Wanganui River

Wanganui River
Wanganui River
Location
Country	New Zealand
Region	West Coast
District	Westland
Physical characteristics
Source
• location	Southern Alps
Mouth
• location	Tasman Sea
Length	55 kilometres (34 mi)
Basin features
Tributaries
• left	Lambert River, Adams River, Oneone River
• right	Smyth River

The Wanganui River is in the West Coast of the South Island of New Zealand. It flows northwest for 55 kilometres (34 mi) from its headwaters in the Southern Alps, entering the Tasman Sea near Lake Ianthe, 40 kilometres (25 mi) southwest of Hokitika.

After heavy rain in January 2013 the flooded river partially washed away the single-lane road bridge that carries State Highway 6, closing the only through road on the West Coast.^[1]

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.^[2]

In March 2023, the river broke through a hole in the stopbank on the north side, and caused significant flooding damage to several farms.^[3]

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 kilometres (4.3 mi) 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.^[4]

References

^ "Highway closed after bridge washout". The Press. 3 January 2013. Retrieved 3 January 2013.
^ Williams, Lois (20 September 2021). "Farmer calls out Doc over cost of flood protection". Hokitika Guardian. p. 3.
^ McMahon, Brendon (9 March 2023). "Wanganui River in-flood flows onto farms after council 'failed' to heed warning". RNZ. Retrieved 23 April 2023.
^ McMahon, Brendon (22 April 2023). "Stop banks 'strangle' West Coast river over 60 years". RNZ. Retrieved 23 April 2023.

43°02′07″S 170°25′50″E / 43.0353°S 170.4305°E / -43.0353; 170.4305

[1] "Highway closed after bridge washout". The Press. 3 January 2013. Retrieved 3 January 2013.

[2] Williams, Lois (20 September 2021). "Farmer calls out Doc over cost of flood protection". Hokitika Guardian. p. 3.

[3] McMahon, Brendon (9 March 2023). "Wanganui River in-flood flows onto farms after council 'failed' to heed warning". RNZ. Retrieved 23 April 2023.

[4] McMahon, Brendon (22 April 2023). "Stop banks 'strangle' West Coast river over 60 years". RNZ. Retrieved 23 April 2023.

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[2]

[3]

[4]

v t e Landforms of Westland District, New Zealand
Alpine passes	Arthur's Pass Browning Pass / Nōti Raureka Copland Pass Haast Pass
Bays	Bruce Bay Jackson Bay
Canyons, gorges and waterfalls	Fantail Falls Gates of Haast Hokitika Gorge Otira Gorge Roaring Billy Falls Thunder Creek Falls
Glaciers	Agassiz Glacier Douglas Glacier Fox Glacier Franz Josef Glacier Garden of Eden Ice Plateau Olivine Ice Plateau Volta Glacier
Headlands	Abut Head Awarua Point Gillespies Point Knights Point
Islands	Open Bay Islands
Lakes and lagoons	Abel Lake Alpine Lake / Ata Puai Lake Ellery Lake Gault Lake Ianthe Lake Kaniere Lake Mahinapua Lake Mapourika Lake Matheson Lake Moeraki Ōkārito Lagoon Lake Paringa Saltwater Lagoon Lake Wahapo
Mountain ranges	Butler Range Southern Alps
Mountains	Mount Adams Aoraki / Mount Cook Mount Aspiring / Tititea Mount Brewster Mount Dampier Mount Graham Mount Haast Mount Hopkins La Perouse Lendenfeld Peak Mount Rolleston Mount Sefton Silberhorn Mount Tasman Mount Vancouver Mount Whitcombe
River flats	Pleasant Flat
Rivers	Adams River Arahura River Arawhata River Balfour River Barlow River Barn River Bettne River Big Wainihinihi River Burke River Butler River Callery River Cascade River Clarke River Clearwater River Cook River / Weheka Copland River Cropp River Deception River Donald River Douglas River Drake River Duncan River Edison River Fork River Fox River Gorge River Gunn River Haast River Hacket River Hall River Hapuka River Harman River Hinatua River Hokitika River Hope River Jackson River Jerry River Kaniere River Karangarua River Kokatahi River Lambert River Landsborough River Lord River Macfarlane River Mahitahi River Jacobs River Manakaiaua River Maori River Martyr River Mikonui River Moeraki River Morse River Mueller River Mungo River Ngatau River North Barlow River Ohinemaka River Ōhinetamatea River Ōkārito River Okuru River Ōmoeroa River Oneone River Otehake River Ōtira River Ōtoko River Paringa River Perth River Poerua River Rolleston River Rotokino River Ruera River Ship Creek Smoothwater River Smyth River Spoon River Stafford River Strauchon River Styx River Taipo River Taramakau River Te Naihi River Te Rahotaiepa River Toaroha River Tōtara River Totarakaitorea River Troyte River Tuke River Turnbull River Waiatoto River Waiho River Waikūkūpa River Waipara River Waita River Waitaha River Waitangitāhuna River Waitangiroto River Wanganui River Whakaikai River Whakapohai River Whataroa River Whitcombe River Wilkinson River Willberg River Williamson River Wills River

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