FMU History and Land Use
Climate
The climate of the Wairau FMU is characterised by a wet climate for those tributaries located on the north bank of the Wairau Valley, while the south bank tributary catchments have a dry climate. There is also a distinct west to east rainfall gradient from the mountainous western upper catchment which can experience high mean annual rainfalls from 1,500 to 2,500mm, down to the east coast where mean annual rainfall can be as little as 650mm. Summers in Blenheim are warm and dry; while winters are generally sunny, frosts are common. Inland temperatures are generally several degrees cooler and the number of frost days increases.
Geology and Soils
Tectonic activity has had a major influence on the geology of the Wairau. Northwest tilting of land between the Wairau and Awatere faults has resulted in the main tributaries of the Wairau River being on the southern side of the Wairau Valley. Most of the geology in the catchment is greywacke and argillite with the lower reaches having extensive alluvial deposits laid down by the Wairau River and its tributaries from erosion of the inland mountain ranges during glacial periods. To the south-eastern side of the FMU are the Wither and Redwood Hills which were also formed from tectonic movements consisting of underlying gravel conglomerates topped by extensive wind-blown Wairau loess greywacke, which is highly erodible.
Soils on the Wairau Plain reflect this geological history with loess and more developed soils on the older alluvium terraces, with less well-developed soils on the younger redeposited terraces. The lower valley also contains organic floodplain deposits. To the east of State Highway 1, the soils occur on geologically recent sand dunes, gravel beach ridges, alluvium, and saline estuarine deposits.
Bodies of Water
Upper Wairau River
The Wairau River is some 170 kilometres long, rising in the Spenser Mountains to the south of St Arnaud at a height of over 2,000 metres. Initially, the river flows north for around 50 kilometres before flowing northeast along the Wairau Fault for the remainder of its length and reaching the sea at Cloudy Bay on the edge of the Cook Strait. In its upper reaches, it is confined in a gorge with rapids. As the valley widens, the river becomes increasingly braided in its middle reaches. These middle reaches of the Wairau are known to be of importance for the recharge of the Wairau Aquifer and are the subject of a five-year study into braided rivers being undertaken by several councils and Lincoln Agritech.
In its lower reaches below the State Highway 1 bridge, the river divides into two. The tidal, meandering main channel flows in a south-easterly direction, past Grovetown Lagoon, before feeding the Wairau Lagoon area and discharging into the sea at the Wairau Bar. The second channel flows through the Wairau Diversion, built in the 1963 to reduce flood levels, which provides a more direct route east to the coast.
Southern Wairau River Tributaries
Branch River
The first major southern tributary of the Wairau River is the Branch River, which flows nearly 40 kilometres north through mountainous country to its confluence with the Wairau River. Part of the Branch River’s catchment includes the Leatham River, which is of a similar length. Both rivers have headwaters with subalpine habitats, being replaced by beech forests until close to their confluence with the Wairau where plantation forestry occurs. Monitoring at the Branch River has shown it has the second-highest water quality in the region. The lower Branch River is the location of one of the hydro-electric power stations in the region with water diverted from the river and into Lake Argyle, which was constructed as a storage reservoir in the early 1980s. The water passes through the two power houses before joining the Wairau River through a canal system.
Between the Branch River and the next major southern tributary of the Wairau, the Waihopai River, there are several small tributaries including the Wye River, Hillersden Stream and the Marchburn River. These are generally characterised by steeper gradient headwaters in the hill country, which decrease as the tributaries make their way across the Wairau Plain to join with the Wairau River.
The largest southern tributary of the Wairau River is the Waihopai River. Rising towards the southwest of the FMU, near the Acheron Saddle, it flows for 60 kilometres in a northeast direction to join the Wairau River just west of Renwick. The river is similarly confined by areas of gorges in its upper reaches but becomes braided in its lower reaches. The Spray River and the Avon River are significant tributaries of the Waihopai, joining it from the eastern side of the catchment. The Waihopai River and its tributaries experience varied rainfall across their catchments, which can be over 2,000mm in the headwaters to less than 800mm in the lower reaches. This results in variable river flows and high turbidity during high flows. The river is also known for the first hydro-electric scheme in Marlborough, which began operation in 1927 and still operates today. Due to the active erosion by the river, the original lake that built up behind the dam is now filled with gravel and shingle with regular maintenance required to keep the sluice gates free of material. The dam forms a barrier to sediment movement to the lower Wairau River catchment, contributing to falling riverbed levels there.
