Waikato River

Waikato River
Waikato River passing through Hamilton
The Waikato River system
Country	New Zealand
Basin
Main source	Lake Taupo
River mouth	Port Waikato 0.0 metres (0 ft)
Basin size	13,701 km2 (5,290 sq mi) to Mercer[1]
Physical characteristics
Length	425 kilometres (264 mi)

The Waikato River is the longest river in New Zealand, running for 425 kilometres (264 mi) through the North Island. It rises in the eastern slopes of Mount Ruapehu, joining the Tongariro River system and emptying into Lake Taupo, New Zealand's largest lake. It drains Taupo at the lake's northeastern edge, creates the Huka Falls, and then flows northwest, through the Waikato Plains. It empties into the Tasman Sea south of Auckland, at Port Waikato. It gives its name to the Waikato Region that surrounds the Waikato Plains. The present course of the river was largely formed about 17,000 years ago. Contributing factors were climate warming, forest being reestablished in the river headwaters and the deepening, rather than widening, of the existing river channel. The channel was gradually eroded as far up river as Piarere, leaving the old Hinuera channel high and dry.^[2] The remains of the old river path can be clearly seen at Hinuera where the cliffs mark the ancient river edges. The river's main tributary is the Waipa River, which has its confluence with the Waikato at Ngaruawahia.

The name Waikato comes from the Māori language and translates as flowing water.^[3]

The Waikato River has spiritual meaning for various local Māori tribes, including the large Tainui, who regard it as a source of their mana, or pride. The widely respected marae of Turangawaewae is close to its banks at Ngaruawahia.

For many years Tainui tribe have sought to re-establish their links to the river after the New Zealand Wars (see Invasion of Waikato) and the subsequent confiscations of the 1860s, and are continuing negotiations with the New Zealand government. The Tainui iwi was advised not to bring a case for the river before the Waitangi Tribunal as they would not win. An out of court settlement was arranged and the deed of settlement signed by the Crown and Waikato-Tainui in August 2008 settled the raupatu claim to the Waikato River, although other claims for land blocks and harbours are still outstanding. Waikato-Tainui now have joint management of the river with Environment Waikato.

Origin

The ancestral Waikato River flowed from an ancient lake (Lake Huka) in the centre of the North Island through deep gorges of welded ignimbrite and rhyolite, northward through the Hinuera Valley and Hauraki Basin into the Thames Estuary. It is possible that the river flowed through the Waikato Basin about a million years ago before returning to its Hinuera course. After the huge Oruanui eruption 27,000 years ago pumice was showered all over the North Island to a thickness of 200 metres (660 ft). A new lake was formed—Lake Taupo. The water built up until a new outlet was forced 120 metres (390 ft) above the present level near Waihora Bay. Over the next few thousand years the bed of the river was raised by large amounts of eruption debris. Then the original blocked entry suddenly gave way-the lake level fell 75 metres (246 ft) as about 80 cubic kilometres (19 cu mi) of water and debris poured out in a catastrophic breakthrough flood causing the river to change course near Pairere. The water level dropped quickly and the river stayed in this new course through the Maungatautari gorge and Hamilton Basin. Deposits show that the Waikato River was already in the Waikato Basin 21,800 years ago.^[4]

Course

The Waikato River draining into Huka Falls in Taupo

Port Waikato, the estuary of the River

The river starts as many small streams on the eastern slopes of Mount Ruapehu. The Mangatoetoenui Glacier (once also called the Waikato Glacier) is one of the principal sources.^[5] The southernmost tributary is called the Upper Waikato Stream. The Waipakihi River joins the Waikato from the Kaimanawa Mountains to the west. From the point where the river meets the Waihohonu Stream, down to Lake Taupo, it has been formally named the Tongariro River since 1945.^[5]

