The Motueka River drains one of the wettest, steepest catchments at the top of the South Island and ends its journey on a flat gravel plain where most of the district’s people live. That combination has made the lower valley one of New Zealand’s more reliably flood prone places, a fact written into more than 150 years of records and confirmed again in the winter of 2025. The map above shows the modelled flood depth for the lower river, the township, Riwaka and Brooklyn if the Motueka overtops or breaches its stopbanks in a major flood, drawn from Tasman District Council’s own flood model.
Switch between a one in 100 year flood and a one in 50 year flood, turn on the recorded extents of past floods, and tap any town to see who sits in the water’s path. What follows is the story behind the map.
The river and its catchment
The Motueka rises in the Red Hills in the south east of the catchment and runs about 116 kilometres north to Tasman Bay, where it enters the sea beside Motueka township. Its catchment covers a little over 2,000 square kilometres and gathers water from a string of tributaries, among them the Motupiko, the Wangapeka, the Baton, the Pearse and the Tadmor. By the time it reaches the coast the river is delivering the large majority of the fresh water that flows into Tasman Bay.
For most of its length the Motueka is a gravel bed river. It carries a heavy load of shingle down from the hills and drops it on the lower gradient near the coast, building up its own bed over time. That process, known as aggradation, slowly lifts the river relative to the land beside it and is one of the reasons the lower valley floods.
Why the lower valley floods
Three things line up against the lower Motueka. The catchment is steep and high, so heavy rain runs off quickly and arrives in a hurry. The rainfall itself can be extreme, with the ranges behind Nelson and Tasman among the wettest country in the North of the South Island. And the river’s gravel bed reduces the channel’s capacity to carry that water away, so when a large flood comes the river spreads sideways across the plain it has built.
The shape of the land does the rest. Motueka township, the Riwaka Plains and the Brooklyn area sit on low, flat, fertile ground that is only there because the river has flooded across it for thousands of years. The same soils that make the district one of the country’s best horticultural areas are a flood deposit, and the river has not finished making them.
The lower Motueka floodplain is not empty country. It carries the bulk of the district’s population, spread through a string of towns and valley settlements that each face the river in a different way. Here is who sits in the flood zones, from the coast inland.
Motueka township flood risk
Motueka is the largest settlement on the floodplain, with a population of 8,190 at the 2023 census, and the most exposed. It is built on the river delta and shielded by stopbanks along the lower Motueka River. Tasman District Council’s flood modelling finds that parts of the town would flood if those banks were overtopped or breached in a large flood, which is the scenario the map above shows. The low ground toward Peach Island and the streets nearest the river are where the modelled water sits deepest.
Riwaka and the Riwaka Plains
North of the township, the flat Riwaka Plains around the Riuwaka River hold the village of Riwaka, home to 756 people. The plains flood from the Riuwaka rather than the main Motueka, and the combination of a low coast and a quick mountain river makes them one of the first places to go under. Evacuation orders were issued at Riwaka in the 2018 cyclones and again in the floods of 2025.
Brooklyn and Brooklyn Stream
Brooklyn sits where Brooklyn Stream meets the Motueka, and the stream is one of the three watercourses singled out in the council’s 2020 flood mitigation study for the area. Riverside homes at Brooklyn were among those evacuated when the Motueka rose in July 2025. It is a small rural settlement, but its position at a confluence puts it squarely in the path of a large flood.
Lower Moutere
Lower Moutere, a village of 513 people, sits on the southern edge of the floodplain between the Moutere and Motueka catchments. It is more sheltered than the riverside settlements, but the surrounding low country drains slowly, and heavy rain ponds across the flats around the village.
Ngātīmoti
Ngātīmoti, with 321 residents, lies in the middle valley directly on the Motueka River and largely without stopbanks. In June 2025 the Civil Defence controller described the flood here as the biggest since 1877, and up to a metre higher than the major flood of 1983. For a settlement that depends on the river staying in its channel, that is as stark a warning as the record holds.
Woodstock and the upper Motueka Valley
Woodstock sits on the valley road beside the river and gives its name to the council’s long-running Woodstock flow gauge, the instrument that measures how high the Motueka is running. Further up the valley are Tapawera, Tadmor and Kohatu, small rural and orchard communities on open floodplain. A private stopbank near the Tapawera bridge burst in the 2025 flood, spilling rock and debris across farmland. These upper settlements rely entirely on the river behaving, and when it does not they are the first to be cut off.
Flood protection since 1982
The serious floods of January 1895, July 1929, June 1954 and April 1957 prompted a long programme of river works that became the Motueka Catchment Control Scheme, completed in 1982. The lower Motueka stopbanks themselves date from the late 1950s and were built to a one in 50 year standard, originally to protect farmland rather than houses. Decades on, the township has grown up behind them.
