Two young women find fun during a flood in the Hatea River, Whangarei.
Northland has a dense network of rivers and streams. None of them are considered major on a national scale. Northland's narrow land mass means most of our rivers are relatively short with small catchments. Most of the major rivers have their outlets into harbours, with only a few discharging directly on to the coast. The Northern Wairoa River is Northland's largest river, draining a catchment area of 3650 square kilometres, or 29 percent of Northland's land area.
Rivers are channels for floodwaters, a function that is much needed with Northland's relatively high rainfall.
Rivers are ever changing because erosion is in progress all the time. Water action gradually breaks down rocks into smaller pieces and these are eventually carried downstream. The tiniest pieces become fine sediment which is washed out to sea - only for wave action in the ocean to deposit them back on land again as sand. The new material deposited protects the coastline from eroding through wave action.
While this type of erosion is a natural process, human activities can change that. Water needs to have natural channels to dispose of floodwater. If buildings are put on natural floodplains, there can be problems with flooding. Drainage and irrigation activities can change natural river characteristics.
Northland's unstable hill country means many of the region's roads have been built on flood plains. Flooding on roads creates problems for transport.
Rivers and streams are rich environments for native plants, fish and insects, and provide important sources of water for people, industry and irrigation. Any contamination of fresh water has wide ranging effects all the way through the ecosystem around the river. A healthy river needs a healthy stream feeding into it. Pollution and sediment will all have an effect. Action to clean up a small stream with have effects all the way downstream to the sea.
Rivers and streams are also enjoyed for their beauty and for recreation activities such as swimming, kayaking, fishing and rafting. They are important drawcards for tourists as well.
Northland Regional Council's role and policies
The Northland Regional Council (NRC) is responsible for the sustainable management of the region's natural and physical resources. It also supervises catchment and drainage activities.
The Council is guided in looking after the region's rivers and streams by the Resource Management Act and the Soil Conservation and River Controls Act.
The Wairua River, near Titoki, west of Whangarei.
We produce Plans for looking after the region's water resources. These Plans are required under the Resource Management Act 1991.
The Regional Policy Statement identifies issues relating to resource management in Northland - including water - and sets out ways of dealing with them.
The Regional Water and Soil Plan contains detailed policies and rules that the Council has decided are necessary for considering applications for Resource Consents. These include minimum water quality standards and minimum levels of rivers, lakes and groundwater to be maintained. The Council also has Catchment Management Plans, which help with the management of major catchments in the regions. These Plans include resource descriptions for each catchment, information on soil types, vegetation, land use, topography, stream or river types, water quality and rainfall data.
The Plans seek to define the area's flood plain and work out ways to reduce the risk to communities.
Management challenges include allowing progress in Northland without creating problems for the future. Flood plains need to be retained for their importance in a river's natural functions. Houses have been built on flood plains in areas such as Kaitaia, Whangape and Panguru, making hazard and risk assessment an important part of the Council's role. There needs to be a balance between reducing risk of flooding and affecting the flood plain and quality of habitats. Control of willow trees and water weeds is needed to allow floodwaters to drain quickly.
The NRC assists District Councils in producing flood management plans for urban areas and established drainage districts. Outside those areas the NRC is responsible for managing flood control and drainage. Flood Management Plans have been designed for Kaeo, Kaihu, Hokianga, Whirinaki, Pakanae, Panguru, Pawarenga and the Awanui. Others will be created in time for other flood-prone areas.
Northland rivers and streams
The types of rivers in Northland are influenced by the soil types they travel through on their journey to the ocean from high in the hills and ranges. The basin of land that drains into a river is called a water catchment. The size of the catchment is a factor in the size of the river that is created when all the water drains to the lowest point.
When rain comes, the large catchments and short rivers in Northland mean large volumes of water fill the valleys. Northland rivers tend to have a low normal flow but can rise very quickly with rain and cause flooding. However, flooding does not usually last long as the short rivers allow the water to quickly drain into the sea.