Taylor River near Blenheim CBD
East of the Waihopai, the remaining southern Wairau tributaries include the dry southern valley catchments of the Omaka, Fairhall and Taylor Rivers which flow northeast from headwaters in the hills across the Wairau Plain. All these rivers are characterised by significant dry periods each year due to water loss from natural groundwater recharge. These tributaries flow into the Ōpaoa River, which flows in an easterly direction through the northern part of Blenheim before joining the Wairau River close to the Wairau Lagoons. The Taylor River is also worth a separate mention, as in 1965 the Taylor Dam was built on the river and remains the largest earth flood protection dam in New Zealand. Prior to the dam, Blenheim was often flooded due to the river levels rising rapidly during heavy rain events.
The lower Wairau Plain also has many springs that are the main conduit for groundwater leaving the area. The system is highly complex and has been highly modified since European settlement. Examples of these include Spring Creek, which is the largest emergence of groundwater in the Wairau Plain where crystal-clear water emerges in a series of springs near Hammerichs Road. The more southerly expression of these springs form the base flows for the Taylor River upstream of the High Street Bridge.
The Tuamarina River is a tributary of the Wairau River which flows south from its origins on the slopes of Mt. Freeth, near Picton. The valley that contains the Tuamarina River is also known as the Waitohi Valley.
Northern Wairau River Tributaries
Rainbow River
On the northern side of the Wairau River, there are also several significant tributaries. The Rainbow River is the mostly westerly of these, rising to the north of the Wairau River and joining it just upstream near the turn off to Rainbow Ski Field Road. The next most significant northern tributary is the Goulter River, which has the highest water quality in the region with a catchment that is highly natural. It rises in the Richmond Ranges near Lake Chalice, which was formed by a landslip around 2,000 years ago and dammed the river. The lake is around 2 kilometres long and 200m wide and has no outlet. However, water seeps through the landslip and into the river, which flows counterclockwise around Mount Patriarch to join the Wairau River.
Between the Goulter River and the confluence of the Waihopai with the Wairau River, there are several north bank rivers flowing from the Richmond Ranges over short distances into the Wairau. These include Top Valley Stream, Timms Creek, Fabians and Bartletts Creek, and the Ohinemahuta Creek. The upper catchments of these rivers are dominated by native bush with increasing plantation forestry on lower slopes the further east travelled.
There are three main rivers on the lower banks of the Wairau Valley—Are Are Creek, Waikakaho River and Tuamarina River. All three of these rivers have catchments that are dominated by plantation forestry on the hills and pastoral farming in the valleys. The Tuamarina River runs through Para Swamp, a large wetland that contained kahikatea and totara in pre-colonial times, which supported large numbers of birds and fish as important Māori food sources. Due to its geomorphology, the swamp was impractical to drain and so survives today. However, willows planted to stop flooding resulted in the decline of native habitat. In recent years, there have been efforts to restore native vegetation with Fish and Game poisoning most of the willows.
Flora and Fauna Habitats
The Wairau FMU supports many areas for riparian, fish, bird, and invertebrate habitats. Examples include black flounder in Are Are Creek, along with common, redfin and upland bully, inanga, lamprey, longfin and shortfin eels and koura. Dwarf galaxias and their spawning areas are found in Barletts Creek and alpine areas; dwarf and northern flathead galaxias are found in the Branch River. The springs support banded and giant kokopu, freshwater mussels and the largest population of the indigenous Potomogeoton cheesemannii (red pondweed) on the Wairau Plains. The upper Wairau areas provide a feeding habitat for black-fronted terns, while the coastal Wairau provides bittern and waterfowl habitats. Within Lake Chalice is a scientifically important landlocked population of kaoro. Grovetown Lagoon provides a substantial bird habitat for the grey duck, Australasian shoveler, New Zealand scaup, paradise shelduck, kotuku, pukeko and white-faced heron. The Northbank rivers also support torrentfish and bluegill bully, while the lower Ōpaoa has yelloweye and grey mullet.
Much of the upper Wairau catchment is covered in beech forests. However, little native vegetation remains on the Wairau Plains. One significant area is the Rārangi wetlands, which are a series of wetland-filled troughs situated between dry post-glacial beach ridges parallel to the coast. These extend inland from the coast for some four kilometres, and a range of specialist plants and animal communities are associated with both the wet and dry environments.
Land Use and Cover
Prior to human settlement, the Wairau FMU area was a thriving ecosystem containing a broad range of native land covers. This ranged from alpine grasses in the highest areas through to broadleaf Totara and podocarp forests in the hill lands, through to a lowland complex of wetlands, swamps, and lagoons on the plains which were cut by multiple waterways. Native forest and ferns would have also been present in the lowland areas.
