Time is running out to protect Franz Josef from its rising river. Stopbanks won’t work forever
The Waiho River is rising faster because it deposits gravel along a confined bed. There is a strong case for letting the river roam naturally.
As the small South Island town of Franz Josef attracts over a million visitors each year, it sits at the crossroads of a rapidly changing Waiho River. The river, one of New Zealand's most dynamic, carries vast amounts of gravel from the Southern Alps, but is artificially confined to a smaller portion of its natural bed by stopbanks.
These man-made levees have prevented the river's gravel from spreading naturally, causing the riverbed to rise by about 20 centimeters per year - three times faster than it would without the stopbanks. This rising riverbed threatens the safety of the town, as the safety margin provided by the stopbanks shrinks as the riverbed grows.
In 2023, the independent Waiho Technical Advisory Group warned of the increasing threat posed by the rapidly rising riverbed. They proposed a ten-year plan focused on providing the river with more space to move its gravel, rather than relying on higher and higher stopbanks. However, by August 2025, the group's progress review found that the river was changing faster than the plan was being implemented, putting the town's safety at greater risk.
The Waiho River has been altering its course since 2010, increasingly spilling into the neighbouring, lower Tatare Stream. In the past year, this spill has carved out a new channel capturing more of the river's flow. The river's new path has cut down by two meters, surpassing modelled predictions. This erosion has already undermined the base of Havill’s Wall, which protects the town’s wastewater treatment ponds.
Despite these changes, the spillover into the Tatare Stream is also filling with sediment. When this channel is full, possibly within a decade, the Waiho is expected to return to its southern bed. As the new river channel cuts deeper, it exposes rock that protects the base of Havill’s Wall. Furthermore, an earthquake along the Alpine fault could compound the problem by damaging stopbanks and triggering landslides that deliver more gravel into the river, accelerating the riverbed rise.
Written by urgent.news from The Conversation AU's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
