Sediment and clarity

Sediment  is a natural component of any waterway system, it is any broken-down material that has made its way onto our waterways, It’s the natural by-product of hill country erosion, weather, the shifting of waterways, and the consequent erosion of stream banks.

However, sediment needs to be managed as excess amounts lead to:

  • Discoloured water that’s unattractive for swimming and recreation
  • Clogged river bed with less room for insect habitat and fish spawning
  • Reduced visibility for fish that need to see to catch food
  • Reduced in-stream vegetation
  • Clogged water supply intakes
  • Water that’s unpalatable to stock
  • Water requiring a higher standard of treatment before it’s suitable for human consumption
  • A reduced carrying capacity of lowland flood control schemes
  • Increase of other contaminants such as E. coli and phosphorus

Understanding sediment levels in the Manawatū Catchment and identifying areas that need attention can be achieved through monitoring of water clarity and turbidity. Water clarity is how clear the water is, while turbidity is how murky the water is. The level of cloudiness or haziness is caused by the amount of individual small particles suspended in the water. These indicators are monitored across the catchment. Find the most recent state and trends on the Land Air Water Aoteroa (LAWA) website.

In 2018 Accord member Horizons Regional Council commissioned Land Water People to conduct an independent region-wide review of water quality, download the full report with trend analysis here.

Te whakahaere waipara me te pūahoaho ā wai i te awa o Manawatū me ōna manga

Managing sediment and clarity in the Manawatū Catchment

Erosion can have a major impact on sediment and clarity in our awa. Many things can be done to manage this, such as:

  • Planting poplar and willow poles in erosion prone land. The root systems of these plants help to stabilise the land, reducing erosion and sediment run off from hills. The newly stabilised areas are also more sustainable for stock grazing and can be used as an emergency food supply during droughts.
  • Retiring land and regenerating native bush in erosion prone land that has a higher risk of sediment running off into waterways. Through fencing off this land, planting, and allowing bush to flourish, sediment in the awa is reduced and habitat is created for native plants and animals to thrive.
  • Planting riparian margins along our waterways. Riparian planting improves water quality, biodiversity and farming footprints in many ways. The root systems stabilise banks, reducing erosion and acting as a natural buffer that filters runoff and reduces sediment, E. coli and nutrients entering the water. As the plants grow they provide habitats for wildlife including birds and bees. The plants also create habitat for native fish by allowing undercuts to form under banks – creating hidey holes for fish to get away from predators. The plants create shade, which can lower water temperature and block sunlight, reducing the growth of algae and weeds and cooling and oxygenating streams which supports macroinvertebrates and other aquatic life.

One of the systems for applying these methods in the region is the Sustainable Land Use Initiative (SLUI). Led by Horizons Regional Council, with funding support from central government, this is the largest regional programme to address hill country erosion in New Zealand and involves working with landowners and other agencies to develop Whole Farm Plans. Through this programme farmers and landowners receive help to identify areas contributing sediment to waterways and expert advice and planning to reduce and mitigate this risk. Through monitoring, Horizons and Landcare Research have tracked the impact of the SLUI initiative. It has been modelled that even if work stopped in 2018, by 2043 the work already completed will lead to an 11 per cent reduction in annual sediment load in the Manawatū Catchment. The programme continues to grow as more and more landowners get on board. So far, 166 Whole Farm Plans have been developed in the Manawatū Catchment.

Visit the Horizons’ website to find out more about SLUI and getting a Whole Farm Plan and take a look at the See Progress Page to see what’s happening in your area.

Ngā Rangahau me ngā rauemi

Research and resources

Manawatū-Whanganui Regional water quality state and trends 2018
An independent region-wide review of water quality by Land Water People, commissioned by Accord member Horizons Regional Council, released in 2018.

Quantifying sediment sources of floodplain deposits in the lower Oroua River using sediment fingerprinting
This study investigated the application of a sediment fingerprinting technique to quantify sediment contributions from a range of sources in the lower Oroua River floodplain.

SedNetNZ, SLUI and contaminant generation Part 1: Sediment and water clarity
This report documents the use of sediment modelling using SedNetNZ in the Manawatū-Whanganui region. The report provides an assessment of the impact of soil conservation work to date (and possible future work under the Sustainable Land Use Initiative) on sediment loads and water clarity. An updated assessment of the impact of climate change on sediment loads is also provided.