The Pouto River joins from Lake Rotoaira to the east. The Tongariro flows northward, with State Highway 1 in parallel, through the town of Turangi, and into the southern side of Lake Taupo.^[6][7] Extensive engineering of lakes, tunnels and canals are used to generate hydroelectric power in the Tongariro Power Scheme.^[8]

The Waikato River flows out of Lake Taupo at the town of Taupo in Tapuaeharuru Bay at the northeast end of the lake. It flows northeast past the town, alongside State Highway 1, to the Huka Falls. State Highway 5 runs more or less parallel to the river as it flows further northeast. About 40 kilometres (25 mi) from the lake, the river flows west and into the southern end of Lake Ohakuri. It exits from the northwest end of that lake and flows west through the small Lake Atiamuri and into the long east–west oriented Lake Whakamaru, with State Highway 30 following its course. It passes northwest through Lake Maraetai and Lake Waipapa, where it is joined by the Waipapa River, then north through Lake Arapuni and into Lake Karapiro. Pokaiwhenua Stream joins the river in Lake Karapiro.^[9][10] Nine hydroelectric power stations at eight dams extract energy from the river between Taupo and Karapiro. All the lakes in this stretch of the river (apart from Lake Taupo) are artificial.^[11]

The river leaves the Volcanic Plateau at Karapiro, where it emerges from the Maungatautari Gorge, and flows northwest into the Waikato Basin, flowing through the towns of Cambridge, Hamilton, and Ngaruawahia.^[12] It is joined by its largest tributary, the Waipa River, at Ngaruawahia. It then flows north through the Taupiri Gorge^[13] to enter the lower Waikato region.^[3] Further north is Huntly and then Meremere, where the Whangamarino and Maramarua Rivers join it. From Mercer, where the Mangatawhiri River joins it, the Waikato flows west and southwest. Just before its mouth at Port Waikato, the Araroa River joins from the north.^[14] Numerous small islands lie in the long, thin delta of the river as it passes through low-lying swampy land between Meremere and the coast, the largest of which is Motutieke Island.

There are also over 40 islands between Ngaruawahia and Tuakau,^[15] depending on the level of the river. Maurea Islands, just south of Rangiriri were subject to a restoration trial to test comparative weed treatments, the main weeds being alder and yellow flag iris.^[16]

In prehistoric times, the Waikato's course has occasionally shifted to flow north into the Firth of Thames and from there into the Hauraki Gulf. The most recent occasion this is known to have occurred ended some 20,000 years ago, although it is possible that it also flowed north more recently, until about 1800 years ago. The river's current course is largely the result of the massive Hatepe (Taupo) volcanic eruption of 180 AD.^[17]

The mean discharge of the Waikato River is 340 cubic metres per second (12,000 cu ft/s), with the highest flows typically occurring in July and August. Specific mean annual floods are low (60-70 L s-1 km-2), and the frequency of events with greater than 3 times the median flow is 0.4 events / year, due to flow regulation and groundwater storage in pumice.^[18]

Human usage

A boat on Lake Karapiro

As well as being a water and recreation resource, the river was historically a critical communications and transport link for the communities along it.^[19] Taupo, Mangakino, Cambridge, Hamilton, Horotiu, Ngaruawahia, Huntly, Hampton Downs, Meremere, Waiuku and Port Waikato are on or close to it. The Waikato River in Hamilton is frequently used by rowers, kayakers and powered pleasure craft. Water-skiers and jet skis have zones outside the city limits where they can be used. There are two ramps for launching boats – one in Pukete and the other just north of the traffic (Bridge St) bridge.

The river was of military importance in the land wars between New Zealand and rebel Māori Kingitanga forces during 1863–64 and significant battles were fought. Three shallow draft gunboats were designed in New Zealand and built in Sydney in kitset form. In addition locally sourced barges were rebuilt with steel plating to carry troops and supplies. In support of these wars, New Zealand developed its first "navy", the Waikato Flotilla, run by an Australian Francis Cadell who was recognised for his spendid service by the presentation by the New Zealand government of a gold watch and diamonds. A cemetery containing the graves of the British military dead can be found at Rangiriri opposite the hotel, shops and cafe.

