The Aorere / West Coast FMU extends from Parapara Inlet to Onetāhua/Farewell Spit in the east and north and along the Tasman Sea coastline to Kahurangi Point in the west. The Aorere River is the largest river in the FMU and has one of the highest flows in the Tasman District.
This FMU is dominated by the mountainous forested areas of Kahurangi National Park but land use in the lower valleys is predominantly farming, including sheep and beef and dairying. Collingwood is the largest town on the coast and population is low across the FMU. The FMU also includes highly significant wetlands and estuaries in coastal areas including the Ruataniwha and Whanganui Inlets and Farewell Spit.
Water quality in the FMU is generally good. The main issues are around E.coli concentrations in lower parts of the catchment, including on the Aorere River, and poor water quality of some small streams flowing from farming catchments. There is generally low pressure on water resources due to the high rainfall and plentiful availability, although there has been a slow increase in demand for irrigation in the Aorere River Valley to meet short dry periods during the summer.
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, lakes, springs and wetlands, and provides for our agriculture, tourism, commercial and industry sectors. Our urban development connects us to our backyard waterbodies.
It is 2055, our communities and livelihoods are resilient to our changing climate, and 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.
Our wetlands and estuaries are world class habitats for threatened species and migrating birds.
Healthy freshwater ecosystems support our rural communities and businesses; in return our rural communities and businesses support healthy freshwater.
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These are the key freshwater challenges of the Aorere FMU:
The FMU experiences high annual rainfall. The lower Aorere Valley receives 2.5-3.0 metres of rainfall annually and the upper valley can receive up to 5 metres in some years.
The eastern mountain range (Haupiri) separates the catchment from the rest of Golden Bay. The Wakamarama Range (created by the Whakamarama Fault) separates the Aorere valley from the west coast, with the Burnett Range separating the Whanganui Inlet from the eastern coastal settlements.
The Aorere FMU has some of the oldest geology in New Zealand. This includes:
Farewell Spit is 34km long and one of the longest natural sandspits in the world.
Acidic Orthic Brown Soils (“pakahi soil”) dominates much of the Aorere valley and lies on top of alluvial deposits that infill the Valley floors. Outwash deposits from the adjacent Hills occur along the coast between the Ruataniwha Inlet and towards Puponga these are inremixed with caostal sand depostis at the coastal margins.
The Aorere River is one of the largest rivers in the district and has a catchment of 681 ha. It flows from the alpine regions of the Kahurangi National Park through steep rock gorges before discharging into the flat valley area of the Aorere Valley and out into Golden Bay through the swampy Ruataniwha Inlet. At the Devils Boots site, on the upper part of the river, it has a mean flow of 69,274 l/sec, median flow of 31,816 l/sec and a 7 day mean annual low flow of 11,300 l/sec. The river historically experiences dramatic rises in river flow and flooding.
Tributaries of the Aorere which join the river upstream of Bainham (including the Kaituna, Boulder, Slate, 15 Mile, 17 Mile, and 19 Mile Creeks) flow from the steep bush clad Wakamarama Range. Some of the smaller streams flowing into the Aorere (such as Clay Creek) may dry up in summer.
To the west of the Aorere, there are several catchments flowing to the west coast, including the Patarau, Webb Stream, Anatori, Turamawiwi, Anaweka and Big rivers.
It is estimated that about 30% of wetlands remain in the valley floor, lowland and gentle hill country with about 55% remaining in the west coast part of the FMU. Almost all the alpine wetlands remain.
The Mangarakau Swamp is the largest wetland in Tasman District (at 350ha) located south of the Whanganui Inlet. This swamp is the largest freshwater wetland in Tasman District (at 350ha). It is located south of the Whanganui Inlet and is in a relatively pristine state. Along with other smaller wetlands in the catchment the swamp enhances the ecological and landscape values of the inlet. Although some parts of these wetlands have been subject to moderate levels of modification, such as drainage ditches, most remain in relatively healthy condition.
