Wanganui River

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title: "Wanganui River" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["westland-district", "rivers-of-the-west-coast-region", "rivers-of-new-zealand"] description: "River in New Zealand" topic_path: "geography/new-zealand" source: "https://en.wikipedia.org/wiki/Wanganui_River" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary River in New Zealand ::

::data[format=table title="Infobox river"]

Field	Value
name	Wanganui River
image	Wanganui River 03.jpg
subdivision_type1	Country
subdivision_name1	New Zealand
subdivision_type2	Region
subdivision_name2	West Coast
subdivision_type3	District
subdivision_name3	Westland
source1_location	Southern Alps
mouth_location	Tasman Sea
length	55 km
tributaries_left	Lambert River, Adams River, Oneone River
tributaries_right	Smyth River
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::callout[type=note]

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| name = Wanganui River | native_name = | image = Wanganui River 03.jpg | image_size = | image_caption = | subdivision_type1 = Country | subdivision_name1 = New Zealand | subdivision_type2 = Region | subdivision_name2 = West Coast | subdivision_type3 = District | subdivision_name3 = Westland | source1_location = Southern Alps | mouth_location = Tasman Sea | length = 55 km | source1_elevation = | mouth_elevation = | discharge1_avg = | basin_size = | tributaries_left = Lambert River, Adams River, Oneone River | tributaries_right = Smyth River

The Wanganui River is in the West Coast of the South Island of New Zealand. It flows northwest for 55 km from its headwaters in the Southern Alps, entering the Tasman Sea near Lake Ianthe, 40 km southwest of Hokitika.

After heavy rain in January 2013 the flooded river partially washed away the single-lane road bridge that carries , closing the only through road on the West Coast.

Gravel buildup has gradually raised the riverbed, and in 2021 the West Coast Regional Council planned to elevate stopbanks by 1 m at a cost of $5.7 million to protect neighbouring farmland from flooding. Farmers protested the rates rise that would be needed to pay back this 30-year loan, and suggested the Department of Conservation should contribute.

In March 2023, the river broke through a hole in the stopbank on the north side, and caused significant flooding damage to several farms.

In April 2023, a river engineer briefed local farmers, and outlined the history of development of stop banks on the river. In 1948, the river had a wide and natural braided river course. However, over a period of 60 years, stop banks were constructed along the original river bed to create pasture land. The result was that the river became increasing constrained, taking up only half of the area it previously occupied. The consequence is that the rate of aggradation has doubled. In the area 7 km downstream of the State Highway 6 bridge, the river now sits above the flood plain. The location where the river broke through the stop banks earlier in 2023 was the normal river bed in the 1960s. Construction of stop banks to narrow the river channel has also increased the gradient of the river bed, and increased the velocity of water flowing against the stop banks. Climate variability is producing more intense storms, and combined with the other factors, is increasing the threat of future breaches.

References

References

1. (3 January 2013). "Highway closed after bridge washout". [[The Press]].
2. Williams, Lois. (20 September 2021). "Farmer calls out Doc over cost of flood protection". Hokitika Guardian.
3. McMahon, Brendon. (9 March 2023). "Wanganui River in-flood flows onto farms after council 'failed' to heed warning".
4. McMahon, Brendon. (2023-04-22). "Stop banks 'strangle' West Coast river over 60 years".

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::