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35-631: The Waitaki River is a large braided river in the South Island of New Zealand . It drains the Mackenzie Basin and runs 209 kilometres (130 mi) south-east to enter the Pacific Ocean between Timaru and Oamaru on the east coast. It starts at the confluence of the Ōhau and Tekapo rivers, now at the head of the artificial Lake Benmore , these rivers being fed by three large glacial lakes, Pukaki , Tekapo , and Ōhau at

70-406: A meandering river , which has a single sinuous channel. It is also distinct from an anastomosing river , which consist of multiple interweaving semi-permanent channels which are separated by floodplain rather than channel bars; these channels may themselves be braided. The physical processes that determine whether a river will be braided or meandering are not fully understood. However, there

105-542: A meandering profile. A stream with cohesive banks that are resistant to erosion will form narrow, deep, meandering channels, whereas a stream with highly erodible banks will form wide, shallow channels, preventing the helical flow of the water necessary for meandering and resulting in the formation of braided channels. Braided rivers occur in many environments, but are most common in wide valleys associated with mountainous regions or their piedmonts or in areas of coarse-grained sediments and limited growth of vegetation near

140-540: A 1.6 km (1 mi) tunnel to a power station below the level of the lake. The original Waitaki power stations discharge water back into the Waitaki River which then forms a storage lake for the next station in the chain. The three power stations are (commissioned/capacity/annual output): In the 1960s, work was started on the Upper Waitaki project. This project consisted of taking the discharge from

175-404: A dendritic system, or of cohesive sediments with no bedload transport. Meanders fully develop only when the river banks are sufficiently stabilized to limit lateral flow. An increase in suspended sediment relative to bedload allows the deposition of fine erosion -resistant material on the inside of a curve, which accentuated the curve and in some instances, causes a river to shift from a braided to

210-418: A failure of the Ōhau canal, Lake Ōhau can overflow a weir into the normally dry bed of the upper reaches of the Ōhau River and thus into Lake Ruataniwha. Also, if water cannot pass down the canal to Ōhau B then the excess inflows into the lake can be diverted by the spillway down the bed of the lower reaches of the Ōhau River to Lake Benmore . While limited the storage capacity of the lake also ensures that

245-687: A major contributing factor. A more modest successor scheme, the North Bank tunnel looked likely to proceed, with water rights being granted in 2009, but land access negotiations were suspended in January 2013 due to flat demand for electricity forecast for the next five years. Braided river Braided streams tend to occur in rivers with high sediment loads or coarse grain sizes, and in rivers with steeper slopes than typical rivers with straight or meandering channel patterns. They are also associated with rivers with rapid and frequent variation in

280-507: A proposal for a new series of canals and dams was made by Meridian Energy for irrigation and electricity generation on the river. This scheme, known as Project Aqua , planned to divert up to 77 percent of the lower river's flow to create a hydroelectric scheme, but these plans were dropped in March 2004. Lack of commercial viability was given as the major reason for the scheme's shelving, although strenuous public protest may also have been

315-426: A straight channel. Also important to channel development is the proportion of suspended load sediment to bed load . An increase in suspended sediment allowed for the deposition of fine erosion -resistant material on the inside of a curve, which accentuated the curve and in some instances, caused a river to shift from a braided to a meandering profile. These experimental results were expressed in formulas relating

350-402: A variation in sediment load, provided the amount of water carried by the river is unchanged. A threshold slope was experimentally determined to be 0.016 (ft/ft) for a 0.15 cu ft/s (0.0042 m /s) stream with poorly sorted coarse sand. Any slope over this threshold created a braided stream, while any slope under the threshold created a meandering stream or – for very low slopes –

385-641: Is 356 cubic metres per second (12,600 cu ft/s). The first major infrastructure improvements to the river were made between 1881 and 1914 with the construction of road and rail bridges at Kurow and Waitaki Bridge . The middle of the river bed formed a traditional political boundary between Canterbury and Otago . The term "south of the Waitaki" is often used to refer to the Otago and Southland regions as one common area (the two regions share historical and ethnic relationships which make them distinct from

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420-429: Is Kellands Pond, whose 22 hectare area occupies further gravel pits. There is a spillway (Gate 22) built into the dam which contains 3 gates with a total discharge capacity of 4,900 cubic metres per second which flows into the normally dry bed of the Ōhau River. The lake functions as a surge reservoir for the power scheme. If, during excessive inflows into Lake Ōhau which Ōhau A is unable to pass or, when there has been