Most of the pakihi of Tasman District occurs in this FMU, particularly on the southern side of the Aorere valley and atop the Wakamarama Range, and covers an area exceeding 1500ha. The vegetation is dominated by mānuka shrubland containing species such as tamingi, tangle fern, and a variety of sedges and rushes. Small carnivorous sundew can be found in abundance along track edges and thrive in previously cleared areas of the landscape.
Small, ephemeral wetlands and flax swamps are scattered throughout the region. These ecosystems are now critically endangered due to historic drainage. Narrow coastal communities like dune slacks and deflation hollows are found toward the coast and support unique plants important for dune formation, pīngao and sand sedge.
Most of the lakes in this FMU are shallow coastal lakes and include: Island and Dune Lakes near Wharariki Beach, Whupa and Tinawhu/Kaihoka Lakes north of Whanganui Inlet and Lakes Mangarakau and Othuie south of Whanganui Inlet. Boulder Lake in the Kahurangi National Park is the most prominent high altitude lake.
The main aquifer is in the Aorere valley river alluvial terraces. It is unconfined/semiconfined (leaky), generally flows to the northeast, and its water bearing gravels are between 6 – 20 m deep. The Aorere River provides considerable recharge. Away from the river, the aquifer is recharged from rainfall and localised rivers in the contributing valleys (such as the Kaituna and Slate). Groundwater exits the aquifer system by subsurface flow into Golden Bay and springs in the lower Aorere valley.
Aquifers in the eastern coastal settlements (from Ruataniwha Inlet to Farewell Spit) are recharged from the local rivers/streams with some going dry in their lower coastal reaches in summer. The local aquifers also are recharged from rainfall and overland infiltration.
The inside/south of Farewell Spit is the largest open estuary area in the district at over 10,000 ha of intertidal flats. This area is internationally important for shorebirds and the most important for shorebirds in the district.
The Ruataniwha estuary is located just north of Collingwood and is the receiving environment for the Aorere River. It is a moderately large-sized (850 ha), shallow, well-flushed, seawater dominated inlet. Read more here.
Whanganui Inlet is located 14 km northwest of Collingwood and has an area of 2,744ha. It is 13km long and 2-3 km wide making it the largest shallow enclosed estuary on the West Coast of the South Island. The inlet is a drowned river valley, with numerous small streams flowing into it and is in a relatively pristine state. Read more here.
Forest originally covered the entire Aorere Valley.
Today the majority of the Aorere/West Coast FMU (84%) is in native forest and conservation land. Primary human land use is farming including sheep, beef and dairy, particularly in the Aorere valley. Cow numbers have remained reasonably constant over the last 15 years at around 13,000.
The population across the FMU is approximately 1,300. The coastal settlements are mostly a mixture of farming, permanent residents, tourism related businesses and holiday homes. The largest settlement is Collingwood, with approximately 270 people, and projections do not expect this to change by more than 2% by 2043.
Properties in Collingwood are connected to Council water supply (groundwater piped from a well field in the lower Aorere valley) and a wastewater treatment plant for the township located just west of the main township. Outside of Collingwood, properties source water from bores, rainwater collection or surface water abstraction. They also rely on private wastewater disposal systems such as septic tanks.
About 18 native fish have been recorded in Aorere FMU. Probably the most notable aspects of the freshwater fish community in the Aorere FMU is the presence of brown mudfish in Mangarakau (the only place in all of Tasman District) and the high relative abundance of short jaw kokopu, particularly in waterways on the north-western side of the Aorere Valley. This is probably one of the largest strongholds for short jaw kokopu in Aotearoa. Given the reasonable number of wetlands that remain in this FMU, giant kōkopuare relatively abundant in creeks such as Mackay (tributary of Kaituna River), Wharariki, Ngurua, and Snake (downstream of Mangarakau wetland). Lamprey/pirahau are found in various tributaries of the Aorere (including the Bonny Doon Creek, Kaituna River and Basin Creek) and in the Patarau River. Blue gill bully are a feature of the Patarau River and some small creeks of the northern Whanganui Inlet. Echyridella onekaka is the rarest kakahi/freshwater mussel in New Zealand and is only found in NW South Island in this FMU. Most of the shallow coastal lakes have the kakahi/freshwater mussel Echyridella menzieii that form an important part of the life-cycle of several native fish species.
