Lake Wahapo ( mi, Wahapako) is a small glacial lake in South Westland, New Zealand, within the
Westland Tai Poutini National Park
Westland Tai Poutini National Park is a national park located on the western coast of New Zealand's South Island. Established in 1960 as Westland National Park to commemorate the centenary of the European settlement of Westland District, it ...
and near the township of
Whataroa
Whataroa is a small township in southern Westland on the West Coast of New Zealand's South Island. It is located on the western bank of the Whataroa River, with the village of Te Taho on the other side. passes through Whataroa on its route from R ...
. It was a traditional mahinga kai (food-gathering place) for local
Māori
Māori or Maori can refer to:
Relating to the Māori people
* Māori people of New Zealand, or members of that group
* Māori language, the language of the Māori people of New Zealand
* Māori culture
* Cook Islanders, the Māori people of the C ...
.
State Highway 6 skirts the lake's southern shore. The lake discharges to the
Ōkārito River
The Ōkārito River is a river of the West Coast Region of New Zealand's South Island. It flows northwest from the northern end of Lake Mapourika, reaching the Ōkārito Lagoon 15 kilometres west of Whataroa.
See also
*List of rivers of New Zeal ...
via a small hydroelectric power station commissioned in 1960. The ecology of the lake has altered considerably since 1967, when the
Waitangitāhuna River
The Waitangitāhuna River (formerly called the Waitangitaona River) are two rivers in the West Coast, New Zealand, West Coast region of New Zealand's South Island. It was a single river until an Avulsion (river), avulsion in March 1967, when it b ...
changed course to flow into the lake.
Geography
Lake Wahapo is located about southwest of
Hokitika
Hokitika is a town in the West Coast region of New Zealand's South Island, south of Greymouth, and close to the mouth of the Hokitika River. It is the seat and largest town in the Westland District. The town's estimated population is as of .
...
, and northwest of
Franz Josef / Waiau
Franz Josef / Waiau is a small town in the West Coast region of the South Island of New Zealand. Whataroa is to the north-east, and the township of Fox Glacier is to the south-west. The Waiho River runs from the Franz Josef Glacier to the south ...
. It lies between the settlements of Whataroa and
Ōkārito
Ōkārito is a small coastal settlement on the West Coast of New Zealand's South Island, southwest of Hokitika, and from . It is built at the southern end of the Ōkārito Lagoon at the mouth of the Ōkārito River. The settlement of The Forks ...
, about from each. The lake is long, has a maximum width of , and covers an area of about . State Highway 6 follows the southern shore of the lake for about , making it easily accessible to travellers.
Like many of the lakes of South Westland, Lake Wahapo was formed following the retreat of local glaciers at the end of the
Last Glacial Period, around 12,000 years ago. The lake occupies an unfilled lobe of a former
glacial trough
U-shaped valleys, also called trough valleys or glacial troughs, are formed by the process of glaciation. They are characteristic of mountain glaciation in particular. They have a characteristic U shape in cross-section, with steep, straight s ...
and is enclosed by
moraine
A moraine is any accumulation of unconsolidated debris (regolith and rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a glacier or ice shee ...
walls to the north, south and west. The eastern end of the lake is bounded by a gently sloping
alluvial fan
An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...
, forest, and
pakihi
Pakihi or pākihi is a vegetation association unique to the West Coast of the South Island of New Zealand, characterised by flat boggy land with infertile, waterlogged soil on which only rushes, ferns, moss, and mānuka grow.
Name
The Māor ...
.
A flood in March 1967 caused the
avulsion of the
Waitangitāhuna River
The Waitangitāhuna River (formerly called the Waitangitaona River) are two rivers in the West Coast, New Zealand, West Coast region of New Zealand's South Island. It was a single river until an Avulsion (river), avulsion in March 1967, when it b ...
, with the result being that the Waitangitāhuna now flows into Lake Wahapo, from its previous course. Prior to that time, the lake had dark, peaty waters that provided reflections of the
kahikatea
''Dacrycarpus dacrydioides'', commonly known as kahikatea (from Māori) and white pine, is a coniferous tree endemic to New Zealand. A podocarp, it is New Zealand's tallest tree, gaining heights of 60 m and a life span of 600 years. It was firs ...
forest on the lake's shore. However, since the Waitangitāhuna changed course, Lake Wahapo has been transformed from an organic-dominated lake into a turbid water body. The Waitangitāhuna carries large volumes of sediment, and a
delta
Delta commonly refers to:
* Delta (letter) (Δ or δ), a letter of the Greek alphabet
* River delta, at a river mouth
* D (NATO phonetic alphabet: "Delta")
* Delta Air Lines, US
* Delta variant of SARS-CoV-2 that causes COVID-19
Delta may also re ...
has formed at the eastern end of Lake Wahapo. Between 1967 and 2008, the delta prograded about into the lake, and in 2008 the delta plain covered with an estimated average depth of . In 2012, it was estimated that in about 300 years Lake Wahapo would be completely filled with sediment. The increased volume of water entering Lake Wahapo following the avulsion caused the average lake level to rise by about .