455-461: Is fed by the output from the Ōhau A power station and also by an overflow discharge from Lake Ōhau down the normally dry bed of the Ōhau River. Ruataniwha discharges through a natural gap in the dam into a canal which feeds the Ōhau B power station. Immediately downstream is a connection to Wairepo Arm, a small lake. Connected to the Wairepo Arm by way of a culvert under State Highway 8

490-403: Is wide agreement that a river becomes braided when it carries an abundant supply of sediments. Experiments with flumes suggest that a river becomes braided when a threshold level of sediment load or slope is reached. On timescales long enough for the river to evolve, a sustained increase in sediment load will increase the bed slope of the river, so that a variation of slope is equivalent to

525-583: The Rakaia and Waitaki Rivers of New Zealand are not aggrading, due to retreating shorelines, but are nonetheless braided rivers. Variable discharge has also been identified as important in braided rivers, but this may be primarily due to the tendency for frequent floods to reduce bank vegetation and destabilize the banks, rather than because variable discharge is an essential part of braided river formation. Numerical models suggest that bedload transport (movement of sediment particles by rolling or bouncing along

560-691: The Waitaki hydroelectric project. It lies on the traditional boundary of the Canterbury and Otago provinces, with the town of Twizel two kilometres to the north. The lake takes its name from the Ruataniwha Station, a large sheep-station in the area, part of which the NZ Electricity Department purchased as the site for the township of Twizel (founded in 1968). Ruataniwha was a Māori chief who drowned when

595-540: The South Island Rowing Association made him its first life member. The lake's facilities can accommodate 600 rowing boats and 2000 competitors. The rowing course has eight lanes. The regatta control building contains a first aid room, drug testing area, administration rooms, storage rooms and on the upper floor, facilities for judges and the timekeepers, as well as a commentary room. The lake typically hosts an average of 5 major rowing events

630-437: The amount of water they carry, i.e., with " flashy " rivers, and with rivers with weak banks . Braided channels are found in a variety of environments all over the world, including gravelly mountain streams, sand bed rivers, on alluvial fans , on river deltas , and across depositional plains. A braided river consists of a network of multiple shallow channels that diverge and rejoin around ephemeral braid bars . This gives

665-741: The base of the Southern Alps. The Waitaki flows through Lake Benmore, Lake Aviemore and Lake Waitaki , these lakes being contained by hydroelectric dams, Benmore Dam , Aviemore Dam and Waitaki Dam . The Waitaki has several tributaries, notably the Ahuriri River and the Hakataramea River . It passes Kurow and Glenavy before entering the Pacific Ocean. The River lends its name the Waitaki District on

700-668: The canoe Arai-te-uru sank near Moeraki in the 12th century CE. The lake is approximately 4.5 km in length and covers 3.4 square km. It was formed by the New Zealand Ministry of Works as part of the Upper Waitaki Power Project between 1977 and 1981 in a gorge created by the Ōhau River . The gorge was blocked by the building of the Ruataniwha Dam whose crest carries State Highway 8 between Twizel and Omarama . Lake Ruataniwha

735-426: The critical slope for braiding to the discharge and grain size. The higher the discharge, the lower the critical slope, while larger grain size yields a higher critical slope. However, these give only an incomplete picture, and numerical simulations have become increasingly important for understanding braided rivers. Aggradation (net deposition of sediments) favors braided rivers, but is not essential. For example,

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770-548: The flows through Ōhau A do not have to be exactly matched to those through Ōhau B and Ōhau C . Before construction of the dam could start the Ōhau River was diverted by cutting a channel through a low, rocky extension of the Benmore Range and building three diversion gates there which consumed 200,000 cubic metres of concrete. The Ōhau River was diverted in August 1980 so that water passed through Ōhau A and then back down

805-480: The hydroelectric project but instead came about as facilities were constructed as a public service on the instructions of Max Smith, the locally based Project Engineer of the Upper Waitaki Power Project. The rowing course was surveyed, landscaping undertaken and anchors put down for lane markers before the lake was filled. He reached agreement with the Rowing Association that it would fund the building of

