Te Mana o Te Wai Tairawhiti

Earlier this month many of the country’s top freshwater scientists, advocates and thinkers assembled in Uawa/Tolaga Bay for Te Mana o Te Wai Tairawhiti freshwater symposium. Michael Neilson went along to learn about the key challenges facing Tairawhiti, and where to from here.

Earlier this month many of the country’s top freshwater scientists, advocates and thinkers assembled in Uawa/Tolaga Bay for Te Mana o Te Wai Tairawhiti freshwater symposium. Michael Neilson went along to learn about the key challenges facing Tairawhiti, and where to from here.

LET'S TALK ABOUT TE WAI: Dr Wayne Ngata (Te Aitanga a Hauiti) explains to a group at Te Mana o Te Wai freshwater symposium some of the challenges they face in Uawa/Tolaga Bay. Like many rivers and streams in Tairawhiti erosion and sedimentation are their biggest issues. Picture by Michael Neilson
RIVER MOVEMENT: Dr Jon Tunnicliffe (left), a lecturer in river geomorphology at the University of Auckland, has been studying the Waiapu River catchment with PHD candidate Gabriel Spreitzer.
MORE TREES: Dr Mike Marden of Landcare Research has long been involved in researching erosion issues and solutions in Tairawhiti. "The bottom line though is we need more trees," he says. Picture by Paul Rickard

TUATAHI ko te wai, tuarua whanau mai te tamaiti, ka puta ko te whenua — when a child is born the water comes first, then the child, followed by the afterbirth (land).”

This whakatauki showed the importance of clean, healthy water, said Tolaga Bay Area School student Sue-Anne Albert-Hovell.

She was speaking at Te Mana o Te Wai Tairawhiti, a symposium held earlier this month in Uawa/Tolaga Bay about freshwater issues in the region.

Forestry wood, siltation and run-off from farming were all impacting their awa, so too climate change, which was reducing Ranginui’s (sky father) tears and harming Papatuanuku (earth mother).

“Healthy seas and rivers mean a healthy community, which for us means keeping our culture alive.”

New Zealanders have long-prided themselves on pristine swimming holes, being able to take a gulp of water from back-country streams, or fish in crystal clear rivers.

Yet in recent years, many waterways around the country have reached near-breaking point, whether as a result of intensive farming, poor urban wastewater management, or more natural events like storm-induced erosion.

During the symposium it was clear from the expert presentations Tairawhiti’s waterways have long had one main adversary — erosion.

Fresh water and sedimentation

Palmerston North-based Massey University freshwater ecology professor Dr Russell Death has long hammered his local council over freshwater issues, including sedimentation.

“I used to think we had bad erosion in the Manawatu,” he said. “But after visiting Tairawhiti, I realise how lucky we are.”

Dr Death has a simple test to check if there is too much sediment in a waterway (too much as in degrading its life-supporting capacity). It involves shuffling one’s feet along the riverbed. If the water turns murky, there is too much silt.

In Tairawhiti one would be lucky to find a river that was not murky to begin with. Silt-laden rivers are not only unpleasant to swim in but they affect life in the water, and mauri, by smothering animals and invertebrates.

“Good ecology is not just about having clean water, or a good amount,” Dr Death said.

“We also need good habitats.”

The Waipaoa catchment, fed by the infamous Tarndale and Mangatu slips, pumps out 15 million tonnes of suspended sediment, including fine soil, silts and clays, into the sea every year.

There are anecdotes of swimming holes being filled in, declining fish stocks, and even a buried marae in Whatatutu.

Waiapu sacred to Ngati Porou

Then there is the mighty Waiapu, sacred to Ngati Porou. That river catchment is estimated to produce a whopping 35 million tonnes of sediment — 17 percent of the volume from all New Zealand rivers from 0.6 percent of the land area.

The buried Raparapariki bridge knows this all too well, as does another section where sediment has piled 30 metres high.

Gisborne city’s three rivers, the Waimata, Taruheru and Turanganui, treasured by many for swimming and watersports, including waka ama, are all murky with silt.

