Motueka/Riuwaka FMU

Note: text in italics shows the sections of the vision specific to this FMU.

It is 2100, our waterbodies are healthy, connected and resilient where indigenous ecosystems and biodiversity are thriving, providing abundant mahinga kai, food and resource gathering and fishing. All waterbodies and their margins have high natural character and have room to move and adapt.

It is 2035, our land and freshwater management provides for our community’s social, economic and cultural wellbeing. People have access to safe, clean water for drinking, swimming, recreation and cultural uses.

It is 2040, sustainable and integrated land and water management practices protect the ecosystem health and natural character of our aquifers, rivers and their braids, lakes, springs, tomo, karst sinkholes, and wetlands, and provides for our agriculture, tourism, commercial and industry sectors. 

It is 2055, our communities and livelihoods are resilient to our changing climate, floods and droughts. We have enabled use of renewable energy and water storage and our food producing areas continue to play an important role for local food security.

We all respect and take responsibility for freshwater health. We value the taonga we are protecting. Through collaboration and innovation we have adapted to new ways of doing things. We have restored, protected and maintained freshwater habitats and the quality and quantity of freshwater, enabling sustainable use for generations to come.

Rivers and streams that flow through the heart of our landscapes have high water clarity and have margins of healthy indigenous vegetation. Wetlands have been restored in our river deltas.

Parts of the Motueka and its tributaries are outstanding water bodies with protected recreational, fisheries and wildlife habitat, scientific and wild and scenic values. The Riuwaka Resurgence is protected as a treasured site.

Note: Values in italics are relevant to the Water Conservation Order for this river.

These are the key freshwater challenges for the Motueka FMU:

• Fine sediment discharges to rivers and then to estuaries and coast.
• Rehabilitation of historical river and stream modification and returning streams to a more natural, more ecologically healthy state.
• Groundwater bore security for safe drinking water.
• Water availability in some areas.
• Ensuring the natural state of important rivers continues to be protected.
• Nitrate concentrations in smaller streams such as Woodlands and Thorpe.

The Motueka FMU has a generally warm and mild climate. Mean annual sunshine hours (2,407) are among the highest in New Zealand. Frosts can occur between April and October and snow can fall during all months at higher elevations.

Rainfall is strongly seasonal and varies significantly with topography. The mountainous northern areas of the FMU are characterised by relatively high rainfall, of about 3,500 mm / year. The southern areas including the settlements of Motueka, Brooklyn, and Riuwaka, by contrast are relatively dry, with rainfall of around 1,000 mm / year.

The Motueka Catchment is geologically very complex compared to many other South Island catchments.

Ultramafic and old sedimentary rocks form the mountains at the south-western end of the Richmond Range in the headwaters of the Motueka. The ultramafic rock has high Iron, Chromium and Nickel levels. In this special mineral belt, where the soil repels most native trees, a unique shrubland community has evolved. 

The complexity of landforms, climate and sedimentary and igneous rock types such as marble, limestone, greywacke, argillite, diorites, gabbros, granite, mudstone and sandstone have resulted in a wide variety of soils including deeply weathered and highly erodible Separation Point Granite.

The hilly terrain of the Moutere Depression makes up most of the eastern side of the catchment. It is underlain by much younger alluvial sediments of the Moutere gravels. This is a thick (0.7 km near Tapawera), deeply weathered gravel, dominated by greywacke sandstone fragments, within silt and clay.

The complexity of landforms, climate, and rock types in the Motueka Catchment results in a wide variety of soils. Land alongside the rivers and a large area near the coast including the township of Motueka comprise very versatile, high quality soil formed on alluvium. Soils of the upper catchment are often prone to erosion when cleared or disturbed, and are of low fertility.

Rivers and streams

The Motueka River has a large, predominantly mountainous and hilly catchment of 2,076 km². The river originates at an altitude of 1,800 metres and flows for 110 kilometres along a narrow valley below Tapawera to follow the foot of the Western Nelson Range (Arthur Range/Wharepapa) towards Tasman Bay/Te Tai-o-Aorere. It has a mean flow of 58,560 litres/second (l/s), a median flow of 33,950 l/s, and a mean annual low flow of 10,216 l/s at Woodstock. The river is prone to high flows and some large floods and extended periods of low flow during summer.

The Motueka River is braided in the approximately 10km reach below the gorge, through Kohatu and to the Wangapeka River However, its natural path has been narrowed and straightened in its lower reaches, with stopbanks installed on the Lower Motueka River up as far as Peach Island, primarily to protect the Motueka township and surrounding infrastructure from flooding.