History
Local
Māori
Māori or Maori can refer to:
Relating to the Māori people
* Māori people of New Zealand, or members of that group
* Māori language, the language of the Māori people of New Zealand
* Māori culture
* Cook Islanders, the Māori people of the C ...
called the lake ''Wahapako'', after one of the daughters of a
rangatira
In Māori culture, () are tribal chiefs, the hereditary Māori leaders of a hapū. Ideally, rangatira were people of great practical wisdom who held authority () on behalf of the tribe and maintained boundaries between a tribe's land and that ...
, Kārito, for whom Ōkārito is named. Wahapako was a traditional mahinga kai (food-gathering place) for local Māori, who would come to the lake to gather
longfin eels. The now-extinct
New Zealand grayling
The New Zealand grayling (''Prototroctes oxyrhynchus'') is an extinct species of fish that was endemic to New Zealand. It was known to the Māori by many names, including pokororo, paneroro, kanae-kura, and most commonly, upokororo. The variety o ...
(''Prototroctes oxyrhynchus''), known to Māori as ''upokororo'', was an important food source for Māori, and were abundant in the area; the outflow from Lake Wahapo was one of the last areas in which the species was reliably recorded.
![Bush sawmill near Lake Wahapo 1909](https://upload.wikimedia.org/wikipedia/commons/a/ae/Bush_sawmill_near_Lake_Wahapo_1909.jpg)
From the 1890s, native forests on the West Coast were exploited for their timber, with kahikatea and
rimu
''Dacrydium cupressinum'', commonly known as rimu, is a large evergreen coniferous tree endemic to the forests of New Zealand. It is a member of the southern conifer group, the podocarps.
The Māori name ''rimu'' comes from the Polynesian ...
being particularly sought after in South Westland. Timber mills operated in the Lake Wahapo area, with one shipment of about of
mataī
''Prumnopitys taxifolia'', the mataī ( mi, mataī) or black pine, is an endemic (ecology), endemic New Zealand coniferous tree that grows on the North Island and South Island. It also occurs on Stewart Island/Rakiura (47 °S) but is uncommon ...
being sent from the Lake Wahapo Mill to Wellington in 1939 for the
New Zealand Centennial Exhibition
The New Zealand Centennial Exhibition took place over six months from Wednesday 8 November 1939 until 4 May 1940. It celebrated one hundred years since the signing of the Treaty of Waitangi in 1840 and the subsequent mass European settlement of ...
buildings.
In 1960, a hydroelectric power station was commissioned at Lake Wahapo, utilising the outflow from the lake, and discharging it into the
Ōkārito River
The Ōkārito River is a river of the West Coast Region of New Zealand's South Island. It flows northwest from the northern end of Lake Mapourika, reaching the Ōkārito Lagoon 15 kilometres west of Whataroa.
See also
*List of rivers of New Zeal ...
. The scheme was built at a cost of £40,000 to provide reliable electricity supply to about 90 customers in the Whataroa area, and included of 11,000-volt transmission lines. The local territorial authority at the time, the
Westland County Council
Westland County, also known as County of Westland, was a local government area on the West Coast of New Zealand's South Island. It existed from 1868 to 1873, and then from 1876 until 1989. In its first incarnation, it constituted the government f ...
, levied a special
rate
Rate or rates may refer to:
Finance
* Rates (tax), a type of taxation system in the United Kingdom used to fund local government
* Exchange rate, rate at which one currency will be exchanged for another
Mathematics and science
* Rate (mathema ...
to fund the project. The station used a generator set that had previously been used during the construction of the
Homer Tunnel
The Homer Tunnel is a 1.2 km (0.75 miles) long road tunnel in the Fiordland region of the South Island of New Zealand, opened in 1953. New Zealand State Highway 94 passes through the tunnel, linking Milford Sound to Te Anau and Queenstown ...
. In 1990, the scheme was redeveloped, resulting in an increased maximum generation capacity of 3.1MW, and an average annual output of 15.3GWh.