The earliest Polynesian settlers are estimated to have landed at and occupied the Wairau bar from about 1300AD. Given the abundant natural resources and food supply, the Wairau area was well populated by early māori, from both direct settlement from Polynesia and domestic movement south from the North Island. A wide range of food options were available, including moa, seals, tuna, and a wide range of fish and other bird species. Carbon dating and oral history shows that fire was used for activities including vegetation clearance and hunting at this time.
In the early 1840s, Europeans had begun to arrive in New Zealand. The Wairau Plains were a substantial area of flat land at the top of the South Island and pressure to survey land led to conflict, known as “The Wairau Incident”, between the Māori owners and the New Zealand Company who were undertaking land surveying. With increasing populations, clearing of land by fire and drainage of the wetlands/swamps, grasslands became a more dominant part of the landscape. Pastoral sheep farming became the major industry in the late 1800s, particularly with the advent of refrigerated ships at the turn of the 20th century and the rise of the meat industry.
Blenheim was founded in 1850. In the early days, it was known as Beavertown as both the Wairau floodplain and the town experienced at least one damaging flood every decade since European settlement. In 1855 an earthquake in the North Island resulted in sufficient subsidence of the Wairau Lagoons to enable navigation of the lower Wairau and Ōpaoa Rivers by ships leading to substantial trading with the North Island. Despite intensive river work carried out from 1877 to 1902, damaging floods continued until the Wairau River Board was established in 1920s. The board began a comprehensive plan for the rivers of the floodplain, raising stopbanks, widening the floodway and groyne construction. In 1956 to 1989 the Marlborough Catchment Board took over and further works were undertaken, including the Taylor Dam, the Wairau Diversion and extensive stopbank upgrading.
Cropping was prominent in the region with oats, barley, and peas. During the war years, flax was grown and milled to support the linen trade. After the war, land use on the Wairau Plains began to diversify with further cropping, market gardening and orcharding of pip and stone fruits. The 1950s saw a resurgence of pastoral farming with wool becoming profitable and dairying increasing.
One pioneer of viticulture in Marlborough was David Herd, who planted a small vineyard in Fairhall in 1873. A local farm manager, Herd grew muscatel grapes and made his own wine, continuing until his death in 1905. A man before his time, Herd set the trend which was picked up by others from 1880 onwards – but not in significant commercial developments until the 1970s.
In 1973, the first vineyard signalling the new wave of viticulture was planted by Montana owner Frank Yukich in Fairhall with viticulturalist Wayne Thomas, who recognized the terroir of the area was ripe for viticulture conversion. Montana purchased 4,000 acres in the previously undeveloped wine region and a movement was born.
Since that time, there has been a steady change of land use on the Wairau Plain from orcharding, market gardening, and pastoral farming to viticulture. Land use change has been rapid – not only the physical conversion of the land but also the development of wineries, brands, labels, and service industries to complement the sector.
Blenheim is the largest urban centre in Marlborough and is located towards the eastern side of the Wairau FMU. To the west are the settlements of Renwick and Wairau Valley, and to the north are the settlements of Grovetown, Spring Creek, Tuamarina and Koromiko situated along State Highway 1 towards Picton. There are also some smaller residential enclaves at Rārangi, Fairhall and Woodbourne. The airport and RNZ Air Force Base Woodbourne is located between Renwick and Blenheim in the centre of the Wairau Plain which holds a significant number of Base personnel. There is also a dispersed rural population located close to the major roads along the Wairau and Waihopai Valleys and scattered across the Wairau Plain. These rural populations become sparser moving west up the valleys. South of Blenheim, off State Highway 1, are the industrial areas of the Riverlands and Cloudy Bay Business Parks where most of the industry is located for the region.
There has been significant land use change within the last 30 years in the area. The rapid expansion of viticulture in the Wairau is shown on the graph below, including upper and lower areas.
The below land use map provides a contextual image of current land use:
The below chart shows a graphic illustration of land cover change in the combined Wairau and Omaka catchments between 1996 (inner ring) and 2018 (outer ring). Together, these areas represent the majority of the Wairau FMU and the chart provides a high level representation of the changes over this time. We can see a large increase in viticulture, smaller increase in forestry, and a reduction in grassland. The urban/non vegetated area has also increased slightly.
Māori History in the Area
The council has an ongoing work stream with local iwi to identify their visions, values, and aspirations for freshwater in the FMU. These will be collated with views from the wider community.
