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Wairau River

Marlborough Online

14/12/2010

Rainbow valley
The upper reaches of the Wairau looking south with the
St. Arnaud Range to the right.
© Christopher Cookson

The Wairau River is Marlborough's largest river. It has a drainage area of 2600 square kilometres and is 257km long. Maori aptly named it "many waters" owing to it being largely a braided river. The Wairau's main tributaries are the Branch, the Waihopai and Rainbow rivers. The Wairau rises in the Spencer mountains and runs from the south to the north before turning to follow a part of the alpine fault line filled by glacial outwash. This leads more or less straight to the sea. A series of glacial moraine deposits west of Wairau Valley used to contain sizeable lakes before European times but signs of them can still be seen along the main road to Rotoiti.

Most of the Wairau Plain was forested before humans arrived but with the advent of fire large areas on the eastern side were cleared and failed to regenerate. At time Europeans arrived large areas swamp and swamp forest covered the lower plains and the Wairau wandered freely amongst it. The north bank of the Wairau was almost entirely forested in mixed podocarp broadleaf forest while the southern side was tall tussock grassland.

Wairau River

The Wairau River as seen from the north bank, clearly
illustrating the braided form typical of many NZ rivers
© Marlborough Online

The Wairau today, is a major source of water for the many crops grown on the plains and is famous for its fishing, particularly in the lower reaches, but it has also been responsible for threatening the very existence of many people in some of its floods which have reached over 55000cumecs.

The Wairau is fed by a number of tributaries including the Goulter River, the Branch River, The Waihopi River amongst others. The river enters the sea at the Wairau Bar, where it feeds an extensive area of lagoons which is an important wildlife habitat, and originally an important source of food for Maori.

Due to flooding problems, a second artificial outlet for the Wairau was created, the Wairau Diversion. This has become a popular fishing and picnic spot.

The lower reaches of the river are navigable, and in the early years of European settlement, vessels used the Wairau as part of an important connection between Blenheim and Wellington.

The last important merchant vessel, the Echo , retired in the 1960s.

With growing electricity needs in the region, an electricity generation company Trustpower, has proposed a series of canals to take water from the Wairau to feed generators. There has been a considerable amount of public opposition to the proposal due to concerns over the effect on the environment, including potential loss of recreational fisheries.