The western tributaries of the Motueka River, notably the Wangapeka and Baton Rivers, originate in the Arthur and Owen Range and have higher flows similar to the rivers in the higher rainfall Golden Bay area. They contrast greatly with the small rivers such as the Dove and Stanley Brook rivers originating in the Moutere Hills, as parts of these can dry up completely in summer.

The Riuwaka River has a 105 km² catchment that flows into Tasman Bay three kilometres north of the Motueka River, and also includes a number of tributaries. For part of its journey, the river flows underground through limestone caves, returning to the open air at Te Puna ō Riuwaka / The Riuwaka Resurgence.

Wetlands and lakes

The Waiwhero wetland is a large (16ha), natural wetland in the FMU. There are other small but ecologically significant areas of wetland found at the coast and scattered throughout the catchment. Several artificial wetlands have recently been and are being created beside the Motueka river in areas where river gravels have been extracted. Only 2% of the original wetlands of the Motueka-Riuwaka coastal outwash plains remain.

Groundwater

Groundwater in the Motueka Plains groundwater system is contained within alluvial gravels (known as the Motueka Gravel Aquifer) forming the coastal delta of the Motueka and Riuwaka rivers. The Motueka gravels are thinnest (approximately 6m) at the inland margins of the plains, and thicken to 30 metres in the central plains area, where they are the cleanest and most permeable. 

The catchment to its west includes the nationally recognised Mt Arthur karst cave system. A high-yielding aquifer comprised of three interlinked layers underlies the central part of the Motueka Plains.

The aquifer system is highly interconnected with the Motueka and Riuwaka rivers. A large proportion of aquifer recharge is sourced from these rivers. Additional water is supplied by rainfall and irrigation recharge across the plains. Groundwater exits the aquifer system by subsurface flow into Tasman Bay, into springs near the coast, into rivers, or via groundwater pumping.

Coastal receiving environments

The Motueka – Riuwaka Delta, is made up of four estuaries which are described in more detail on this page.

Tall forests are believed to have originally dominated much of the FMU, with podocarp species in the fertile lowland areas and varying beech species elsewhere. A band of coastal scrub is likely to have occurred along the coastal margin, and alpine tussock grasslands would have covered the catchment above an elevation of about 1200–1400 metres.

The Motueka River was once free to meander and braid, to alter course and flood widely across the plains. Such a dynamic environment would have produced a mosaic of forest, scrub, shrublands, gravelfields, braids and wetlands, with gradients between them, and successionary phases of renewed forest growth within the immediate riparian environs.

The Motueka Plains were cleared of forest by Māori initially, other than for Te Maatu, ‘the Great Wood’ of some 350 ha or so of podocarp-rich forest that ran south-west in a band from what is now Motueka township to the Motueka River. Most of the subsequent forest clearance occurred in the mid-to-late 1800s with European settlement.

The main land uses in the Motueka Catchment today are:

• native forest (35%) - the largest areas found in the headwaters of the western tributaries (Kahurangi National Park) and in the upper catchment (Mt Richmond Forest Park). These areas are very important for soil and water conservation and biodiversity.
• exotic forest (25%) - occupies large areas of the steeper and less fertile soils on both Moutere gravel and Separation Point granite.
• pastoral grassland (19%) – generally sheep and beef farming, but increasing dairying,  occupies the lower and easier slopes of the Moutere Depression, the west-bank tributaries, and the river flats and terraces.
• scrub (12%) - dominated by fern, gorse and manuka, occurs throughout the catchment, mainly on the poorer soils on steep hill country. Scrub reversion is a major challenge for pastoral farming in many parts of the catchment.
• tussock grasslands (7%) is located in the subalpine areas.

Horticulture (pipfruit, berryfruit, hops, vegetables) occupies a small, but expanding, area on the river flats and terraces and is a major water user. Most crops are irrigated from surface or groundwater during the summer.

Motueka is the significant urban centre in the FMU with a population of around 8,000. There are smaller settlements at Riuwaka, Brooklyn, Ngatimoti, Dovedale, Tadmor and Tapawera.

Freshwater Ecosystems

The Motueka FMU has a moderately diverse range of native freshwater fish species. It contains 20 of New Zealand’s 51 native fish species, including galaxiids, bullies, and eels. There are also five estuarine and marine fish species in the lower reaches, essentially black flounder, kahawai, yellow-eyed mullet, stargazers and cockabully.

Of the native fish species in Tasman, more than half (currently 12) are listed as At Risk or Nationally Vulnerable by the Department of Conservation. This high proportion of species with declining populations is largely due to broad-scale land use changes which has led to the degradation of fish habitat in waterways.   

