Braided rivers are unique due to their shifting channels and banks, varying flows, ability to move over the landscape, and ecosystems. Because of this, they provide an outstanding habitat for many rare birds, fish, plants and other species.
The movement of gravels, working and reworking of sediments to form islands, plains, river mouths and coastal beaches, all contribute to sustaining the mauri (life force) of braided river systems.
Over time, and with historical use and development, some of the ecological and biodiversity values of these special rivers have deteriorated.
Canterbury’s braided rivers also provide much of the water to precious groundwater aquifers. Originating in the Southern Alps, these river systems cross the porous soils of the Canterbury Plains, losing water to ground and feeding aquifers deep under the land.
Aquifers provide our fresh drinking water and the vast amounts of water needed to sustain our population and our economy, while surface water is still king when it comes to irrigation.
Long before braided rivers were kāinga mahinga kai/food gathering habitat for Māori, a water supply for farmers and a recreational hotspot for the half-million people living nearby, they were quite literally world builders.
For thousands of years, mighty ice-age glaciers carved through the Southern Alps, pulling loose rock and sediment from headwaters and sending them forth in a great alluvial wash from the mountains to the sea.
Loads were deposited in such quantities that the coastline was driven east and New Zealand’s largest area of flat land, the Canterbury Plains, was created.
What can I do to help protect these species?
Environment Canterbury principal biodiversity advisor, Dr Frances Schmechel, said we all have a role to play in sharing the environment and protecting these precious rare birds.
“During the breeding season from September to the end of January, keep your dogs on a leash, as chicks can be swallowed before owners have a chance to call the dog back,” Frances said.
“Birds are hard to spot, but if you do see them, give them plenty of space. If they appear agitated, start flying, dive-bomb or hover over you, you’re much too close and may even be standing on their nest.
“Stay on formed tracks and observe signs – many nests with eggs or chicks have been crushed by vehicles because of their camouflage from aerial predators,” she said.
Giving threatened species a helping hand
In 2018-19 Environment Canterbury began black-backed gull/karoro control on several braided rivers. Black-backed gull once co-existed with other endemic braided river birds, but in much lower numbers than are present today.
Numbers have increased markedly recently and there are now large colonies on braided river beds, crowding out other species and creating E. coli problems in the rivers.
In contrast, Frances said, populations of black-fronted tern, banded dotterel, wrybill and black-billed gull have declined in that time, in part due to predation by the larger black-backed gulls.
“Karoro (black-backed gull) can harass colonies of threatened native birds until the entire colony fails. They can swoop in and devour small chicks whole in just seconds,” she said.
In addition to black-backed gull, pest control operations are carried out for a range of pests including hedgehogs, wild cats, stoats, weasels, ferrets and rats.
“This control, which is mostly trapping, is carried out by community groups and contractors on various rivers. Without it, our precious braided river birds would have even less chance of breeding successfully,” Frances said.
Braided river mouths are particularly important for Ngāi Tahu, providing an important habitat for many species.
They are also important in the coastal gravel nourishment process. The beds and margins of lakes and rivers are part of the waterbody, and not separate from it.
Environment Canterbury Tangata Whenua facilitator, Irai Weepu, said this concept is captured in the phrase ‘ki uta ki tai’ (from the mountains to the sea), the holistic view of the catchment as one system.
“This is also integrated with kaitiakitanga from Ngāi Tahu which applies to the ecological health and overall wellbeing of all waterways,” Irai said.
Tuna/eels and inanga/whitebait are taonga species for Ngāi Tahu because of their importance in mahinga kai/food and resource gathering.
Healthy waterway challenges
But for the past 120 years, the relationship between Māori and braided rivers has not been a happy one due to the declining number of healthy waterways.
“In the past, every part of the river was pristine and drinkable, every part was abundant with life. Native plants and animals could be sustainably harvested,” Irai said.
“Rivers were full of water and free to flow their natural paths. Now the water is polluted and not always drinkable, and sometimes not swimmable.
“Biodiversity has decreased and plants and animals are most often either absent or too polluted to be harvested. The rivers in some parts are almost empty of water and constrained. The future is getting back what was lost,” he said.
Food from the rivers, particularly tuna and inanga, were lifelines which have gradually been cut-off by land conversion and mistreatment over a number of generations.
Strict rules are now in place to ensure farmers measure and manage the effects of their farming on local water quality. Controls have been placed on land-use activities that could threaten water quality.
In Canterbury we have some of the strictest farming rules in the country. Farmers must operate within limits and adhere to industry-agreed Good Management Practices (GMPs).
The goal is to halt the decline of braided rivers, focusing on goals and targets in integration of water and land management, including protecting biodiversity and water quality.
Benefits from this funding
Environment Canterbury Councillor, John Sunckell, said the funding aids the important Canterbury braided rivers, the need to protect them, and those who live near them.
“Five of the projects are on Canterbury’s braided rivers, which are taonga and highly valued by Ngāi Tahu. They are stunning landscapes, with high natural and cultural values," he said.
"This funding allows us to simultaneously care for braided rivers as the special places they are, while keeping our community safe with key infrastructure projects.”