Facts about water
Groundwater
What is groundwater?
Groundwater is rainwater that has travelled through the soil to underground aquifers - areas of fractured rock or porous sediments such as sand or gravel.
Wells pump groundwater from aquifers. We use it for drinking and in agriculture, horticulture and industry.
Groundwater in Northland
Groundwater in Northland is highly changeable in both quantity and quality - depending on the geology of the aquifer system.
Our main aquifer systems exist in the:
- Kaikohe basalts;
- Whāngārei basalts; and
- Aupōuri sands
There are also many small sand and gravel coastal aquifers in Russell, Matapōuri and Taipā, and less productive greywacke aquifers throughout the region. Rainfall is the main source of replenishment for our aquifers.
Groundwater tends to refill during winter due to heavier and more consistent rainfall. Less rain in summer has little impact on groundwater levels, but a dry winter can be a problem. What mainly affects late summer groundwater levels is the length of time since the last significant rainfall.
On sand country, rainfall filters quickly into the ground. This refills the groundwater rather than contributing to stream flows. For example, many streams on the Aupōuri Peninsula have little or no base flow. In sand aquifers along the coast, salt-water can leak into the groundwater when there is over-use or the resource is low.
Our region’s changeable geology has a major influence on flow systems. Some types of rock allow water to pass through more easily than others. In Northland, the fractured basalt rocks absorb rainfall easily and water is slowly released through springs. This slow-release sustains the flow during dry periods.
Catchments that don’t absorb water easily soak up less rain. This leads to less water available in storage. Flows from these catchments tend to dry up more quickly during dry summers.
The main aquifers we study and monitor are generally either basalts, quaternary sands and gravels, volcanic deposits, geothermal or greywacke.
Rivers and streams
Northland has a dense network of rivers and streams. Because of our narrow land mass, most of our rivers are relatively short with small catchments. None of them is considered major on a national scale.
Rivers are channels for floodwaters, a function that is much needed because of Northland's relatively high rainfall.
Our rivers and streams provide habitat for a range of indigenous flora and fauna, as well as being an important water supply for rural communities, horticulture and agricultural demands.
As the majority of Northland’s rivers flow into harbours rather than open coastline, poor river water quality can also affect the health of our harbours.
The Northern Wairoa River is our region’s largest river, draining a catchment area of 3650 square kilometres, or 29 per cent of Northland's land area.
Major catchments in Northland
Northern Wairoa River
The largest Northland river is the Northern Wairoa near Dargaville. It drains a catchment area of 3650 square kilometres. The Northern Wairoa occupies a drowned river valley system and is tidal for about 100km inland.
Rivers that contribute to the Northern Wairoa river are:
- Manganui River:
The Manganui River drains a 90 square kilometre catchment of low rolling hill country, most of which is less than 150m above sea level, except for the northern boundary of the catchment which is formed by the Tangihua Ranges. The Manganui is slow-flowing and meanders through swampy valleys subject to frequent flooding.
- Kaihū River:
The Kaihū catchment, north of Dargaville, includes the western edge of the Tutāmoe Ranges, back to the Tutāmoe settlement, and the edge of the Waipoua Forest. It features a series of rocky gorges and waterfalls. Above Kaihū, the river flows over boulders.
- Awakino River:
This river drains a catchment area of 116 square kilometres, including the western and southern slopes of Tutamoe.
- Tangowahine River:
The Tangowahine has a catchment of 125 square kilometres. It flows through a gorge at the northern end of the Mangaru Range and then opens out into a broad, easy valley.
- Kirikopuni River:
The smallest river in the Northern Wairoa catchment is the Kirikopuni, which drains a narrow valley between the Mangaru Range and the Mangatipa and Houto. The Kirikopuni frequently floods the whole valley floor.
- Mangakāhia River:
The Mangākahia River catchment covers about 800 square kilometres of central Northland, bounded by the Tutāmoe Range in the west and the Wairua River catchment in the east. It has the largest and most rapid flood discharge of any in the Northern Wairoa system.
- Wairua River:
The Wairua River drains the north-eastern corner of the Northern Wairoa Catchment via the Hikurangi Swamp. The large swamp was drained and turned into farmland in the 1970s. Once a lake bed, the swamp is susceptible to heavy rain storms from the north-east and a restricted outlet, making flooding common. The catchment covers 750 square kilometres.
Awanui River
The Awanui River and its tributaries drain the northern side of the Mangamuka Range and flow northwards through Kaitāia and across the Awanui flats to enter the Rangaunu Harbour at Unahi.
The tributaries, Te Puhi stream, Victoria River and Takahue River, are all fast flowing mountain streams with gravel river beds in their upper reaches.
Kaitāia sits on the floodplain at the point where the river is confined, before spilling out on to an alluvial fan and the Awanui flats. Extensive drainage and flood control has been done, over the past 50 years, to lessen most flooding.
Kerikeri River
The Kerikeri River drains into the Kerikeri Inlet from about 170 square kilometres of land. Streams in the catchment include Rangitāne, Waipapa, Kerikeri and Puketōtara, all of which drain east. Two smaller catchments, Wairoa and Ōkura, drain northward.
Waitangi River
With a catchment of 308 square kilometres, the Waitangi River draws water from most of the land between Kaikohe, south of Kerikeri and north of Moerewa. The Waitangi River flows into the Bay of Islands at Waitangi. A tributary, the Waiaruhe River, drains the Ngāwhā Geothermal Field near Kaikohe.