• Common bullies are found in coastal streams and waterways. Common smelt are found on the Motueka River.
• The threatened and declining Torrentfish is found on the Motueka and Riwaka Rivers. Dwarf galaxias and brown trout seem to coexist in reasonable numbers in tributaries of catchments such as the Motupiko.
• Despite the catchments in the upper Motupiko River and Roundell Creek having large areas of original sub-alpine bog/wetlands leading to highly stable, moss-covered streambeds, the fish community has low diversity and relatively low numbers of fish, apart from brown trout.
• A bluebill bully was spotted in the Riwaka catchment in 2011.  However, numbers of fish in this waterway are surprisingly low and the reasons for this are unclear, despite invertebrate numbers being good.
• The lower reaches of the Brooklyn Stream, have been found to contain nine different freshwater fish species through various surveys recorded since 1996. Consequently, this stream has one of the highest fish diversity of any stream in the district.
• Reasonable numbers of mature redfin bullies have been found on the Humphrey stream, a species that is usually not common in the Motueka catchment.
• Upland bullies are found on the Wangapeka River.
• Lamprey are found on 6 sites in the Motueka catchment including Brooklyn, Lower Dove, Lower Tadmor and Lower Motupiko.
• Northern flathead galaxias is an undescribed species found in the upper Motueka River. 

Macroinvertebrate communities are diverse (at least 119 taxa dominated by caddisflies, true flies, mayflies, and stoneflies) and generally dominated by species characteristic of unpolluted habitats, unmodified streams, and high aquatic habitat quality.

There is a Water Conservation Order over the Upper and Middle Motueka River, based on nationally significant trout fishery and high natural and intrinsic values. The Motueka and Riuwaka rivers contain important trout fisheries. 

The Motueka River is used by river-nesting birds such as Oystercatchers, Black-billed gulls, Banded Dotterels and Pied stilts. This reach is used for nesting by Black-fronted terns, Banded dotterel, and South Island Pied Oyster-catcher. The threatened blue duck has been reported from the Pearse, Baton, Wangapeka and upper Motueka rivers.

The only natural lakes in this FMU are very small and alpine/sub-alpine within the conservation estate e.g. Luna Lake in the upper Wangapeka catchment.

Forest habitat

The distribution and abundance of native fauna have been severely affected by the removal of much of the forest from lowland areas of the Motueka Catchment. There are still large upland areas of native forest with a wide variety of birds and other animals, but few examples of large tracts of lowland forest or unmodified freshwater and coastal wetlands.

The area of the west-bank tributaries around the Arthur mountains retains more of its original vegetation, bird and animal life than other areas. Formerly the area would have been almost entirely covered in forest. The alluvial plains and terraces supported towering podocarp forests and pockets of broad-leaved forests in sheltered lowland sites. While the low hills contained mixed forest of black beech, hard beech, rimu, totara, kāmahi, tītoki and tawa.  Along the coastal bluffs and fringing the estuaries, ngaio, cabbage tree, kōwhai and totara would have been common.

Black beech and kahikatea are dying out across the FMU. Silver beech, rimu, pokaka, kowhai, tarata, manatu and narrow-leaved lacebark are all scarce or rare.

Forest sites contain a wide variety of birds (including kākā, yellow-crowned parakeet, falcon, kiwi, blue duck, fernbird, robin, rock wren, kea, long-tailed cuckoo) and are also notable for large land snails (Powelliphanta).

Estuarine and saltmarsh habitat

Historically, estuarine ecosystems that are the receiving environment for the Motueka FMU freshwater system provided habitat for a diverse range of birds, reptiles and invertebrate fauna in densities and diversities unimaginable today.

However, all four estuaries (Ferrer Creek Estuary, Motueka River Estuary, Motueka Estuary and the Riuwaka Estuary) have suffered from extensive historical habitat modification, in particular the removal of salt marsh, reclamation of estuary areas, and the interruption of natural flow regimes. This has significantly reduced habitat diversity, and is continuing to do so. Despite these past changes, all four estuaries retain significant ecological value and the Department of Conservation regards the Motueka delta as being of national importance.  The estuarine and coastal area around the mouth of the river is important for a range of fish and shellfish, while Tasman Bay supports a wide variety of plankton, benthic organisms and fish. The Motueka Sandspit is formed with sand and gravels of the Motueka River and is internationally important habitat for kuaka/Eastern Bar-tailed Godwits, torea-pango/Variable Oystercatchers, torea/South Island Pied Oystercatchers and Banded Dotterels and nationally important for Ruddy Turnstone.  Scallops, oysters, mussels, cockles and snapper are important commercial and recreational fisheries.