A ferry service along part of its length was for years conducted by Caesar Roose,^[20] several of whose descendants still live beside it. In 1924 a Cambridge to Port Waikato excursion was being run 2 or 3 times a year, taking 12 to 14 hours downstream and a few hours longer upstream.^[21] Several of the old steamers remain under, or beside the river,^[22] including the Rawhiti (built 1925)^[23] and Freetrader on the west bank just south of Mercer.^[24]

Electricity generation

The Ohakuri Dam midway between Taupo, Rotorua and Hamilton

The Huntly Power Station is cooled by the Waikato River

The Waikato's first hydro-electric power station was the Horahora Power Station, now located under the Horahora bridge deep beneath the surface of Lake Karapiro. Horahora was built to supply electricity for the Martha gold mines at Waihi.^[25]

The river has a series of eight dams and nine hydro-electric power stations that generate electricity for the national grid. These were constructed between 1929 and 1971 to meet growing demand for electricity.

The power scheme begins at Lake Taupo, which has control gates to regulate the flow of water into the river. Once released through the gates it takes over 18 hours for the water to flow to the last power station at Karapiro.^[26] On its journey downstream it passes through power stations at Aratiatia, Ohakuri, Atiamuri, Whakamaru, Maraetai, Waipapa, Arapuni and Karapiro.

Approximately 4000 gigawatt hours (GWh) of electricity is generated annually by the scheme, which is around 13% of New Zealand's total electrical generating capacity.

The river also provides cooling water for the coal/natural gas fired thermal power station at Huntly. The power station uses river water as a cooling medium for the old steam units, which means that large quantities of warm water is returned to the river. To limit environmental impacts, conditions are imposed by its resource consent, specifying the quantity of water that can be removed by the station along with the maximum temperature of the water when returned to the river, 25 °C (77 °F). These conditions mean that output of the older steam units can be restricted, especially on very hot summer days. In 2006, a cooling tower was installed. This allows one 250 MW unit to run at full load even during such times.^[27]

Recreation

The Waikato is renowned among whitewater kayaking enthusiasts, specifically for the Full James rapid located north of Taupo. The Full James was the site of the 1999 World Whitewater Championships, as well as the pre-World event the year before. The lower Waikato is also popular amongst duck shooters.

Lake Karapiro (an artificial lake) is regarded as one of New Zealand's best rowing venues. The World Rowing Championships in 1978 and 2010, and the 1950 British Empire Games were hosted at Karapiro.

The cycleway was extended to link up with Hamilton's riverside path in 2014. The 2001 Horotiu bridge replaced one built in 1924.

Boosted by New Zealand Cycle Trail funding, construction is ongoing (as of 2009) on completing the Waikato River Trails, a 100-kilometre (62 mi) series of connected river cycling trails in the South Waikato.^[28]

Te Awa River Ride follows over 50 km (31 mi) of the river from Horahora, near the end of the Waikato River Trails, via Cambridge and Hamilton to Ngaruawahia. Completion is planned for 2017.^[29] North of AFFCO at Horotiu,^[30] the route includes the longest cycle bridge in the country, a 140 m (150 yd) long cable network arch bridge.^[31]

Te Araroa Trail (the river walkway linking the far north with the far south of the country) follows the Waikato for most of its 80 kilometres (50 mi) between Mercer and Hamilton.^[32] The River Trail has five sections totalling 100 kilometres (62 mi) open to both walkers or bikes. The river trail runs between Lake Karapiro and Aratiatia. It opened in 2011.

The Wairere currently operates from Aratiatia to Ohakuri on the Waikato River.^[33] The section of the river that flows through Hamilton has the most diverse river traffic with many schools and clubs using rowing skiffs. Rowing races are also held on the river. Jet skis are confined to the city margins because of their noise. Power boats regularly use the river, including manufacturers and boating shops testing and demonstrating boats, especially in summer. In addition there are numerous kayaks and a few waka.