Kawakawa River
The catchment for the Kawakawa River covers about 820 square kilometres. Its northern boundary runs between Ōpua and Moerewa and its southern boundary is a low ridge separating it from the Hikurangi swamp catchment.
Waipū and Ruakaka rivers
The two main rivers feeding into Bream Bay drain a total area of 310 square kilometres. Most of the rivers flowing to the Waipū River drain from the Brynderwyn Ranges, in the south, through the Ahouroa, Waionehu and Waihoihoi Rivers. The Ruakaka river flows in an easterly direction, draining an area half that of the Waipū river.
Lakes
A number of dune lakes are grouped on the Aupōuri, Karikari and Poutō Peninsulas. Lake Taharoa, of the Kai Iwi group, is one of the largest and deepest dune lakes in the country, covering an area of 237 hectares and 37 metres deep.
Northland has a large number of small, shallow lakes. Most of these have been formed between stabilised sand dunes along the West Coast. The dune lakes are grouped on the Aupōuri, Karikari and Pouto Peninsulas. They vary in size, with the majority being between five and 35 hectares in area, and generally less than 15 metres deep. Lake Taharoa of the Kai Iwi Group is one of the largest and deepest dune lakes in the country, covering an area of 237 hectares and being 37 metres deep.
Water quality in Northland's lakes ranges from almost pristine to heavily impacted. Impacted lakes suffer from the effects of surrounding land use and introduced invasive weeds and fish.
Wetlands
What is a wetland?
The term ‘wetland’ covers habitats in which the land is covered or saturated by water for most of the time.
Why wetlands are important
In the past, many people have not recognised the true value of wetlands. This led to most of them being destroyed and turned into pasture. Wetlands play an important hydrological and water-quality role. They also provide a home for a number of unique plants and animals.
A giant sponge
Wetlands act as a giant sponge by helping to control water flow and quality. Plants in wetlands slow the flow of water off the land. This helps during flooding when more water can be absorbed into the soil and used by the plants. In summer, stored water is slowly released from wetlands, maintaining water flows.
Cleansing the system
Bacteria in wetlands’ damp soils contribute to cleaner water by absorbing and breaking down about 90 percent of the nitrogen contained in farm run-off (such as in fertilisers, chemicals and animal wastes). This cleaner water prevents nuisance algal blooms and is better for livestock and wildlife. Plants also trap waterborne sediment, preventing silt entering streams and harbours.
A food source
Wetlands are among the most productive places on Earth, providing an enormous food source for fish, birds and other animals. They absorb large amounts of water and nutrients from outside sources and contain micro-organisms (fungi and bacteria) that efficiently decompose and recycle nutrients.
A cultural treasure
Wetlands are also important to Māori, featuring in the history and culture of many hapū. Wetland plants provide traditional materials for clothing, mats, medicine and dyes. Wetland animals, especially tuna (eels) are valuable food sources.
Wetland types in Northland
In Northland, we have six main types of wetlands:
- bogs
- coastal wetlands
- swamps
- lakes and ponds
- dune lakes
- rivers and streams.
Bogs
Bogs are very rare and precious in the Northland region. Fed only by rainfall, they are low in fertility and acidic. They are home to a variety of specialist plant life, with the wettest dominated by sphagnum moss. In Northland, bogs are home to the nationally threatened mudfish species. Drier bogs support a variety of plants including sedges, rushes, umbrella ferns and manuka.
Coastal wetlands
Estuaries (including salt marshes) are the most productive of all wetlands, and especially rich in animal life. Many coastal fisheries depend on estuaries as fish spawning grounds.
Swamps
Most wetlands on private land are swamps. They are more fertile than bogs because the water flowing through them brings silt and organic matter. Swamp water levels fluctuate seasonally.
Typical swamp plants include raupo, purei and harakeke (flax). The organic matter these plants produce encourages large populations of aquatic invertebrates including insects, water-snails, crustaceans, worms and birds, such as the nationally threatened spotless crake and matuku (Australasian bittern).
Lakes and ponds
Lakes are permanent areas of fresh water. Open water areas with shallow margins surrounded by swamp vegetation provide important water bird habitat, including the endangered pateke (brown teal), which is now restricted to two small populations on the east coast of Northland and on Great Barrier Island.
Dune lakes
Northland is home to a large number of dune lakes. These lakes within sand dune systems are often highly dynamic, with fluctuating water levels, shorelines and shapes that are continually being changed by shifting sand dunes or, where stabilised, by reductions in water tables. Dune lakes are home to a large diversity of native plants and animals, including the rare freshwater fish, the dwarf
inanga, which are only found in some dune lakes in Northland.
Unique wetland wildlife
Wetlands support an immense variety of animals, some of which are very rare.
Most of New Zealand’s wetland animals are not found anywhere else in the world. They include fernbirds, New Zealand dabchicks, New Zealand scaup and paradise shelducks. Mudfish are also unique.
Animals that can only live in wetlands face an uncertain future through habitat loss and/or damage. Many, like the Australasian bittern, pateke and short-jawed kōkopu, are now endangered. Conservation and restoration programmes help to provide the habitat they need and ensure our wildlife survives into the future.
Did you know?
Wetlands now cover less than 2 per cent of New Zealand’s land area, but are home to 22 per cent of our native land bird species.