Restoring the river
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 second story in a series on Wellington’s waterways, Kate Green reports on the health of Waikanae River.
Waikanae River meanders through sloping ranges of mature forest, regenerating bush, gravelly banks and open pasture, down to the coastal sand dunes of the Ka¯ piti Coast.
Now, local iwi and local authorities have joined forces to create a group called Waikanae ki Uta ki Tai (‘‘mountains to sea’’) to improve the health of Waikanae River. Comprising Atiawa ki Whakarongotai, district and regional councils, and the Department of Conservation, they secured an $8.5 million four-year Jobs for Nature grant last year.
Local resident John Barrett (A¯ tiawa ki Whakarongotai) is just waiting for the day he can once again serve freshly caught eels from its depths on the marae.
Barrett is a member of the governance group for both the Waikanae Jobs for Nature programme and Waikanae ki Uta ki Tai. To mana whenua, a river is not just a body of running water, but has direct links to mana (spiritual health of the people) and manaakitanga (kindness).
Restoring the river’s health was a long-term project, Barrett said, and many governing bodies and community groups were involved.
‘‘There’s a hell of a lot of work going on, and a lot of planning,’’ he said. ‘‘What we are seeing is significant and tangible community input into the planning to make the money worthwhile.’’
Rigorous predator trapping was taking place in the Akatarawa ranges, at the headwaters of the river, and planting was ongoing along the banks and in the estuary.
Much of the riverbank falls into protected zones identified by the regional council as ‘‘Key Native Ecosystem’’ (KNE) sites along the river. They are some of the best examples of lowland riparian forest in the region with hugely diverse ecosystems.
Regional council biodiversity management team leader Richard Romijn said these were home to nine plant and five freshwater fish species listed as nationally threatened, and two plant and one bird species listed as regionally threatened.
Chair of Friends of Waikanae River Russell Bell pointed out it wouldn’t take much to see the whole length of the river’s course protected in this way.
The Friends of Waikanae River group grew native seedlings, giving them out to anyone who wanted to plant them on the riverbank in the area from Old Main Rd down to the estuary. ‘‘We already have trees growing for next year,’’ Bell said.
The catchment’s diverse landscape was an important connector between the mountains and the sea, Romijn said. ‘‘It creates an ecological corridor that links the Tararua Ranges, the Waikanae River estuary, the Ka¯ piti Marine Reserve and the Ka¯ piti Island Nature Reserve.’’
This formed ‘‘a network of habitat stepping stones’’ allowing forest birds to forage and breed throughout the area.
The biggest threats to the river’s ecology were weeds and pest animals, Romijn said, and Bell said the river was often choked by weeds, with banana passionfruit particularly fast-growing.
Drinking water supply
The river has been supplying Waikanae, Paraparaumu and Raumati with drinking water since 1977. It now serves about 38,600 people.
During periods of low flow, groundwater from the Waikanae borefield is used to recharge the river, meaning water can continue to be sourced from the river rather than putting bore water directly into the supply.
The Waikanae Borefield was last used for river recharge on March 6, 2021, and to top up the water supply on April 8, 2015.
But water from the bore contained more phosphates, so the long-term effect of this solution was unknown, Bell said.
Flooding
Regional council’s flood protection manager Graeme Campbell said the river was prone to flooding, so work had gone in to protect homes, trails and the integrity of the riverbank, including a recent upgrade of stop bank at Jim Cooke Park last year.
‘‘A major flood in the Waikanae River could cause millions of dollars’ worth of damage,’’ Campbell said.
A section of the popular Waikanae River Trail had already eroded away, and the council was working on an option to provide the river more room, while still allowing the roughly 80,000 annual visitors to keep using the trail.
Frequent floods in the spring and summer of 2017 caused hundreds of thousands of dollars in damage to river trails and flood defences, and in 2019 about 3000 cubic metres of gravel was scooped from the river, costing around $80,000.
River health
Marine and freshwater team leader Dr Evan Harrison said the lower reaches of the catchment bore the negative impacts of land runoff, sedimentation and human activity.
The regional council undertook monthly nutrient-level testing (for phosphate and nitrate) and yearly ecology testing (for macro invertebrates).
E. coli testing was done weekly in November and December, then fortnightly during January and March, at two points along the water.
The site at Mangaone Walkway was not rated; the Greenaway Rd site was rated A.
Swim safety was predicted each day by a model informed by the latest data, and published on the Land, Air, Water Aotearoa (LAWA) website.
As of June 10, sites at State Highway 1 and Jim Cooke Park were both marked as suitable for swimming.
Toxic algal blooms could occur in rivers and streams which were generally considered to have good water quality. Especially during summer, warmer temperatures and long dry periods caused cyanobacteria to form extensive blooms which were toxic, particularly to dogs.
But algae wasn’t the only thing growing and making its home in the river.
Wilderlab founder Shaun Wilkinson said a couple of things stood out from samples of eDNA taken from two river sites, at the end of Greenaway Rd and within the estuary.
The tests showed traces of dwarf galaxias, which were not known to live in the Waikanae. ‘‘It’s likely DNA was carried down from a population much further up in the ranges,’’ he said.
There was a ‘‘fair bit’’ of lamprey DNA present – ‘‘which is always a good thing’’, Wilkinson said – and traces of horses. ‘‘Meg [a Wilderlab colleague] mentioned there were lots of them milling around.’’
There were four species of flounder in the estuary samples. ‘‘It seems like the estuary could be an important nursery habitat for these species.’’
There was no trace of hornwort or other invasive macrophytes. ‘‘We picked up loads of hornwort from the O¯ taki, so it’s encouraging to see that it doesn’t seem to have made it to Waikanae – yet.’’
Out to sea
Waikanae Estuary Scenic Reserve chair Robin Gunston said the group had planted around 66,000 native seedlings in 17 years, around two-thirds of them raised in their on-site nursery.
The scientific reserve was set up by DOC in 1987 and fell into disarray, but in 2004 a group of locals set out to tidy it up. It was mostly sand dunes then, overrun by blackberry and gorse. The group has unearthed building materials and rubbish dumped there more than a decade before; they had once discovered the base of a bach in the dunes, and this week uncovered a massive tractor tyre.
Today the group was 165 members strong, and raised more than 3000 plants each year.
The estuary was a working scientific reserve, hosting studies which could hold huge implications for our future.
‘‘We get pretty upset when we find dogs off-lead, making deposits and digging up plants – it takes three years to raise a plant,’’ Gunston said. ‘‘We need greater public understanding. We’re trying to do this for the greater benefit of New Zealand as a whole.’’
Estuaries were ‘‘places of enormous change,’’ Gunston said. ‘‘Over a year the entrance of the river from the sea can move by 100 metres.’’
Recently they had noticed ‘‘the increasing power of the sea’’, with significant erosion already happening in the lower estuary, the result of climate change and extreme weather.
Intense rainfall washed fine sediment down the river into the estuary, with rocky sediment lodging mid-stream and forming islands which slowly became their own little ecosystems as the water stagnated and plants began to grow. Channels dug to straighten the river had the effect of concentrating the flow, making it faster. ‘‘Instead of things settling on bends in the river, they get carried downstream.’’
The final destination of the river was the sea. The plume from the outlet of the river was quite visible from aerial photos halfway out to Ka¯ piti Island, Gunston said.
This was an area of potential future study. What was sustainable here in terms of the nutrient levels? And what effect would changes in the river have on the inhabitants of the marine reserve? Only time would tell.