Major Northland Rivers
This map shows the main rivers in Northland and where they flow. Most of the rivers feed into harbours. Sometimes several rivers flow into one harbour.
Major catchments in Northland
Northern Wairoa River
The Northern Wairoa River is Northland's biggest river. It drains to the west coast.
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.
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 150 metres 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.
- Kaihu River: The Kaihu catchment, north of Dargaville, includes the western edge of the Tutamoe Ranges back to the Tutamoe settlement and the edge of the Waipoua Forest. It features a series of rocky gorges and waterfalls. Above Kaihu, 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.
- Mangakahia River: The Mangakahia River catchment covers about 800 square kilometres of central Northland, bounded by the Tutamoe 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.
The Mangakahia River has a big catchment and floods often.Awanui River
The Awanui River and its tributaries drain the northern side of the Mangamuka Range and flow northwards through Kaitaia 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.
Kaitaia 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 over the past 50 years has been done to lessen most flooding.
The Kerikeri River drains into Kerikeri Inlet from about 170 square kilometres of land. Streams in the catchment include Rangitane, Waipapa, Kerikeri and Puketotara which drain east. Two smaller catchments, Wairoa and Okura, drain northward.
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 Ngawha Geothermal Field near Kaikohe.
The catchment for the Kawakawa River covers about 820 square kilometres. Its northern boundary runs between Opua and Moerewa and its southern boundary is a low ridge separating it from the Hikurangi swamp catchment.
Waipu and Ruakaka rivers
The two main rivers feeding into Bream Bay drain a total area of 310 square kilometres. Most of the river flowing to the Waipu River drains 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 Waipu river.
What lives in the river?
There are 27 native freshwater fish species and several marine species that occasionally wander into Northland rivers.
Native fish include eels, mullet, flounder and lamprey. They have to compete with three major introduced species: rainbow and brown trout, and perch.
Rivers are important for most of our native freshwater fish, which have a time when they migrate to the sea. Whitebait is one example. Their young are washed out to sea after hatching and then migrate back into streams from the sea in springtime.
Adult eels migrate to their spawning grounds in the Pacific Ocean. Juvenile eels (elvers) return to our streams and rivers during summer.
It is important that their way is not blocked by manmade structures such as dams, weirs or culverts.
Some native freshwater fish can climb through these obstacles to make it back to their traditional habitats upstream. But some cannot make the journey and stay in lower parts of the rivers.
One native freshwater fish, the grayling, has already become extinct.
Consideration for the requirements of native freshwater fish is given in the design of any new structures. The Northland Regional Council requires the construction of a suitable "fish pass'' to enable the fish to travel along the waterway.
Types of native fish
Inanga is the most common of the whitebait family.
Whitebait is not a type of fish - it is the juvenile stage of several native fish.
Whitebait can grow into any of six different types of native fish:
- Inanga is the most common of the family. It spawns in river margin vegetation that is flooded by extreme high tides.
- Short-jawed kokopu is extremely rare although it can be found in Northland.
- Banded kokopu prefer stony, bush-covered streams but can survive in weedy farmland streams.
- Giant kokopu is a large fish that can grow up to 58cm in length.
- Kaoro prefer fast-flowing, stony habitats in upper catchments.
- Black mudfish lives in wetlands, not rivers. It can survive for long periods burrowed deep in mud when the water in their pool dries up. Early settlers often found them in their swampy potato patches - the original fish and chips!
Another family of native fish is the bully, which lives in freshwater and the sea.
Redfinned bully is the most common and colourful of native fish. It spawns in freshwater but the juveniles are washed out to sea.
Bluegilled bully prefers swift-flowing rivers and high quality water and is the smallest of the bully family.
Crans bully is common in upper parts of streams. It is capable of living its entire life cycle in fresh water. The headwaters where it is found may be up to 70km - 80km from the ocean.
Giant bully is the largest of the family.
Torrentfish thrives in fast-flowing turbulent water, but can also be found in slower, meandering rivers. They are not good climbers.
