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Human activities

Human activities create a raft of problems for braided rivers, from deliberately introduced predators and invasive plants to climate change. These are historic and/or large scale problems that require complex management strategies.

This page outlines current and future problems caused by recreational and commercial activities, all of which can be addressed through advocacy, community education, and legislation. Some but not all of these issues are being discussed and decided upon through thCanterbury Water Management Strategy.

Pollution

Pollution comes from point and non-point sources. Point sources include things like industrial discharges and sewerage treatment plants and urban runoff through drains. Non-point sources are harder to define, and include farm and urban runoff over the land and through soils. In Canterbury, farm runoff is a major problem, particularly with the recent rapid growth in dairy farming and irrigation adding excess nitrogen and phosphate to the waters, along with agricultural chemicals and heavy metals such as cadmium. Excess nitrogen combined with phosphate, for example, leads to algae blooms. This reduces oxygen in the water and the amount of light getting through, starving native plants and destroying in-stream invertebrate and fish habitats. At the top of the food chain, there is less or no food for river birds.

Water abstraction

We take a great deal of water from our rivers, for domestic use, manufacturing and other commercial reasons, to generate power, and for irrigation. Taking water from braided rivers changes their natural character and hydrology. When water levels drop, the gravel islands used by many birds to nest become joined to the land. Introduced predators including hedgehogscats and stoats are then easily able to reach nests. They steal eggs, kill chicks and nesting parents, and often scare away entire colonies of rare and endangered breeding birds. Low levels of water also means pollution becomes more concentrated. This is a critical problem in Canterbury, which has a naturally drier climate that other parts of the country, a situation that will be increasing challenging as the effects of climate change accelerate.

Economy vs Ecology

This alarming report from ECan shows that from 1990-2012, over 11,000 hectares of braided rivers were converted to intensive agriculture. A discussion of the impacts of intensive dairy farming and concurrent water abstraction and pollution in Canterbury, and the ongoing legal arguments regarding ecology vs economy, can be found here: ‘Rivers of Gold‘.

Centre pivot irrigation in the historic riverbed of the Waiau River

Centre pivot irrigation in a section of what was the the historic riverbed of the Waiau River.

Engineering works

Work in riverbeds is done for many reasons, including flood control, road and bridge construction, gravel extraction, land development, and water storage and diversion. These activities can interfere with the natural character of braided rivers, in turn affecting braided river birds. For example, machinery in riverbeds during the breeding season may disturb breeding birds and destroy nests, killing eggs and chicks. Poorly managed gravel extraction and water storage may change the hydrology of the river so that it is no longer ‘braided’. In the worst cases, poorly managed gravel extraction can exacerbate erosion and flooding, cause sediment to enter waterways, leading to the degradation or destruction of ecosystems.

In contrast, well-managed riverbed works such as gravel extraction can help restore the character of rivers by removing invasive weeds, helping to create and maintain islands, and keeping waterways flowing even during minimal flow periods. Timing is often everything. In many instances it’s simply a case of avoiding a very small patch of rivers where birds nest during the breeding season. Under the Braided Rivers Partnership Project, BRaid is working with gravel extractors such as Taggarts and Fulton-Hogan who are actively assisting to create and restore braided river bird habitats as part of their day-to-day operations.

Irresponsible gravel extraction in the Ashley-Rakahuri catchment

Irresponsible gravel extraction destroys the natural character or rivers and allows sediment to enter waterways.

Recreational activities

Unattended eggs and young chicks are extremely vulnerable to predation and cold temperatures. If parent birds are kept away from their nests, the eggs and young chicks quickly perish. People, and their dogs, commonly disturb nesting birds. Vehicles can run over eggs and chicks. The wash from speeding jetboats can erode banks, flood nests, kill chicks and disrupt feeding. In 2013, Samuel John Townhill pleaded guilty to Department of Conservation charges of destroying nests and disturbing a protected species when he drove into a 3000-strong black-billed gull colony on the Ashburton Hakatere. He was sentenced to one month’s imprisonment. In 2014 a single fishermen caused an entire colony of birds to abandon their nests in the Ashley Rakahuri. Microlight aircraft and kitesurfing around areas where birds breed can also disturb them. 

There are very few remaining places where rare and endangered birds nest along our braided rivers. In contrast, there are many many places where we can  walk dogs, drive off road vehicles, go fishing and kite-surfing, drive our boats and fly our planes. For the most part, when people learn how precious these small sections of rivers are to area and endangered birds, they celebrate their arrival and are either careful not to interfere or actively help to protect these areas. Unfortunately, some recreational users either ignorantly or purposefully set out to destroy these precious few remaining areas.

Driving through rivers can devastate nesting birds

Driving through rivers can devastate nesting birds

Black-fronted tern chick crushed by 4-wheel driver

Black-fronted tern chick crushed by 4-wheel driver.

Waipara river mouth 4X4 attack on sign

A 4X4 attack on an information sign explaining the nesting birds and important Maori cultural values of the Waipara River.

Conservation activities

  •  Key targets for the Canterbury Water Management Strategy Chapter 3: Natural character of braided rivers

    • Maintain the upper catchments of alpine braided rivers as largely natural ecosystems and landscapes
    • No new dams on the main-stem of major alpine braided rivers
    • Maintain active floodplains, flow variability and sediment movement – including during river protection works, land-use change or deliberate vegetation stabilisation
    • Support the dynamics of river mouth and coastal processes
    • Implement actions to correct the decline in useable braided river bird habitat
  • BRaid actively supports and advises recreational and commercial users through a range of strategies outlined here.

More information

 

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