Salt marsh is relatively extensive in the estuarine area from the Riuwaka River to Motueka and made up 69ha (28.2% of the intertidal area). An estimated 60-75% of the historical salt marsh cover was lost prior to 1947 due to drainage, reclamation and land clearance.  The muddiest estuaries were Ferrer Creek and Riuwaka, whose extent of mud-dominated sediment (24% and 18%, respectively) was high in both a regional and national context. Motueka River and Motueka Estuary had very little mud (<2%). Nuisance macroalgae was scarce. Seagrass is present from the Riuwaka estuary towards Tapu Bay. 

Rivers and streams

The current state of water quality at the river sites in the Motueka FMU has been evaluated using the National Objectives Framework of the National Policy Statement – Freshwater Management. Under this framework, key attributes to assess water quality are Total Ammonia, Nitrate-N, Dissolved Reactive Phosphorous, Water Clarity,  E.coli, and Macroinvertebrate Community Index (MCI). Each water quality attribute is ranked from A through D (or A through E for the E.coli attribute) with the D (or E) band representing poor water quality at each river site. Trends over 5 and 15 years are also assigned based on five classes from very likely improving to very likely degrading.   

Water quality is generally good across the FMU. For example:

• Water clarity in the upper Motueka and Riwaka Rivers is very high by New Zealand standards. The Wangapeka River is not far behind. The waterways that arise from karst springs (resurgences) of the west bank mid Motueka, such as the Pearse and Graham Rivers, also have very high water clarity.
• Nutrient concentrations are relatively low compared to other parts of New Zealand
• Dissolved Reactive Phosphorus is likely improving at a number of sites on the Motueka, Wangapeka, and Riuwaka Rivers.

However, there are some streams and rivers, and results that are cause for concern, including:

• A reasonable proportion of small, low-gradient unshaded streams have poor water quality. In summer, water temperature is high (often >21oC and over 24oC for some), dissolved oxygen is low​ and there is poor macro-invertebrate condition, often with high suspended sediment concentrations. This is particularly the case with streams draining pasture and horticultural land.
• Fine sediment discharges are a problem in the FMU particularly during flood events. It amplifies the effects of other contaminants such as disease-causing organisms and nutrient issues, as these contaminants bind to the sediment and then prevail in the stream bed for much longer.
• Nitrate concentrations are rising in the Motueka River although they are still at reasonably low levels (Band A). This is the case at Woodstock, and the Gorge site even though 98% of the land area of the catchment upstream is in a natural state. However, total oxidized nitrogen is rising six times faster at the Woodstock site and appears to be degrading faster in the last 5-10 years. Filamentous green algae growth is already an issue at times in this river and is likely to get worse if this trend continues. Nitrate concentrations are highest in the Woodlands and Thorpe Creeks in Motueka (based on only a few samples).
• The macro-invertebrate index (MCI) is in the C band on the Motueka River at Woodstock and is ‘very likely degrading’. The same pattern is occurring at the Gorge, so this could be partly related to natural causes such as the runoff of heavy metals from dissolution from the ultramafic geology in the headwaters. Interestingly the MCI is also ‘very likely degrading’ in Hunters Creek which is in native bush. This could be due to sediment discharges from pig rooting that is prevalent in this catchment.
• E.coli concentrations and Total Ammonia are degrading on the Motueka River including at the Gorge, the SH60 Bridge and at Woodstock. Each of these sites in in the A Band except for E.coli concentrations which are in the Band B at Woodstock.
• E.coli concentrations are below national bottom lines on the Sherry River (Band D) but are likely improving. E.coli concentrations have dramatically improved since the early 2000’s when cows were progressively removed from the waterway and then more latterly when a dairy farm was converted to hops. However, nitrate levels are now increasing, likely as a result of fertiliser application from horticultural use.   
• In relation to the Riuwaka River, despite E.coli concentrations being in the B band, they are ‘very likely degrading’ with an unknown cause. While MCI is in the B Band, it is ‘likely degrading’ over the last 10 years (‘very likely degrading’ over the last 15 years).
• The Motueka River at Alexander Bridge and SH60 are typically swimmable over 80% of the time.