Smelt are found in lower reaches of streams and rivers. Sometimes called the cucumber fish because of the strong "cucumber" smell when they are taken out of the water. They are not strong swimmers so they struggle in strong currents and cannot pass waterfalls or dams.
Baby eels are called elvers.
There are two types of eels and both are found in Northland. They are both excellent climbers. They have an excellent sense of smell and feed mostly at night. Eels can live for up to 60 or 70 years.
Shortfinned eel prefers slower moving streams and lakes.
Longfinned eel likes the upper reaches of streams.
Lamprey juveniles are found in river gravel for several years until they reach a length of 80-100 millimetres. At this stage they undergo a metamorphosis, changing their colour from mud-brown to blue. Their eyes appear and the dorsal fin grows. In winter, the lamprey migrate to the sea where they attach themselves to a host fish with their sucker-like mouth and begin to feed on the body fluids of the host. Several years later they migrate back into streams for spawning.
Koura, native freshwater crayfish are widespread in Northland. New Zealand has two freshwater crayfish species, with this species being found throughout the North Island and in Northern and West Coast of the South Island. They are slightly smaller (up to 70 millimetres long in streams) and also less robust and hairy than their southern cousins. Lengths of crayfish are greatest in lakes (to around 160 millimteres), with ages over three years not being uncommon. They are largely nocturnal in their habitat of lakes, streams, and wetlands, where they feed opportunistically on aquatic insects and vegetation. Freshwater crayfish are thought to function as a keystone species, with the modifications they make upon the environment permitting a greater range of species to exist than if they were not present. These crustaceans also provide an important food source for larger fish and waterfowl. All koura are non-migratory, and carry their eggs and then their developing young under their tails. Juveniles are released as perfect miniatures of the adult, able to fend for themselves immediately.
Numbers of all native species have been reduced because of many factors, including loss of habitat, water quality and competition from introduced fish species. Many wetlands have been drained for farmland - such as the Hikurangi Swamp near Whangarei.
At the Wairua electric power station at Titoki, near Whangarei, Northpower has constructed a fish pass to allow eels and other native fish to climb the wall of the dam. This allows the fish to continue their natural migration upstream for breeding.
Some introduced fish eat whitebait - the young of native fish - so reduced numbers are surviving to become adults. They also compete for the same food as native fish. Others affect the habitat by burrowing into banks and affecting water quality.
The mosquito fish was introduced in the 1950s and 1970s to kill mosquito larvae - but unfortunately this fish is also a major competitor with native fish. The koi carp has been recently found in Northland. This fish has had a big impact in other parts of New Zealand because it undermines stopbanks by making burrows in the sides. Digging in the mud also affects water quality. The koi carp also competes with native fish for food.
Goldfish have ended up in many rivers in Northland, although they often don't keep the same gold colour once they breed in the wild. They can revert to olive or brown shades from their original colouring. Goldfish compete with native fish for food.
Importance to Māori
Rivers have spiritual significance to Māori as well as being a valuable food and water source for many marae.
To Māori, water is an essential ingredient, regarded as a taonga or treasure. It must be safeguarded for future generations.
Water is considered to possess a life force (mauri), and have a spirit (a wairua). To Māori, any discharge of contaminants into water, no matter how well purified in a treatment process, reduces the water's ability to sustain life. It thereby reduces its mauri, or life force.
Water is given different terms by Māori according to its status.
Waiora is water in its purest form, usually rainwater caught before it touches the earth. This water is used for ritual purposes.
Wai Māori is fresh water or drinking water from springs. It can be used for everyday purposes.
Waimate or Waikura is water that is stagnant or polluted, and is no longer capable of sustaining life.
An NRC monitoring station gathers data on water levels from the Wairua River near Titoki.
Northland Regional Council scientists and other staff constantly monitor our rivers and streams for such things as pollution, chemical runoff, water levels and flow rates. This is done in a variety of ways. Sometimes samples of plant and animal life are taken which show how healthy a river or stream is. Water quality tests can give clues to what the likely sources of pollution are and where contamination might have come from. Water levels and flow rates show if floods could affect landowners.
