Dunstan Rohe (Area)

Exotic grasslands, primarily for farming, cover 37% of the rohe and 23% is conservation land. Sheep and beef are the dominant farming type (45%), followed by mixed livestock farming including sheep, beef, and deer (15%), and sheep (5%). Dairy, nurseries, vineyards, and orchards occur on 1% of land area.

Notable trends in land use change over the past 30 years have been an increase in conservation estate by 293%, urban development by 108% and nurseries/vineyards/orchards by 33%. Dry-stock farming has decreased by 25%, although still the most common land use in the Dunstan area.

Most frequent soil types are Brown (53%), Pallic (29%) and Semi-arid (11%). Most Brown and Semi-arid soils are moderately or well-drained and permeable. However, in some areas, Brown soils have poor drainage, including parts of the Lindis, Nevis and Luggate catchments. Semi-arid soils extend from the Lindis river catchment down to Bannock Burn. Raw soils occur in 4% of the rohe in alpine rock areas where erosion is active: for example, Centaur peaks and Mount Aurum.

Dunstan Rohe land use summary

Climate in the Dunstan Rohe is very diverse and includes some of the wettest, driest, warmest, and coldest places in New Zealand. Annual rainfall in the headwaters of the Shotover River is more than 3000mm per year, while in parts of the Upper Clutha Mata-au Valley, rainfall is less than 400mm per year. There is a steep rainfall gradient from west to east, with Shotover headwaters only about 50 km from the low-rainfall Upper Clutha Mata-au area.

Air temperatures from -10oC to 36oC have been recorded in the Upper Clutha Mata-au Valley. Temperatures of less than -10oC are likely in the headwaters of the Shotover River, where it is close to permanent snow and ice.

There is abundant water in rivers where rainfall or snow melt is plentiful, including the Shotover, Kawarau and Clutha Mata-au Rivers headwaters. However, much less water in smaller rivers and streams in the Upper Clutha Mata-au Valley, with only about 10% of the rainfall in the Shotover headwaters.

Very little water is taken from the Shotover and Nevis Rivers, but there is significant water use in the Upper Clutha Mata-au Valley from the Clutha Mata-au river, and the Hāwea and Dunstan lakes. Here, irrigation is the lifeblood of farming, and some streams run dry in summer.

Water quality is generally very good. However, there is pressure on water quality in drier catchments where high water use, or high population growth rates occur. ORC monitors water quality and ecology of rivers and streams. When the results are combined, they can show the health of a river or stream, and long-term data is analysed to show trends in water quality over time. Many sites in this rohe have been monitored by ORC for less than five years, so current water quality state and trends are interim results.

Six of the sixteen river sites monitored did not meet the required standard for at least one measurement, according to the National Policy Statement for Freshwater Management (2020). Upper Cardona, Quartz Reef Creek, Mill Creek, Lindis at Lindis Peak and Clutha Mata-au at Luggate did not meet the national bottom line for suspended fine sediment (visual clarity). The bacteria E. coli is measured to indicate safety for human contact. E. coli results did not meet the national bottom line at Upper Cardrona and Kawarau at Chards. Aquatic insect life did not meet the national bottom line at Mill Creek. Two of the three monitored lakes, Lake Hayes and Lake Johnson, did not meet the national bottom line for chlorophyll-a, a measure of algae levels in the water. A result consistent with the nutrient-enriched state of these lakes.

Despite most sites’ very good water quality, some degrading trends were identified. In particular, the Cardrona River had 10-year degrading trends for E. coli, nutrients (nitrogen and phosphorus) and an aquatic insect life metric. Luggate Creek had 10-year degrading trends for E. coli, nitrogen, and turbidity (poor visibility). Mill Creek had improving trends for nutrients and E. coli, but a degrading trend for turbidity.