They are becoming increasingly shallow from the sediment, raising the risk of flooding and creating issues at the port, which has to dredge it out of the harbour.

But if one dug deep enough (some very deep) in these rivers they would find the stony creek and river beds that once covered the region.

The district’s sediment-choked rivers are the subject of many research projects — both current and future.

Dr Ian Fuller, a physical geography lecturer at Massey University, has done much research in the Waipaoa catchment understanding sediment pathways, including production areas, chutes and depositing areas.

Dr Jon Tunnicliffe, a lecturer in river geomorphology at the University of Auckland, studied the region’s geology in his undergraduate days in his native Canada.

Tairawhiti’s rivers and their erosion issues were “world famous”, Dr Tunnicliffe said.

For the past four years his focus has been on the Waiapu River.

With a team of undergraduates they have been working on a sediment budget for the Mata River (a tributary to the Waiapu) in order to assess how much material was coming out of the gullies and how much was being recruited into the river system.

Laser scanning

They have been using LiDAR (laser scanning) and drone-based photogrammetry techniques. Contrasting modern images with a database of aerial photos stretching back to 1939, they are able to see how the catchment has changed.

In the long-term this research will assist with developing a strategic framework for targeted interventions to manage the river catchment.

One of the team members, Gabriel Spreitzer (of Austria), will be undertaking his PhD looking at forestry slash management in Tairawhiti.

He is keen to investigate the movement of woody debris, where it comes from, where it goes and where it accumulates.

Dr Mike Marden of Landcare Research has long been involved in researching erosion issues and solutions in Tairawhiti.

He showed the audience an image of a rocky, boulder-laden river, with lush native forest around it and clear water flowing through it.

“This is how the rivers here used to be,” Dr Marden said. “We went from boulder-armoured streams before deforestation, to wider silt-laden rivers.”

Between the 1880s and 1920s the vast majority of native vegetation was removed from the region, either by logging or burning it down, as humans transformed the bush into grassy pasture to raise stock.

“Within a decade there were warning signs that it was not a good decision,” Dr Marden said.

Land slipping into sea

The land began slipping into the sea and, while it had always done so, this was something new.

“Tairawhiti’s erosion problems are highly complex,” said Dr Marden.

They are a combination of difficult geology and terrain.

The relatively young land and soft rock, thrust up from the sea-floor in steep slopes, is highly-erodible.

When it rains heavily, as it is accustomed to do in this region, the moisture either washes the soft rock off the slopes, or it soaks into the ground, saturating the soil and causing landslides.

Erosion is not only bad for waterways, but the loss of topsoil is a loss of natural capital, which reduces the productive capacity of the land in the future.

To produce a single centimetre of topsoil in nature can take several hundred years, and thousands of years to develop enough soil to form productive land. But that can be lost during a single storm.

As land is eroded its productivity declines over time.

Dr Marden said retaining areas of indigenous forest and reforesting areas with exotics, such as pine, poplar and willow would help solve the problem.

“It does not matter what species. Any tree is a good tree for controlling erosion.”

With forest cover the amount of rain hitting the ground and soaking into it is diminished.

Green canopy intercepts rainfall

Dr Marden estimates an evergreen canopy intercepts 30 percent of rainfall, which evaporates back into the atmosphere.

Of the remaining 70 percent another 30 percent is extracted through the tree roots.

Soils under a closed-canopy forest cover remain drier for longer and are less likely to fail.

In the 1960s the Government and local authorities began afforestation projects in erosion-prone areas — mostly with pine — and then again in the 1990s following Cyclone Bola.

Now the harvesting of many of these areas is heralding another change.

Following harvesting it takes six to eight years for new trees to hold the land.

If there is a major storm in that time it can lead to landslides and sediment being washed into waterways.

“In this region’s climate it is inevitable that at times harvesting will coincide with storm events,” Dr Marden said.

He believes forestry on steep terrain might not be sustainable in the long-term.

“We need a re-evaluation of current land uses in the region, not just forestry, but also where there are pastoral farms on steep hill country that is prone to erosion.”