Water quality tests can include the following:
Dissolved Oxygen (DO)
A healthy stream needs cool water and lots of dissolved oxygen to support a wide variety of creatures. Low oxygen levels may suffocate and kill fish and the many other creatures that live in streams and rivers.
Biochemical Oxygen Demand (BOD)
When pollutants such as milk or raw sewage enter a stream, they break down very quickly. The decomposition process requires a lot of oxygen. This could mean all the oxygen might be removed from the water, killing all the creatures living in it.
Micro-organisms (bacteria and viruses)
Our staff test water for micro-organisms to ensure water is safe for swimming or shellfish collecting.
Some micro-organisms can cause diseases in humans and animals. High levels of faecal material can indicate the possible presence of these bugs.
Most creatures can survive in water temperatures ranging between 10 degrees Celsius and 25 degrees Celsius. If the temperature rises or falls outside that range, the creatures may die or move away.
Cool water contains the most dissolved oxygen, which is why trees planted along streams and rivers help keep streams healthy for fish and stream life.
Hot summer temperatures in Northland can heat the water to the point at which fish and other aquatic life have trouble breathing and may suffocate.
The pH test for water checks the acidic or alkaline measurement. Pure water is 7 on the pH scale. Any major change from discharges of acid or alkaline substances can harm water life. Lemon juice is 3 on the pH scale. Creatures prefer pH levels between 6.5 and 9.
When staff know of a specific problem in an area, they may conduct other tests to gather evidence and detect sources. For example, ammonia tests might be conducted along with faecal coliform tests if it is suspected that septic tanks are failing in an area. Ammonia is found in sewage less than 12 to 24 hours old. This test can help detect a recent sewage spill.
Flooding is common in many areas of Northland. Some roads have been built on flood plains. Above, water spills across the road during a flood near Whakapara.
Floods and droughts
A Whirinaki waterway completely dried up.
The high and frequent rainfall in Northland means flooding is common in many areas. In the winter particularly, Northland is prone to high intensity rains, and floods can be spectacular.
Sometimes intense rain can be experienced over small pockets of land, causing localised flooding. Floods can cause hillsides and roads to slip, power cuts, stock losses and lead to people having to evacuate if their houses are in danger.
Many parts of Northland average a serious drought every three years. Some stretches of river can almost dry up during a long summer drought. The Council keeps a check on river use so that water levels do not fall too low during droughts and affect the health of a river or stream. Farmers who have irrigation systems are required to stop taking water once the level reaches a certain low level. This ensures that aquatic life is protected as much as possible.
The monitoring team takes between 100 and 120 stream flow gaugings during the summer, and there are also automatic water quality instruments installed in some streams, which take continuous records. In response to a serious temporary water shortage in Northland, the Council can issue a Water Shortage Direction. This tells Resource Consent holders to reduce or stop taking water. Based on the current pattern of water use, the application of a Water Shortage Direction to large areas of Northland at any one time is unlikely. It is most likely that the need would be confined to a few sub-catchments at any one time. The maintenance of people's health is given the highest priority of water use when managing a crisis.
A water level measuring stick attached to the side of a bridge.Part of the Northland Regional Council's job is to warn people in Northland if there is danger from flooding. This helps people prepare for any danger, and allows farmers to move stock to higher ground.
The Northland Regional Council has set up 37 monitoring stations at different sites throughout Northland collecting information every 15 minutes. The Whangarei branch of NIWA operates another six water level recording sites.
The information gathered from these sites allows staff to offer an early warning system. Data on river levels is sent automatically to the NRC office, where staff can monitor any danger from flooding.
The water monitoring system records changes in water levels and transmits these measurements to the computer system in the Whangarei office. The data is stored by the computer, giving staff access to round-the-clock records at any time.
The Council also has access to river level and river flow information from the National Institute of Water and Atmospheric Research, NIWA.
