The character of a river is largely determined by the landscape through which it runs. Most New Zealand rivers flow through wild areas such as bush or hill country, and through farmland. Some also pass through towns and cities, such as the Avon in Christchurch and the Leith in Dunedin. Many rivers change in nature as they flow from the mountains to the sea.
Nine large areas of New Zealand, each with different landscape features, have produced distinct types of rivers.
Northland and Coromandel
These two peninsulas have many short rivers. The lower courses of some have become arms of the sea, as at Hokianga and Whitianga. The longest river in this region, the Northern Wairoa, feeds the large, estuarine Kaipara Harbour.
The major rivers in this region are alluvial: they flow through flood plains they have created by depositing sediment. The Waikato (New Zealand’s longest river), Waihou and Piako are the main examples.
Volcanic Plateau and Bay of Plenty
Recent volcanic activity has shaped the course and character of the rivers in these regions. Lakes that formed in volcanic craters are drained by the Tarawera, Kaituna and upper Waikato rivers. Part of the course of the Rangitāiki River is confined between the ranges of the main divide and the edge of the Volcanic Plateau.
The main range and east
Along the main range of the North Island and through the hill country to its east, rivers are incised and some are fast flowing. The major rivers are the Mōtū, Waiapu, Waipaoa, Wairoa, Mōhaka, Ngaruroro, Tukituki and Ruamāhanga. Some, notably the Waipaoa, Ngaruroro, Tukituki and Ruamāhanga, have formed flood plains.
While landscape generally determines the character of rivers, sometimes the reverse occurs. After it reaches Marton, the Rangitīkei River flows between sandstone banks that have an extraordinary sequence of terraces. These are the remnants of ancient flood plains that the river built and then cut down over a period of 250,000 years.
In the western uplands of the North Island (Taranaki, Rangitīkei and Manawatū), rivers incise deeply and often flow through long gorges. Examples are the Mōkau, Waitara, Pātea, Waitōtara, Whanganui, Whangaehu, Turakina and Rangitīkei rivers. To the south, the Manawatū River has formed a flood plain.
West of the main divide
Rivers west of the main divide, in north-west Nelson and Westland, have their headwaters in very mountainous areas and flow swiftly. The major river here is the wild Buller River, known for its white-water rapids and scenic gorges. Other examples are the Motueka, Grey, Taramakau and Arahura rivers.
Marlborough and Canterbury
Marlborough, Canterbury and South Canterbury are famous for their braided rivers, which rise in the Southern Alps and are glacial in origin. Once they reach the plains, the rivers break into many strands, interlaced across broad gravel beds made of glacial outwash. The Wairau, Awatere, Clarence, Waiau, Hurunui, Waimakariri, Rangitātā, Rakaia and Waitaki rivers are the main braided rivers. They are separated by shorter rivers arising in the foothills, notably the Ashley, Selwyn and Ashburton, which are not braided.
The Clutha is New Zealand’s largest river by volume. The greatest recorded flow was in 1878, when it surged at an estimated 5,663 cubic metres per second.
Otago’s rivers also have their origins in the Southern Alps, but they flow through basins in schist blocks. The Clutha, the Taieri and the Shag (Waihemo) are the main examples.
The rivers in Southland are alluvial, like those in the Waikato region. The main ones are the Mataura, Ōreti, Aparima and Waiau rivers.