Taniwha in the valley: Hutt River is both threatened and threatening - but is it just misunderstood?

Thursday, 22 April 2021

The Hutt River gets a health check every week, monitoring for E.coli, toxic algae and nutrients (first published April 2021)

A person can survive three weeks without food, but only three days without water. With climate change a looming certainty, there will be nothing more crucial to our survival. But the source of our water is increasingly tainted. In the first of a series on the Wellington region’s waterways, Kate Green reports on the health of Hutt River.

Māori wisdom likens a river to a taniwha’s tail. It whips side to side, changing its course on a whim, unpredictable – you don’t want to get too close.

But civilization had other plans for the Hutt River. Where it passes through the Hutt Valley, houses crowd it on either side, recreation spots are carved into its banks, and its health varies from inlet to inlet.

Also called Te Awakairangi – awa meaning river, kairangi meaning held in high esteem – it hosts more than one million visitors each year who walk, run, cycle, picnic, fish, and swim, but it’s plagued by issues from flooding to E.coli, sediment to toxic algae.

* Caution remains after algal blooms found in two North Canterbury rivers

Surrounded by civilisation, the Hutt River is often the final destination for contaminants washing off pavements and down drains from the city. (File photo)

* Melling interchange designs for Hutt Valley choke point put to the people

* Swimmers told to avoid Hutt River after discovery of 'potentially fatal' toxic algae

Quick Hutt River Facts

Injured tramper Brian Carey, a 14-year-old Naenae College pupil, rafted down the Hutt River gorge on a truck tyre tube in 1965. Tararua Tramping Club searchers rescued him after he slipped on ice near Alpha and fell over a bluff. (File photo)

56 kilometres long
Runs through the Hutt Valley from Kaitoke to Wellington Harbour
Catchment size: 655 square kilometres, nearly seven times Wellington Harbour
Four main tributaries: Akatarawa, Mangaroa, Pakuratahi and Whakatiki

Flowing south-west from its headwaters in the Kaitoke Regional Park, the Hutt River passes through a catchment that changes from rural land, to dense residential communities, to commercial and industrial facilities in Lower Hutt and Petone as it drains into Wellington Harbour.

The river and its floodplains hold cultural significance to iwi. A healthy river has healthy mauri, which enables healthy connections and relationships.

Spokesperson for Choose Clean Water Marnie Prickett said the Hutt River was a “multiple impact site”.

“People don’t see themselves as existing in a catchment,” she said, with residents unwittingly polluting the river in many little ways, like putting soapy water down stormwater drains.

The abundance of pavement removed the ground’s natural ability to absorb water, resulting in pooling, flooding, and sediment being carried along natural low points to the river.

Dr Jenny Webster-Brown, incoming director at Our Land and Water National Science Challenge and adjunct professor at Lincoln and Canterbury Universities, said Hutt River was a classic case of “urban stream syndrome”.

Flood control meant confining the river to one course, which meant contaminants were more concentrated, and the water level varied more dramatically during heavy rain, as it was unable to spread out.

Common contaminants like copper, lead, and zinc, and hydrocarbons like petrol, were toxic to river ecology, and fertilized parks, golf courses, and farmland caused elevated levels of nitrate and phosphorus.

Higher concentrations of sediment meant murky water, which affected predator/prey relationships. “You can’t see your food, and your food can’t see you to get away,” she said.

Toxic algae is poisonous if consumed, and the regional council often issues warnings to dog owners to keep an eye on pets when walking by the river.

Filter feeders ended up sucking in silt rather than clean water, and the sediment which settled on the river bottom obscured habitats and food.

In November last year, 66 little blue penguins born on Matiu/Somes Island died, it was thought, because of silt entering the harbour from the Hutt River obscuring their food.

River health

Hutt River at Te Marua Intake – in the upper reaches of the catchment – rated A: the predicted average infection risk is 1 in 100 people.

Wellington resident Paul Aschenberger took this photo of Evans Bay in Wellington Harbour, showing the effects of muddy runoff from the Hutt River, a common occurrence after heavy rain.

Opposite Manor Park Golf Club – between Upper and Lower Hutt city centres – rated D: the predicted average infection risk is more than 3 in 100 people.

Hutt River at Boulcott – between Kennedy-Good Bridge and Melling Bridge – rated D

Wellington Regional Council marine and freshwater team leader Dr Evan Harrison said risk was determined by combining information about recent and forecast weather, and previous results.

Suitability for swimming was monitored daily, year-round, along with toxic algae growth, which was harmful to humans and dogs, with alerts and ratings published on the Land, Air, Water Aotearoa (LAWA) website.