Dunstan area Water Quality State and Trends Technical Report

Introduction to water quality

Dunstan Rohe water quality summary

Groundwater has been greatly affected by glacial advances and retreats. These cycles have created several large basins that hold relatively deep gravel aquifers and shallow alluvial ribbon aquifers near rivers and include the Hāwea Basin, Wānaka & Cardrona Basin, Whakatipu Basin, Cromwell Terrace Aquifer, Lower Tarras/Bendigo Aquifer, and the Lowburn Alluvial Aquifer. Groundwater use is high, with around 1,000 completed bores registered with the ORC.

Primary groundwater uses are domestic and stock water, irrigation, community supply, and monitoring. There are around 240 resource consents to draw groundwater in the Dunstan Rohe, with a total annual consented volume of about 89.874 million m3 a year.

ORC monitors groundwater quality in 16 State of the Environment (SoE) bores across the Dunstan Rohe. The results suggest good groundwater quality with low E. coli and nitrate concentrations below the Drinking Water Standards limits in most bores. However, a number of bores including some in Wānaka, the Wakatipu basin, and Lower Tarras, have had elevated E. coli, nitrate, and Dissolved Reactive Phosphorus (DRP) concentrations.

These are likely to reflect the rapid development of the area. Arsenic concentrations in most monitoring bores are generally below the limit, although elevated concentrations were measured in some bores. These are likely to be caused by the local schist geology. As schist is common across the rohe, groundwater users should regularly test their bore water.

The Dunstan Rohe includes rare and threatened ecosystems and species. Rare and vulnerable ecosystems associated with freshwater include ephemeral wetlands, inland saline ecosystems, lake margins, and wetlands.

These ecosystems contribute a lot to national biodiversity, however, are often threatened by processes such as land use change and invasive species. Little is often known about their extent and/or condition.

Many species depend on freshwater and ecosystems including fishes, invertebrates, plants, and birds. There have been 65 threatened freshwater-dependent species identified. The rohe provides habitat for native fishes including three non-migratory galaxias, four migratory galaxias (whitebait), two eel and five bullies. Some of these fish are threatened, for example, the lamprey and all non-migratory galaxias.

Freshwater invertebrates include koura, mussels, and threatened stoneflies. Threatened freshwater-dependent plants include Chenopodium detestans and Triglochin palustris. Many birds also depend on these ecosystems, temporarily or permanently, including the threatened Australasian crested grebe and black-fronted tern.

Some exotic fishes are found in the Dunstan Rohe, including goldfish, perch and four salmonids. Many native freshwater species are under threat and continue to decline in numbers.

Ten sites are recognised as Regionally Significant Wetlands. These are swamp (4 sites), fen (3), marsh (2), and bog (1).

On the delta where the Upper Clutha Mata-au runs into Lake Dunstan, the Bendigo Wetland (244 hectares) has developed swampy, willow-edged river margins. This wetland provides a habitat for diverse wildlife, and is especially valuable for birds and angling.

Further upstream, above Luggate, the Campbells Reserve Pond Margins (1 hectare) is a small marsh, spring-fed from seepage off the terraces above. Butterfield Wetland (2 hectares), on an old Hawea River terrace, is of similar origin, with a raupo-edged pond.

Two sites in the Nevis Valley, Nevis Red Tussock Fen (44 hectares) and Schoolhouse Flat Red Tussock Fen (9 hectares), have communities of red tussock and various carex species distributed according to the soil wetness.

At the head of the Nevis, in its Roaring Lion catchment, is New Zealand’s largest string bog system, which also extends into the Nokomai catchment, Southland. This system combines terraced tarns, fens, bogs, and snowbanks. In the Queenstown area, Lake Hayes Margins (17 hectares) has lake fringes of raupo, crack- and grey-willows, and some carex swamp.

Moke Creek Swamp (1 hectares) and Moke Lake Bog (12 hectares) have both bog and swamp types. In one of the heads of the Shotover, the Polnoon, the Church Hill Wetland Complex (103 hectares) occupies a fault-derived basin with glacial moraines, bogs, fens, tarns, and ephemeral wetlands.

Two additional sites are Queenstown Hill; a Conservation Covenant-protected site of cushion bog and tarn communities; and the head of Pisa Range Roaring Meg, with sedge and cushion bogs and tarns.