The Council keeps track of heavy rain warnings issued by weather forecasters, and warnings are issued on the Council's website and by sending notices to local media.
During an emergency, the Northland Regional Council's Emergency Management Plan - together with the various district councils' operational plans - provides the framework to co-ordinate organisations, services and people to guard against the effects of a disaster.
All the emergency services work together to help communities during a crisis. Find out more about civil defence and emergency management in Northland.
The demand for water is growing as Northlanders operate their homes and businesses, and more people move into the area. Anyone wishing to take water for any purpose other than household supply or stock watering purposes must have a Resource Consent from the Council.
This allows us to keep track of the demand on our water supply and make sure it is managed properly so it is sustainable.
A Resource Consent is required before anyone can:
- discharge waste into water;
- dam or divert a stream;
- divert or discharge floodwaters;
- build a bridge over a waterway;
- take water other than for domestic use, and depending on the location of the take, for stock requirements; or
- take from groundwater.
Any of these activities can have an effect on the water supply for other people, so the Resource Consent usually has rules to control the way an activity is carried out. Some Resource Consents require regular monitoring. Often the consent holders choose to carry out monitoring themselves. This information is then checked regularly by our staff.
Consents might also specify how much water can be taken, and minimum river levels, so that the consent holder cannot take water during severe droughts.
Agriculture is the greatest user of water in Northland, consuming nearly half of the allocated surface water total. This water is mainly used for irrigation, and to a lesser extent for washing down cowsheds and for stock water. The largest amount of water taken from above ground in Northland is by the Mangakahia Irrigation Committee, with a consent to take a combined total volume of 19,400 cubic metres per day. This water is taken from the Mangakahia River west of Whangarei.
Horticulture uses 33 percent, or 188,524 cubic metres per day, of the total volume of water allocated in Resource Consents. Most of the horticultural activities take place on the fertile volcanic soils near Kerikeri, Piano Hill (north Whangarei), Maungatapere and Maungakaramea and on the sandy clay loam soils on the west coast near Dargaville.
Water supply to towns and cities accounts for 19 percent of the total allocation of water for Northland. This figure will increase as populations in towns and cities grow and industry uses more water supplied from district council sources. The district councils are the main suppliers of water, taking from streams, rivers and dams. As coastal development takes place, demand for water supply in these areas will increase and the ability to meet these needs will be more difficult. These areas are prone to lower rainfall and longer periods of dry weather.
What can you do?
The biggest threat to rivers and the wildlife that lives in them is the development of land for farming. Large sections of wetlands have been drained to make paddocks and large stretches of waterways have been exposed to the heat of the sun since riverside vegetation has been cleared. Direct access to rivers and streams for stock has led to the trampling and eroding of riverbanks and contamination of water with their waste.
Actions you can take include:
- spreading the word about native freshwater fish;
- helping people understand the importance of habitats;
- promoting the need to maintain wetlands;
- promoting the importance of riverside planting;
- lobbying for the maintenance of unpolluted waterways;
- joining a streamside care group;
- keeping an eye out for problems on rivers such as logjams, erosion or flooding and alert the Council;
- looking out for weeds that can cause problems include willows, privet, yellow ginger, walnut. Property owners can help by walking along riverbanks and pulling out these plants before they become a problem;
- checking riverbanks for erosion after floods, and monitoring the changes; and
- letting the Council know if you see cars dumped in waterways as they can be a pollution problem.
Our staff cannot be everywhere at once to keep an eye on Northland rivers and streams. They rely on people to help by reporting any pollution or problems. We have offices in Whangarei, Kaitaia, Opua and Dargaville.
The Council operates an Environmental Hotline 24 hours a day, seven days a week. It is toll-free. This number should only be used for emergencies such as pollution spills.
The number for the environmental hotline is:
0800 504 639
Sources: Northland Regional Council staff; Water, Northland's Precious Resource, NRC booklet; Rivers and Us resource unit, NRC booklet; Schools in the Environment, winter 2000, No. 14; Keith Hawkins of Department of Conservation.