Targeted tree planting

This land-use change would involve more targeted tree-planting, particularly of gullies.

In the Waipaoa catchment, gullies contribute 43 percent of the total sediment lost, and in the Waiapu 50 percent.

A Landcare Research modelling exercise found that if trees had been planted in all of the district’s gullies by 2008 this alone could have halved the sediment loss by 2050.

Their research has also found that water quality and stream health in mature pine forests in soft rock terrain was similar to that under native forests.

However, indigenous species as riparian plantings also play a crucial role in improving stream health, and in some areas may be more appropriate than exotics.

“The bottom line though is we need more trees, not fewer, and it is inevitable that the most vulnerable parts of this landscape will need to go into forests,” Dr Marden said.

TUATAHI ko te wai, tuarua whanau mai te tamaiti, ka puta ko te whenua — when a child is born the water comes first, then the child, followed by the afterbirth (land).”

This whakatauki showed the importance of clean, healthy water, said Tolaga Bay Area School student Sue-Anne Albert-Hovell.

She was speaking at Te Mana o Te Wai Tairawhiti, a symposium held earlier this month in Uawa/Tolaga Bay about freshwater issues in the region.

Forestry wood, siltation and run-off from farming were all impacting their awa, so too climate change, which was reducing Ranginui’s (sky father) tears and harming Papatuanuku (earth mother).

“Healthy seas and rivers mean a healthy community, which for us means keeping our culture alive.”

New Zealanders have long-prided themselves on pristine swimming holes, being able to take a gulp of water from back-country streams, or fish in crystal clear rivers.

Yet in recent years, many waterways around the country have reached near-breaking point, whether as a result of intensive farming, poor urban wastewater management, or more natural events like storm-induced erosion.

During the symposium it was clear from the expert presentations Tairawhiti’s waterways have long had one main adversary — erosion.

Fresh water and sedimentation

Palmerston North-based Massey University freshwater ecology professor Dr Russell Death has long hammered his local council over freshwater issues, including sedimentation.

“I used to think we had bad erosion in the Manawatu,” he said. “But after visiting Tairawhiti, I realise how lucky we are.”

Dr Death has a simple test to check if there is too much sediment in a waterway (too much as in degrading its life-supporting capacity). It involves shuffling one’s feet along the riverbed. If the water turns murky, there is too much silt.

In Tairawhiti one would be lucky to find a river that was not murky to begin with. Silt-laden rivers are not only unpleasant to swim in but they affect life in the water, and mauri, by smothering animals and invertebrates.

“Good ecology is not just about having clean water, or a good amount,” Dr Death said.

“We also need good habitats.”

The Waipaoa catchment, fed by the infamous Tarndale and Mangatu slips, pumps out 15 million tonnes of suspended sediment, including fine soil, silts and clays, into the sea every year.

There are anecdotes of swimming holes being filled in, declining fish stocks, and even a buried marae in Whatatutu.

Waiapu sacred to Ngati Porou

Then there is the mighty Waiapu, sacred to Ngati Porou. That river catchment is estimated to produce a whopping 35 million tonnes of sediment — 17 percent of the volume from all New Zealand rivers from 0.6 percent of the land area.

The buried Raparapariki bridge knows this all too well, as does another section where sediment has piled 30 metres high.

Gisborne city’s three rivers, the Waimata, Taruheru and Turanganui, treasured by many for swimming and watersports, including waka ama, are all murky with silt.

They are becoming increasingly shallow from the sediment, raising the risk of flooding and creating issues at the port, which has to dredge it out of the harbour.

But if one dug deep enough (some very deep) in these rivers they would find the stony creek and river beds that once covered the region.

The district’s sediment-choked rivers are the subject of many research projects — both current and future.

Dr Ian Fuller, a physical geography lecturer at Massey University, has done much research in the Waipaoa catchment understanding sediment pathways, including production areas, chutes and depositing areas.

Dr Jon Tunnicliffe, a lecturer in river geomorphology at the University of Auckland, studied the region’s geology in his undergraduate days in his native Canada.

Tairawhiti’s rivers and their erosion issues were “world famous”, Dr Tunnicliffe said.

