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The Clutha River (, officially gazetted as Clutha River / italic=no) is the second longest river in New Zealand and the longest in the South Island. It flows south-southeast through Central Otago and South Otago from Lake Wānaka in the Southern Alps to the Pacific Ocean, south west of Dunedin. Gold is in abundance in the Clutha River and its surrounding areas. It is the highest volume river in New Zealand, and has a discharging mean flow of . NIWA's use of Hydro2de
The Clutha River played a prominent role in both the Māori and European history of the area. Rivers and valleys were the main transport system used by local Māori to access the interior of the South Island. The 1860s Otago gold rush resulted in the production of approximately 240 tonnes of gold, which was found in the Clutha catchment. It has the biggest catchment and outflow in New Zealand. About 6% of all water in the South Island is discharged by the Clutha River alone. It has a mean discharge of approximately and a catchment area of around and is an economically significant river for the country. The Clutha River encompasses two hydropower stations, which provide 14% of the country's hydropower generation capacity.
The Clutha River drains the high mountains of the Southern Alps in the west and passes through a complex topographic system of basins and ranges towards the east before reaching into the Pacific Ocean. A majority of the topographical features of the Clutha River catchment area are a direct result of the late Cenozoic and active tectonic processes that are occurring in southern South Island due to deformation along the nearby plate boundary, defined by the Alpine Fault.
The river is known for its scenery, gold-rush history, and swift turquoise waters. A river conservation group, the Clutha Mata-Au River Parkway Group, is working to establish a regional river parkway, with a trail, along the entire river corridor.
The first appearance of a European name for the Clutha River / Mata-Au was the Molyneux River (); its mouth was named by Captain James Cook after his sailing master, Robert Molineux. The name is also applied to the small settlement of Port Molyneux. Early maps show Moulineux Harbour in its original spelling, but later maps indicate the harbour's name was written as "Molyneux", rather than "Moulineux".
The river is now commonly known as the Clutha, which comes from Cluaidh, the Scots Gaelic name for the River Clyde in Scotland, which runs through Glasgow. Otago Witness, 20.3.1923
The official name for the river has been Clutha River / Mata-au since the Ngāi Tahu Claims Settlement Act 1998, a landmark Treaty of Waitangi settlement, which added dual names to approximately 90 geographic features throughout the South Island to recognise the "equal and special significance" of both the English and Māori names.
The mouth of Mata-au was heavily populated, with many permanent and temporary Kāi Tahu settlements throughout the lower stretches of the river. Murikauhaka, a settlement near the mouth of the Mata-au, was at one stage home to an estimated two hundred people. Māori trading groups used the Cromwell Gorge as the main thoroughfare to their pounamu and moa-hunting expeditions to the interior of Otago.
Many early Māori archaeological sites have been found in the Cromwell Gorge, featuring moa eggshell fragments. Unlike other Central Otago sites, no burned bones have been found.
The first European to visit the Upper Clutha area and to see the inland lakes of Lake Wakatipu, Wānaka and Hāwea was Nathanael Chalmers, who was guided by Chiefs Reko and Kaikōura in 1853. They returned him down the river on a mōkihi, a flax reed open kayak, that they built from flax stems and raupō from the shores of Lake Hāwea. In 1910, 57 years after the event, Nathanael Chalmers remembered his boat trip through the Cromwell Gorge: "I shall never forget the "race" through the gorge ... my heart was literally in my mouth, but those two old men seemed to care nothing for the current."
European "sheepmen" arrived later in the late 1850s, searching for grazing grounds in Otago's interior. Alexander and Watson Shennan set off from Milton (known previously as Tokomairiro) in December 1857 to Central Otago, looking for land to raise sheep. The brothers proceeded farther than the runholders who had previously acquired territory up to the Waitāhuna River. When they returned to Dunedin after spending several days exploring the Manuherikia Valley, they submitted an application to the Otago Provincial Government to lease two blocks of land on either side of the Manuherikia River. The total land area was . They brought sheep to the district in 1858. Watson Shennan described the area as "well grassed and watered, a very land of promise" which attracted others to the region.
In 1862, gold-rich bars of rocks and gravel were discovered by Christopher Reilly and Horatio Hartley during their winter 1862 expedition up Cromwell Gorge through the waters of the Clutha. They arrived in Dunedin on 15 August, 1862, deposited their of gold, and were rewarded with £2,000.
Around 100 have operated at various times during the area's history in the river bed and nearby gravels, including the present-day gorge to the east of the Old Man Range. The Clutha River and its tributary Kawarau transported alluvial gold across a distance of in river bed load. A Middle Pleistocene-age ancestral Clutha River delivered detrital gold across the lower parts of what is presently the Manuherikia Valley near Alexandra.