That history matters because the banks were never designed to hold back the largest floods. Tasman District Council’s flood hazard work, including the Motueka, Brooklyn and Riuwaka Flood Mitigation Study of July 2020, identifies points where the stopbanks are expected to overtop in both a one in 50 and a one in 100 year flood, and warns that parts of Motueka are exposed to flooding if the banks are breached. The council has since begun a Lower Motueka floodbank improvement project to lift that level of protection. The map’s flood zones are not a prediction that the town will flood tomorrow. They are a picture of what the modelling says happens when a flood large enough to beat the banks arrives.
A history of flooding
The benchmark event is the great flood of February 1877, remembered locally as the Old Man Flood, which changed the course of the river in places and was still the measuring stick nearly 150 years later. Major floods followed through the twentieth century, and the river kept testing the valley into the modern era. In May 2010 around 20 homes were flooded near Tapawera in the Wangapeka area and residents were evacuated. In February 2018 the back to back ex tropical cyclones Fehi and Gita brought a Nelson Tasman state of emergency and significant flooding on the Riwaka Plains. Heavy rain returned in 2021, and in August 2022 an atmospheric river dumped what was assessed as close to a one in 100 year rainfall on the region, triggering hundreds of landslides and affecting around 600 properties across Nelson and Tasman.
The June 2025 floods
The winter of 2025 brought the worst of it for a generation. Three pulses of rain in late June and early July, beginning on 26 June, dropped more than 300 millimetres across parts of Tasman, with Nelson recording its wettest June on record. A state of emergency was declared for Nelson and Tasman on 27 June and later extended as the second and third downpours arrived.
The Motueka Valley was the hardest hit area. Evacuation orders went out for Tapawera, Tadmor and Riwaka, riverside homes at Brooklyn were cleared, and by 11 July Civil Defence had evacuated around 100 homes. Seventeen homes were uninhabitable by the end of June, and about 650 properties were eventually assessed. At Ngātīmoti the Civil Defence controller described it as the biggest flood since 1877, up to a metre higher than the major flood of 1983. A private stopbank near the Tapawera bridge burst, spilling rock and woody debris across farmland. One Motueka Valley tiny home was gutted and carried some 400 metres down the river. A kiwifruit orchard went under to the top of its vines. A Tasman man working on the recovery was killed by a falling tree as he cleared flood damage.
For the people in the valley the losses were total and personal. “People have lost their homes around here, we know quite a few people who have lost everything,” Julie, the partner of valley resident Steve Segee, told RNZ as the water receded.
Climate change and flood risk
It is tempting to file every big flood under climate change, but the scientists who study these events are careful, and so should anyone reporting them. Asked whether warming had changed how often a flood like June 2025 happens, Dr Daithi Stone of Earth Sciences New Zealand said plainly that “we don’t know at the moment.” What is well established is the physics, that warmer air holds more moisture, and the warming already observed equates to roughly 10 percent more water available to fall as rain. The 2025 event was driven in large part by an unusual northerly feed of moisture and a storm that stalled over the region, the kind of weather pattern that has always produced the valley’s worst floods.
Where the science is clearer is the trend ahead. Climate projections, as Earth Sciences New Zealand’s Dr Emily Lane notes, show extreme rainfall becoming more frequent and more severe, and Tasman District Council’s own climate work expects heavier winter and spring rainfall through the century. The honest summary is that the lower Motueka is flood prone for reasons of geography and gravel that have nothing to do with climate change, and that a warming climate is loading the dice toward the heavy rainfall that sets those floods off.
What happens next
The 2025 floods reopened a long running argument about the river’s gravel. Some upper valley farmers say shingle has been allowed to build up in the bed, raising the river and cutting its capacity to carry floods, and point to council figures showing hundreds of thousands of cubic metres accumulated in the upper Motueka since the late 1980s. The council counters that recent survey data shows the bed has lost gravel in places in the past few years, and warns that stripping shingle out at scale can deepen and destabilise the channel rather than tame it. Both can be partly true on a river this large, and the debate over how to manage it is likely to outlast the current recovery.
What is not in dispute is the exposure. The valley grows apples, hops and kiwifruit on the very ground the river floods, the township has expanded behind banks built for a smaller task, and the population swells each year with seasonal workers during the harvest. The map at the top of this page is a standing reminder of where the water goes when the river wins. The towns of the lower Motueka have lived with that risk for a century and a half, and they will go on living with it.
Sources for this story include Tasman District Council’s flooding and natural hazards pages and flood model, the Science Media Centre expert reaction of 1 July 2025, and RNZ’s reporting from the Motueka Valley during the 2025 floods. Census figures are from Stats New Zealand. The flood map is built directly from Tasman District Council’s published flood depth model and recorded flood extents.
Have you been flooded in the Motueka Valley, or do you live behind the stopbanks in town? Share what you have seen the river do in the comments below.
This article was written by AI, briefed to report the facts, hopefully without some of the bias people bring to the job 🙂
Leave a Reply