For the past four years his focus has been on the Waiapu River.

With a team of undergraduates they have been working on a sediment budget for the Mata River (a tributary to the Waiapu) in order to assess how much material was coming out of the gullies and how much was being recruited into the river system.

Laser scanning

They have been using LiDAR (laser scanning) and drone-based photogrammetry techniques. Contrasting modern images with a database of aerial photos stretching back to 1939, they are able to see how the catchment has changed.

In the long-term this research will assist with developing a strategic framework for targeted interventions to manage the river catchment.

One of the team members, Gabriel Spreitzer (of Austria), will be undertaking his PhD looking at forestry slash management in Tairawhiti.

He is keen to investigate the movement of woody debris, where it comes from, where it goes and where it accumulates.

Dr Mike Marden of Landcare Research has long been involved in researching erosion issues and solutions in Tairawhiti.

He showed the audience an image of a rocky, boulder-laden river, with lush native forest around it and clear water flowing through it.

“This is how the rivers here used to be,” Dr Marden said. “We went from boulder-armoured streams before deforestation, to wider silt-laden rivers.”

Between the 1880s and 1920s the vast majority of native vegetation was removed from the region, either by logging or burning it down, as humans transformed the bush into grassy pasture to raise stock.

“Within a decade there were warning signs that it was not a good decision,” Dr Marden said.

Land slipping into sea

The land began slipping into the sea and, while it had always done so, this was something new.

“Tairawhiti’s erosion problems are highly complex,” said Dr Marden.

They are a combination of difficult geology and terrain.

The relatively young land and soft rock, thrust up from the sea-floor in steep slopes, is highly-erodible.

When it rains heavily, as it is accustomed to do in this region, the moisture either washes the soft rock off the slopes, or it soaks into the ground, saturating the soil and causing landslides.

Erosion is not only bad for waterways, but the loss of topsoil is a loss of natural capital, which reduces the productive capacity of the land in the future.

To produce a single centimetre of topsoil in nature can take several hundred years, and thousands of years to develop enough soil to form productive land. But that can be lost during a single storm.

As land is eroded its productivity declines over time.

Dr Marden said retaining areas of indigenous forest and reforesting areas with exotics, such as pine, poplar and willow would help solve the problem.

“It does not matter what species. Any tree is a good tree for controlling erosion.”

With forest cover the amount of rain hitting the ground and soaking into it is diminished.

Green canopy intercepts rainfall

Dr Marden estimates an evergreen canopy intercepts 30 percent of rainfall, which evaporates back into the atmosphere.

Of the remaining 70 percent another 30 percent is extracted through the tree roots.

Soils under a closed-canopy forest cover remain drier for longer and are less likely to fail.

In the 1960s the Government and local authorities began afforestation projects in erosion-prone areas — mostly with pine — and then again in the 1990s following Cyclone Bola.

Now the harvesting of many of these areas is heralding another change.

Following harvesting it takes six to eight years for new trees to hold the land.

If there is a major storm in that time it can lead to landslides and sediment being washed into waterways.

“In this region’s climate it is inevitable that at times harvesting will coincide with storm events,” Dr Marden said.

He believes forestry on steep terrain might not be sustainable in the long-term.

“We need a re-evaluation of current land uses in the region, not just forestry, but also where there are pastoral farms on steep hill country that is prone to erosion.”

Targeted tree planting

This land-use change would involve more targeted tree-planting, particularly of gullies.

In the Waipaoa catchment, gullies contribute 43 percent of the total sediment lost, and in the Waiapu 50 percent.

A Landcare Research modelling exercise found that if trees had been planted in all of the district’s gullies by 2008 this alone could have halved the sediment loss by 2050.

Their research has also found that water quality and stream health in mature pine forests in soft rock terrain was similar to that under native forests.

However, indigenous species as riparian plantings also play a crucial role in improving stream health, and in some areas may be more appropriate than exotics.

“The bottom line though is we need more trees, not fewer, and it is inevitable that the most vulnerable parts of this landscape will need to go into forests,” Dr Marden said.

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