, Elaine Murphy and Mike Elliott that was in the last BRaid newsletter.
- The Future Shape of Water, Water And Atmosphere, NIWA
- Rivers can be climate change solutions, too, Stuff April 12
- Great photo of variable oystercatchers from Darren Markin; not often 2 pure colours like these seen together
- Another great photo, this one of black-fronted terns bringing skinks, by Glenda Rees.
- Collaborative Research Agreement with DOC for Studies on the South Island Pied Oystercatcher
- NIWA: New Zealand Fluvial and Pluvial Flood Exposure
- Ministry for the Environment: Issue 4: Climate change is affecting freshwater in Aotearoa New Zealand
- Canning et al; Nutrient criteria to achieve New Zealand’s riverine macroinvertebrate targets, Aquatic Biology May 31
- Jane et al; Widespread deoxygenation of temperate lakes, Nature 594, pp66–70
- Pascolinni-Campbell et al; A 10 per cent increase in global land evapotranspiration from 2003 to 2019, Nature 593, pp543–547
- Pierce; When the levees break, Science 14 | 372, Issue 6543 pp676-679
- Valenza et al; Downstream changes in river avulsion style are related to channel morphology, Nature Communications 11 | 2116
- Musselman et al, Winter melt trends portend widespread declines in snow water resources, Nature Climate Change 11, pp418–424