SedNetNZ, SLUI and contaminant generation Part 2: Nitrogen, phosphorus and E. coli
This report applies the results of Part 1 of this study to assess the impact of the Sustainable Land Use Initiative (SLUI) on phosphorus (P), nitrogen (N) and E. coli loads in the region’s rivers.

GET INVOLVED

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FIND OUT HOW YOU CAN HELP

The Manawatū River is OURS and as a community we have the choice of playing a part in its enhancement and protection. Working together we can help our awa thrive and enjoy it today and for generations to come.

FIND OUT
HOW YOU CAN HELP

Slide Despite efforts to recycle, plastic waste ends up in our awa. Reduce the amount of unnecessary plastic you use to help reduce the amount of plastic waste produced locally.

REDUCE PLASTIC WASTE

REDUCE
PLASTIC WASTE

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PICK UP LITTER

Next time you’re down by the awa take on the challenge of picking up five pieces of litter. Every bit counts and it all adds up to a happier, healthier environment for everyone to enjoy.

PICK UP LITTER

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PLANT A TREE

The benefits of planting trees are many – for our awa they include filtering nutrients from land run off and providing habitat for birds, fish and insects.

PLANT A TREE

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DISPOSE OF TOXIC
CHEMICALS SAFELY

Stop hazardous waste from reaching the river by disposing of it at dedicated facilities. Remember that everything that goes down the drain will eventually end up in our rivers and streams.

DISPOSE OF TOXIC
CHEMICALS SAFELY

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SEE IT, REPORT IT,
CALL 0508 800 800

If you see a chemical spill or contaminants in waterways call Horizons’ Pollution Hotline.

SEE IT, REPORT IT,
CALL 0508 800 800

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WASH YOUR CAR
ON THE GRASS

Grass acts as a natural filter for contaminants, trapping potential pollutants such as oil, dirt and grease. Washing your car on the lawn filters run off through the soil before entering stormwater drains and ultimately the river.

WASH YOUR CAR
ON THE GRASS

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JOIN THE CONVERSATION

Join the conversation and get involved, there are a lot of things you can do to help and we have the resources to show you how. Join our community on social and find out more at manawaturiver.co.nz

JOIN THE CONVERSATION

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Find out what you can do

The Manawatū River is OURS and as a community we have the choice of playing a part in its enhancement and protection. There is a lot you can do to help our awa thrive, and we are here to help you make a difference.

Find out what you can do

Slide Erosion can have a major impact on sediment and clarity in our waterways. Reduce the amount of sediment entering our awa and keep soil on your land by planting poplar poles in erosion prone areas.

COMBAT HILL COUNTRY EROSION

COMBAT HILL COUNTRY EROSION

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FIX BARRIERS TO FISH PASSAGE

Many of the native fish species need to get back and forth between their fresh water homes and the sea to breed. Barriers to this migration seriously impact our native fish, many of which are at risk. Find out how to make dams, weirs, and overhanging culverts in your streams fish friendly.

FIX BARRIERS TO FISH PASSAGE

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PROTECT STREAMS WITH RIPARIAN PLANTING AND FENCING

Keeping stock out of waterways and protecting streams with a buffer of plants along stream margins has a major impact on water quality and stream habitat. Improve sediment, nutrient, and bacteria levels in our awa and help aquatic life thrive in your streams through effective riparian management.

PROTECT STREAMS WITH RIPARIAN PLANTING AND FENCING

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MANAGE EFFLUENT ON YOUR FARM

Nutrient and bacteria in our waterways has a major impact on water quality in our catchment. Implement sustainable systems for managing effluent on your farm and help keep our awa healthy and safe.

MANAGE EFFLUENT ON YOUR FARM

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PROTECT WETLANDS AND NATIVE BUSH ON YOUR LAND

Today only 18 per cent of the catchment remains under indigenous cover. There are many programmes in the catchment working to protect these precious ecosystems. Find out how to protect bush remnants and wetlands on your land.

PROTECT WETLANDS AND NATIVE BUSH ON YOUR LAND

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LEAD A COMMUNITY PROJECT

Every year there is $100,000 of funding for community projects that aim to enhance and protect the awa. Take advantage of the support available and galvanise your community to protect our waterways.

LEAD A COMMUNITY PROJECT

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JOIN THE CONVERSATION

Join the conversation and get involved, there are a lot of things you can do to help and we have the resources to show you how. Join our community on social and find out more at manawaturiver.co.nz

JOIN THE CONVERSATION