By Christmas 1861, 14,000 prospectors were on the Tuapeka and Waipori fields. The gold rush was short-lived, with most of the alluvial gold played out by 1863, but prospectors continued to arrive, swelling to a maximum of 18,000 miners in February 1864.McKinnon, M. (ed.), Bradley, B. & Kirkpatrick, R. (1997). New Zealand Historical Atlas: Ko Papatuanuku e Takoto Nei. Auckland: David Bateman Ltd. .
Mining in the Clutha River upstream from Cromwell became significant after 1900, when the area's potential was gradually recognised. Previously, the Kawarau River and the Clutha River running downstream from Cromwell were the primary focus. Māori were aware of gold in the Clutha River but they did not value it.
In inland basins, annual precipitation totals can be less than , while on the western edge of the catchment, they can surpass . The contribution of snowmelt to the annual streamflow of the Clutha River is estimated to be 10% by the time it reaches the Southern Pacific Ocean. This proportion is considerably higher for alpine sub-catchments and large inland basins, rising as high as 30% to 50%. A number of large tributaries originate in Central Otago's semi-arid basins, where yearly precipitation can be as low as , which is an order of magnitude lower than on the Main Divide.
The mean flow of the Clutha is around , comparable to many much larger rivers. This heavy flow, combined with the relatively small size of the river in global terms, makes the Clutha notoriously fast-flowing. It is often listed as one of the world's most swiftly flowing rivers, alongside Australia's Macleay River and Fitzroy Rivers, the Amazon River and in South America, and the Teesta River in the Himalayas. The highest recorded flow on the Clutha was during heavy storms in 1978, peaking at .
At the minimum, nine species of freshwater-limited Galaxias have been identified in the Clutha River by genetics and morphology. These include range-limited species Endemism to particular tributaries such as the Nevis River and Teviot River subcatchments, and an alpine galaxias taxon unique to the upper Manuherikia catchment. A Nationally Critical species of Galaxias called "Clutha flathead species D" occurs in various parts of the catchment. A 2022 University of Otago genetic study published in the journal Diversity and Distributions revealed that the river is home to a diverse range of Galaxias vulgaris clades; its diversity is likely a reflection of the Clutha River's complex geological processes. The study emphasises the importance of the genome-wide methods to identify species and understand biodiversity in freshwater ecosystems and conservation in the Clutha River.
Before the construction of Roxburgh Dam, salmon could be found traversing the length of the Clutha River and spawning as far upstream as Lakes Hāwea and Wānaka. The Clutha is the southernmost recognised salmon river; salmon continue to arrive each spring and summer, though numbers have decreased since the construction of Roxburgh Dam. Common bully, smelt, and perch are also found in the river.
A 1981 assessment of the river by the Upper Clutha Valley Development with the Ministry of Works and Development emphasised the high-quality waters of the river and very low levels of phytoplankton biomasses present.
The 1978 flood breached the banks of rivers from the Ōreti in the south to the Tokomairaro. Over of land was inundated, with the loss of over 21,000 livestock. Towns and areas affected stretched from Makarora in the north to Invercargill in the south. The town of Wyndham was completely evacuated, and the towns of Balclutha, Milton and Mataura were seriously affected with many residents moved. The small settlement of Kelso on the banks of the Pomahaka River was completely abandoned and was not rebuilt once the waters subsided.Lloyd, K. (1978) Flood disaster 1978. Dunedin. At its peak, on 15 October, the Clutha's flow was measured at just over .Lind, C.A. (1978) The 100 year flood – 1978. Invercargill: Craig Printing Co.
A major flood in November 1999 seriously damaged river communities, especially Alexandra. The flooding in Alexandra was attributed to a rise in the riverbed resulting from silt loading in the Roxburgh reservoir behind the Roxburgh Dam, downriver from the town. The 1999 flood had significantly higher water levels in Alexandra than the 1878 flood, despite being only 80% of the volume of the latter.
The Clutha River's first dam was the Nil Desperandum Dam in the Upper Clutha Valley, existing from 1864–66. The Roxburgh Dam was the first substantial dam in the South Island. Construction on the dam began in 1949. Four were installed in 1956–57 and four more in 1960–61. Its installed capacity is 320MW.
Construction began on the Clyde Dam in 1982 and was completed in 1993. It was a somewhat controversial project, with opposition and criticism from environmentalists and local residents. Completion of the Clyde Dam took much longer than expected, at a final cost more than 45% higher than the first estimate. The Clyde Dam was one of Robert Muldoon's and the Third National Government's "Think Big" projects, an interventionist state economic strategy. Several Local Authorities along the Clutha River use it as a source for treatment plants to provide communities with potable water.
Further dam projects have been proposed for the river, but as of 2012, all have been cancelled.
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