On 29 March 1960, the scenic reserve around Lake Wahapo was included in the gazetting of the new
Westland National Park
Westland Tai Poutini National Park is a national park located on the western coast of New Zealand's South Island. Established in 1960 as Westland National Park to commemorate the centenary of the European settlement of Westland District, it co ...
(now Westland Tai Poutini National Park), New Zealand's ninth national park.
Ecology
The ecology of Lake Wahapo was severely affected by the avulsion of the Waitangitāhuna River in 1967. The river carries large amounts of fragmented schist rock and debris from a massive slip in the headwaters of the river's catchment. The river's new course after the avulsion was across an ancient alluvial fan and through a stand of kahikatea (''Dacrycarpus dacrydioides'') at the northeastern end of the lake. Heavier fractions of the debris are deposited before reaching the lake, but the lighter elements are carried to the lake. Silt was quickly deposited in the kahikatea forest, burying the low understory vegetation and causing widespread mortality of the trees at the head of the lake. Within three or four years, the dying trees were subject to fungal attack and could not be salvaged for timber. In areas where less silt was deposited (less than about deep), only a few trees died, and those that survived produced
adventitious root Important structures in plant development are buds, shoots, roots, leaves, and flowers; plants produce these tissues and structures throughout their life from meristems located at the tips of organs, or between mature tissues. Thus, a living plant a ...
s, allowing them to adjust to the saturated silt.
Tōtara
''Podocarpus totara'' (; from the Maori-language ; the spelling "totara" is also common in English) is a species of podocarp tree endemic to New Zealand. It grows throughout the North Island and northeastern South Island in lowland, montane and ...
(''Podocarpus totara''),
miro (''Prumnopitys ferruginea''),
mountain horopito (''Pseudowintera colorata''),
patē (''Schefflera digitata''), and
mikimiki (''Coprosma rotundifolia'') also survived by producing adventitious roots. Mosses, herbs and smaller shrubs were completely destroyed where there was initial silt deposition, but have recovered in areas where deposition has ceased.
Other plant species that have been recorded around Lake Wahapo include:
whekī-ponga (''Dicksonia fibrosa'') at the eastern end of the lake; sedge (''Isolepis reticularis'') and ''
Coprosma propinqua
''Coprosma propinqua'' is a New Zealand plant of the genus ''Coprosma'' in the family Rubiaceae. Its Māori name (in common New Zealand usage) is ''mingimingi'', a name which is also applied to closely related species such as '' C. dumosa'', '' ...
'' × ''
robusta
ROBUSTA (Radiation on Bipolar for University Satellite Test Application) is a nano-satellite scientific experiment developed by the University of Montpellier students as part of a Centre National d'Études Spatiales (CNES) call for student projects ...
'' in swampy areas; and ''
Ranunculus flammula
''Ranunculus flammula'', the lesser spearwort, greater creeping spearwort or banewort, is a species of perennial herbaceous plants in the genus ''Ranunculus'' (buttercup), growing in damp places throughout the Boreal Kingdom. It flowers June/Jul ...
'' on the flat at the head of the lake and in swamp pools.
Since 1967, the silt-laden water of the Waitangitāhuna River has caused an increase in the turbidity of Lake Wahapo, and a concomitant reduction in light penetration. The much larger volume of water entering the lake than previously has increased mixing in the lake, resulting in an almost uniform water temperature from the surface to the bottom of the lake. A further consequence is a lower abundance of plankton in Lake Wahapo compared to nearby
Lake Mapourika
Lake Mapourika is located on the West Coast of New Zealand's South Island. It lies north of Franz Josef Glacier, and the out-flowing Ōkārito River drains it into the Ōkārito Lagoon. It is the largest of the West Coast lakes, a glacier form ...
.
Brown trout
The brown trout (''Salmo trutta'') is a European species of salmonid fish that has been widely introduced into suitable environments globally. It includes purely freshwater populations, referred to as the riverine ecotype, ''Salmo trutta'' morph ...
and
salmon
Salmon () is the common name for several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the family (biology), family Salmonidae, which are native to tributary, tributaries of the ...
, both introduced species, are found in Lake Wahapo. The introduction of trout to New Zealand rivers has been cited as one of the possible factors in the extinction of the New Zealand grayling.
Gallery
File:Lake Wahapo - panoramio.jpg
File:Adams Range.jpg
File:Lake Wahapo - panoramio (1).jpg
File:Ōkārito + Whitebaiting • Nimmo • MRD 16.jpg
File:Ōkārito + Whitebaiting • Nimmo • MRD 14.jpg
Notes
References
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{{Westland landforms
Wahapo
Wahapo