Scholarship winner Jacob Robinson to study Whanganui River

Jacob Robinson studies the silt that comes down the Whanganui River - and would like to see it reduced. Photo / Bevan Conley

Jacob Robinson doesn't want to study mud all his life - but he'd like to contribute to lessening the mud coming down the Whanganui.

He's twice won a scholarship for his earth science studies from Whanganui organisation Te Mana o Te Awa. The latest one is $10,000 - and a lot of it will be used to buy petrol for his jetboat, as he takes samples of river mud from tributaries unreachable by car.

The geochemistry of the samples is analysed by a $1 million machine at Massey University, and he's finding enough differences in the mud samples to tell them apart. It's all part of his effort to understand why there is so much silt clogging the river, where it comes from and what the river was like before it.

He's conducting this study through the lens of mātauranga Māori, Māori knowledge.

"Our iwi has been living on that river for 700 years or longer. Within that time period we have just been learning about the river the whole time," he said.

The river washes about four million tonnes of soil into the sea every year.

"It's been flushing fertile soils out to sea for 150 years now, so some of those hills are looking pretty bony these days."

Its sediment load is the Whanganui's biggest environmental problem. The main way of measuring it is simply to look at the water through a tube and find out how far you can see.

Robinson hopes to find out what the river was like before bush was felled for farmland, a time when stones could be pulled out of the riverbed downstream from the city.

"Most of [that stone] is probably still under there. I want to see if it's still there."

The silt choking the river has completely changed it, he said - the life in it, they way it moves, the way it floods.

Forest used to keep topsoil on the hills, and these days the bush upriver is not being indiscriminately felled.

"You would think that things would be starting to improve, but they don't really seem to be. That could be because of climate change, and more intense rainstorms."

Steps to reducing the river's silt load would be: first to improve the health of the forest that still exists, and second to plant marginal land back into forest.

Robinson has always been interested in the earth and earthquakes, volcanoes and erosion. But for him going to university was "an outrageous dream".

"My family and most of my friends had never been to university."

He did a three-year degree in earth science at Massey, followed by two years of honours study with Mt Ruapehu's lahar history as his topic. Now he's in the final two years of writing his PhD thesis on Whanganui River silt, and said the scholarship money is essential to finishing the project.

Without it he would have to have chosen an easier river, one where he could get to tributaries and take samples by travelling in a car. It wasn't what he wanted.

"I'm just trying to learn all I can about my own backyard. After that I intend to work in my own backyard," he said.