Ecology

Species

The Waikato River and its hydro lakes are home to at least 19 types of native fish and 10 types of introduced fish.^[34] The introduced species include rainbow and brown trout providing what has been called "the finest fly-fishing in the world".^[35] Other introduced species, like the carp and mosquitofish, have become major pests.

Environmental issues

A tributary stream in the Waitomo District showing agriculture-induced erosion

The large catchment area of the Waikato River is highly fertile farmland, so intensive agriculture is present. Due to the agricultural activity within the catchment significant agricultural pollution is leached into groundwater and contained in the runoff. The mismanagement of nitrogen fertilizer and effluent spreading practices in dairy farming is seen as the major causes of this pollution. Since 2000 Environment Waikato has joined with conservation minded farmers to bring about more efficient and scientific use of fertilizers.

The removal of the native vegetation throughout the catchment to accommodate the increasing demand for farmland has contributed to the silting-up of the river with loose soils from eroded farmland, although most of the silting is due to the construction of the many hydrodams. In its pre-1930s wild state, the silt was flushed from the river every winter by flood surges. The remnants of these can be seen in the silt channels carved out of what is now St Andrews golf course, adjacent to the river in Hamilton.

Arsenic is also a major problem and the concentration reaches 0.035 grams of arsenic per cubic metre in places,^[36] greatly exceeding the WHO provisional guideline of 0.01 grams of arsenic per cubic metre.^[37] The majority of arsenic in the Waikato River comes from the Wairakei Geothermal Power Station. The amount of arsenic gradually declines as the river flows northwards and is at its lowest at the Waikato River Heads.^[38]

Since 2002, around 75 million litres (20,000,000 US gal) of water a day has been drawn from the river at Tuakau, treated and pumped along a 38-kilometre (24 mi) pipe north to Auckland, where it is mixed with local water.^[39] This met 8% of Auckland's water needs in 2010/11.^[40] In December 2012 capacity was increased to 125 million litres (33,000,000 US gal), and in 2013 work started to increase it to 150 million litres (40,000,000 US gal).^[41] The treatment plant meets New Zealand's 2000 drinking water standards according to Water Care NZ. This is equal to or better than the A standard for Auckland's other water supplies.

Slightly-modified human wastes are pumped into the river downriver of several towns. Hamilton city has one of the most modern water treatment systems in the world following a 2003 report by GHB water consultants. In 2007 $22 million was spent upgrading the existing intake station south of the city at Riverlea. This will meet the cities demand until 2016. Waste water in its untreated state is 99.9% water and 0.1% other matter. A series of sophisticated machines produce clean water of a high standard getting rid of bad tastes odours and toxins to meet the upgraded NZ water standards. The Pukete 2 project which started in 2002 will upgrade the plant in a series of stages costing $24 million.

A further issue is industrial and metropolitan waste from early-established landfills and waste-emitting factories on the banks of the river. These include an unlined waste dump at Horotiu, just downriver from Hamilton, whose leachates include persistent organic pollutants such as dieldrin in quantities toxic to freshwater marine life. The 2002 GHD report saw new regulations put in place to make industries comply with a new bylaw which stops hazardous substances entering the water system at all according to the HCC website. In 2002 dead eels were found in a tributary of the river when a container of pesticides and other chemicals was apparently illegally dumped. The chemicals were diluted when they entered the much bigger Waikato River. The harmful effect was temporary.

See also

• List of rivers of New Zealand
• List of rivers of New Zealand by length

References

External links

• Waikato River Basin Flow Rates and Rainfall.
• Hamilton City Council's Waikato River webcam

Coordinates: 37°22′10″S 174°42′29″E / 37.3694°S 174.708°E / -37.3694; 174.708