Stream Habitat and function

• The lower Brooklyn Stream, Ferrer and Little Sydney Streams (between the Motueka and Riuwaka Rivers), as well as Thorpe and Woodlands Streams in Motueka township have been straightened, have narrow corridors and have little or no riparian native tree cover leading to lack of diverse ecological habitats. As a consequence, there is relatively low fish and invertebrate species diversity and abundance, despite the good water quality.
• Fish passage is likely to be compromised at tidegates on the Little Sydney, Ferrer, Lodder, Kumara, Moon, Doctor, and other creeks.  

Groundwater quality

Overall, the groundwater quality in the Motueka/Riwaka Plains is good with no significant changes to the majority of water chemistry parameters over time. The majority of the parameters tested for were well within the Drinking Water Standards for New Zealand (DWSNZ) for both the health significant and aesthetic factors. This includes:

• Nitrate concentrations are reasonably low despite the widespread agricultural and horticultural activities on the plains.
• Where pesticide residues were detected they were well below the maximum acceptable values in the DWSNZ.
• None of the selected bores in the Tasman region had glyphosate detected.
• Only 2% of samples were positive for E.coli and 18% contained total coliforms (an early warning to know if water quality is changing).
• Two bores in the Motueka / Riwaka Plains had detections (at very low levels) of emerging organic contaminants (EOC).

However, the aquifer underlying the Motueka / Riuwaka Plains that water is sourced from is unconfined/semiconfined (leaky). Because of this it does not meet the Drinking Water Standards New Zealand (DWSNZ) definition for secure groundwater. This means that despite the good quality of the groundwater currently, there are health risks because of the potential for contamination.

In addition to this, because many bores are old, they are often not sealed at ground level they have risk from the local surrounding e.g. rubbish and chemicals stored nearby. Some are located in low-lying areas or near stormwater drains, increasing risk of localised runoff contamination.​

Receiving environment water quality

Coastal water is likely to be in generally good health given the amount of dilution from clean seawater and relatively good water quality in the larger rivers. However, the detectable sediment plume from the Motueka River covers an area of sea bed of about 180km² with plume-affected nickel concentrations up to six times higher than guidelines. Additionally, areas around Port Riuwaka are not considered swimmable for over 20% of the time. This may be due to discharges from live-aboard boats or cross-connections at dwellings.

Water demand and uses

The aquifer system underlying the Motueka-Riwaka Plains is a primary source of water for irrigation, industrial, community, domestic and stockwater supplies in the FMU. Irrigation is the largest water user.

Both the Motueka township and the nearby Riwaka settlement provide reticulated community water supplies from the aquifer system with one-third of the houses in Motueka connected to the Tasman District Council water supply. Council have recently opened a water treatment plant that now provides good quality chlorinated water to reticulated users.

There is an estimated 2,000 private (shallow) domestic bore water takes in Motueka, used for both domestic and commercial/irrigational purposes. This makes Motueka the largest town in New Zealand that doesn’t have a fully reticulated (networked) supply.

Water availability

The Mid Motueka River (Woodmans to Wangapeka) has reasonable water allocation potential.

The Upper Motueka River (upstream of Wangapeka to Motupiko) and Motupiko catchment is almost fully allocated and there is demand for more water.

The Riuwaka groundwater zone is fully allocated and the Umukuri groundwater zone is fully allocated. In the King Edward zone, the total allocation appears to be under the limit, but in this zone an over allocation for commercial use types is compensated by the lack of use of the reservations for public and private community supplies and institutional/recreational takes. All other zones have room for further allocations.

Landcare research report  - Motueka River

The Motueka and Riwaka Catchments ICM Technical Report 2003

Motueka River Geology

Nutrient Loading Report

State of the Environment - River Water Quality in Tasman District 2015.pdf (pdf 33 MB)

Motueka Ecological District Report April 2014.pdf (pdf 2.7 MB)

Broad-scale intertidal habitat mapping of estuaries of the Motueka delta and Ruiwaka (2019).pdf (pdf 7.6 MB)

Shorebirds of Farewell Spit, Golden Bay and Tasman Bay (2013).pdf (pdf 1.4 MB)

2023 Water Quality Trends in Rivers of Tasman technical report.pdf (pdf 2.3 MB)

2021-22 Bathing Water Quality Summer Season Report.pdf (pdf 571 KB)

Motueka Riwaka Plains Groundwater Model 2019.pdf (pdf 51 MB)

Motueka Riwaka Plains Groundwater Quality Survey 2019 Technical Report.pdf (pdf 6.4 MB)

Tasman Valley Stream E.coli Investigation 2019.pdf (pdf 897 KB)

2021-05-04 Te Mana O Te Wai - Te Tau Ihu Collaborative Project - Council Overview - Tasman District Council.pdf (pdf 1.4 MB)