840-563: The local community, he took early retirement rather than face charges under the State Services Act. At the time Smith was voicing disagreement with the government's proposals to reduce the Ministry of Works' experienced construction workforce and to disestablish Twizel; all of which may have influenced the official displeasure. The principal access road to the lake was named Max Smith Drive by the local community in his honour while

875-465: The nation. The Waitaki dam was built first, between 1928 and 1934, and without earth-moving machinery, followed by the development of the Aviemore Dam which created Lake Aviemore , and then Benmore Dam which created Lake Benmore . Lake Pukaki was initially dammed at this stage to provide storage and flow control. A small station was also installed on Lake Tekapo , with water taken through

910-671: The original Tekapo (A) station through the Tekapo Canal , to Tekapo B station at the edge of Lake Pukaki. The dam at Pukaki was increased in height. Water from Pukaki is then transferred into the Pukaki Canal which meets the Ohau Canal from Lake Ōhau into Ōhau A station and Lake Ruataniwha . The Ohau Canal continues beyond Lake Ruataniwha to Ōhau B midway along, before emptying through Ōhau C into Lake Benmore. The stations are (commissioned/capacity/annual output): In 2001

945-422: The regatta control building at an estimated cost of NZ$ 75,000. When pressure to complete the building before the official opening of the lake raised the cost to approximately NZ$ 130,000 he used project funds to temporarily bridge the gap until the Rowing Association made full payment. Senior officials in the headquarters of the Ministry of Works alleged this was a misuse of funds. Despite overwhelming support from

980-436: The regions to the north of them). The river is popular for recreational fishing and jetboating . Waitaki translates from southern Māori as "weeping waters" ( wai = "water", taki = "to weep, mourn"). The equivalent in standard (northern) Māori is Waitangi. The river is the site of many hydroelectricity projects. The Waitaki Hydro Scheme , which includes several large dams, is one of the largest hydroelectric projects in

1015-546: The river a fancied resemblance to the interwoven strands of a braid . The braid bars, also known as channel bars, branch islands, or accreting islands, are usually unstable and may be completely covered at times of high water. The channels and braid bars are usually highly mobile, with the river layout often changing significantly during flood events. When the islets separating channels are stabilized by vegetation, so that they are more permanent features, they are sometimes called aits or eyots. A braided river differs from

1050-536: The river banks. They are also found on fluvial (stream-dominated) alluvial fans . Extensive braided river systems are found in Alaska , Canada , New Zealand 's South Island , and the Himalayas , which all contain young, rapidly eroding mountains. Lake Ruataniwha Lake Ruataniwha is an artificial lake in the Mackenzie Basin in the South Island of New Zealand . It was formed in 1977–1981 as part of

1085-466: The river bed. Later that year, downstream of Ōhau A, the river was again diverted, this time away from its natural channel and through the completed gates. An earth dam with gravel shoulders was then built on its upstream and downstream sides. The main dam, which blocks the original river channel, is 240 metres long while an adjoining wing dam is 480 metres. When the dam was completed the diversion gates were closed which, beginning in March 1982, impounded

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1120-414: The river bottom) is essential to formation of braided rivers, with net erosion of sediments at channel divergences and net deposition at convergences. Braiding is reliably reproduced in simulations whenever there is little lateral constraint on flow and there is significant bedload transport. Braiding is not observed in simulations of the extreme cases of pure scour (no deposition taking place), which produces

1155-402: The south side of the river bank. The river's flow is normally low in winter, with flows increasing in spring when the snow cloaking the Southern Alps begins to melt, with flows throughout the summer being rainfall dependent and then declining in the autumn as the colder weather begins to freeze the smaller streams and streams which feed the catchment. The median flow of the Waitaki River at Kurow

1190-406: The water behind the dam up to and over a temporary weir which had been built downstream of Ōhau A. In 1984 the lake was temporarily lowered by 3 metres while this weir was removed to improve the performance of the Ōhau A power station. The diversion gates now function as spillway gates to allow excess water to pass safely through the dam. The lake was officially opened on Saturday 24 April 1982. There

1225-421: Was a weekend event which attracted 7000 spectators with the rowing course hosting a regatta attended by 188 crews and representing 80 South Island rowing clubs. The lake was developed by the Ministry of Works into a major recreational resource for the area with a large number of trees and a holiday park on the lakeside. Ruataniwha is also one of New Zealand's main rowing venues. This was not planned as part of

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