Chair of local volunteer group Friends of the Hutt River, Pat Van Berkel, said algae began appearing in the river just over a decade ago.

Block Rd in Lower Hutt shows the effects of a swollen Hutt River, which burst its banks after heavy rain. (File photo)

Van Berkel is also a member of Whaitua te Whanganui-a-Tara Committee, a group of locals from Hutt Valley and Wellington, co-managed by mana whenua, tasked by the regional council with developing a programme to improve the quality of streams, rivers and the harbour.

After two years of work, the committee was preparing to deliver its recommendations to the regional council.

Algae would only grow when nutrient levels – nitrogen and phosphate – occurred in concentrations between 5 and 10 per cent.

“You can’t eliminate it, it grows when the conditions are right.” A big part of the committee’s work was to figure out how to make conditions wrong.

“We know the amount of toxic algae in the winter time is less,” Van Berkel said. “After a storm, there is none.

Wilderlab founder Shaun Wilkinson takes eDNA samples from the water in the Hutt River to get an idea which species are present.

“There has been talk of releasing a lot of water all at once from a reservoir to flush it out,” he said, but that was deemed too destructive.

The solution would instead be to reduce nutrient levels to less than 5 per cent. Van Berkel said 22 per cent of nutrients in the Hutt River came from the Mangaroa River, 17 per cent from the Pakuratahi, 11 per cent from the Akatarawa, and 5 per cent from the Whakatiki.

Water is forced through a filter on the end of the syringe, which is then analysed back at the lab to identify DNA.

Springs in the river, between the Silverstream and Moonshine bridges, accounted for a further 40 per cent of nutrients.

“It’s not possible to plug up the springs,” Van Berkel said, so the question was; how did the nutrients, which emerged through the springs, first get into the groundwater?

Green algae, seen on the rocks behind Wilkinson, was present in high quantities in the eDNA samples.

Possible contributors, Van Berkel said, were fertilizer from parks and grounds, broken sewerage pipes, and septic tank failures. The recommendation to council would be to investigate these, and stop contaminants at their source.

The wastewater system was also frequently overwhelmed by periods of heavy rain, and flowed into the river. Plumbers saved time and money by discharging fresh water through the waste water pipes – “but that’s illegal for this very reason.”

Flooding

Regional council floodplain management team leader Sharyn Westlake said the existing stopbank system could handle at least a one-in-100 year flood, on a scale of 1944 cubic metres per second.

As part of the RiverLink project, the council would increase protection to handle floods of 2800 cubic metres per second.

“These stopbanks will protect Hutt City from estimated damages worth $1.1 billion,” she said. “And these estimates are only for direct costs of buildings and infrastructure, they don’t include human suffering that would occur within the community.”

Wildlife

The Hutt River catchment is home to 13 native fish species: longfin eel, shortfin eel, koaro, inanga, dwarf galaxias, giant kokopu, banded kokopu, Cran’s bully, bluegill bully, redfin bully, common bully, common smelt and lamprey.

More than half of these species are at risk or threatened.

Wilderlab founder Shaun Wilkinson sampled the river at two locations; Hikoikoi Reserve near the rivermouth, where it flowed into Wellington Harbour, and Railway Ave Bridge, in the heart of Lower Hutt city.

With three samples at each site, the detection rate should be between 85-90 per cent, Wilkinson said.

As well as some of the species on this list – long fin and short fin eels, inanga, common smelt, bluegill bullies, common bully – he found DNA from black flounder, which is native, but not common, at the bridge site.

Ulva, a kind of green, slimy algae, was the most common species at the river mouth, visibly choking the shallows. Also present in large numbers were estuarine triplefin, yelloweye mullet, and common or crans bullies (genetically indistinguishable).

An eel, which watched boldly on as Wilkinson took water samples, turned out to be a shortfin eel, a species abundant at both sites.

Upstream, the most common species were common/crans and blue bullies. Some surprising residents were the craspedacusta sowerbii, or peach blossom, freshwater jellyfish, an introduced species plaguing rivers and lakes around New Zealand.

“We’ve done a lot of rivers recently,” Wilkinson said. “Here we identified 210 species, and that’s pretty standard.”

Hutt River is an important trout fishery and spawning waters in the regional council’s Proposed Natural Resources Plan.

Suitable inanga spawning habitat was found in the Hutt River, and spawning has been confirmed in the lower reaches around the Sladden Park Boat Ramp.

An ongoing project for the regional council and community groups was planting locally indigenous species throughout the river corridor to improve water quality and stabilise river banks, enhance biodiversity, and provide shade and shelter for people and wildlife alike.