The interior of the Maungarakau Swamp has a substantially native fern rushland community dominated by species of Baumea and Gleichenia.
Much of the original forest covering the FMU remains. The hillslopes support areas mixed beech-podocarp forest, containing predominantly hard beech with rimu on the drier slopes. Northern rata forest is found in the coastal and limestone areas. Scattered stands of alluvial tōtara forest remain and contain a variety lianes including native clematis, jasmine, and supplejack vine. Many of the towering podocarp support epiphytes like puka and the perching kohukohu.
However, forest used to also cover the valley areas. Kahikatea swamp forest with te pukatea, nīkau palm, and kiekie was once very extensive in the lowlands, and were surrounded by flax and cabbage tree swamp. But less than 1% now remains and now cover only 10% of their former area.
Whanganui Inlet is notable due to its size (2741 ha) and lack of modification in the upstream catchments. It is estimated that 40-60% of the saltmarsh remains and there is very little (4%) macroalgal growth. About a third of the estuary is covered with soft mud. The greatest concern with the estuary is loss of seagrass; 74% (718 ha) lost from 2013 to 2021. The Whanganui inlet is a valuable nursery area for 38 species of marine fish. Around 163 species of estuarine invertebrates are also present at the inlet, which is more than in any other South Island estuary. Of particular interest are three new species of Amphipoda, a type of crustacean. Forty-two species of waterfowl have been recorded at the inlet, including three globally threatened species, the Australasian Bittern (a resident), Black Stilt (an occasional visitor) and Wrybill (one record). The banded rail and variable oystercatcher are also resident at the inlet along with many visitors.
The Ruataniwha inlet is a valuable nursery area for marine and freshwater fish; it has an extensive shellfish resource, and is very important for birdlife. Unfortunately only about 30% of the original saltmarsh remains. Approximately 85% of the 200m margin remains in dense forest, scrub, tussock or duneland with the remainder covered in farmland. However, the mudflats are in reasonable health with very little (3%) macroalgal growth and only about 18.5% of the estuary is covered with soft mud.
Farewell Spit was listed as a wetland of international importance under the Ramsar Convention on 13 August 1976. It is a wetland that plays a major role in the support of food chains and is unique in the extent and type of biota it supports. More than 83 species of wetland birds are regularly recorded at the spit including South Island Pied Oystercatcher, Banded Dotterel, Bar-tailed Godwit, Red Knot Calidris, and Ruddy Turnstone Arenaria. Three threatened endemic plant species are found in the sand-dune communities; sea spurge, Sand Daphne and Pingao.
The undisturbed dunes also provide breeding habitat for colonies of Australian Gannets, Caspian Tern and White-fronted Tern. The spit is also a moulting area for Black Swans, over 25% of the New Zealand population of this species.
With over 80% of the Aorere catchment in native forest there is a lot of clean water to provide dilution for any contaminants running off the remaining land. Most of the rivers and springs have good water quality across key parameters including clarity, nitrate levels, phosphorus, ammonia and E.coli. However there are some areas of concern.
On the Aorere River, E.coli has been recorded at very high levels (95th percentile is 1340 E.coli/100ml over the period of 2016-2023 which puts this river in the in the D band) near the river mouth (at the Le Comte site). While Nitrate and Dissolved Reactive Phosphorus (DRP) concentrations are low (in the A band) at the Le Comte site, nitrate concentrations are likely degrading over the last 15 years to 2021. Water clarity, DRP and Total Ammonia are all ‘very likely improving’. The Macro-invertebrate Community Index (MCI) was in the B band (5-year median to 2022 was 115 MCI units) and no trends detected.
At the Kaituna River at Sollys Road (the lower site) E.coli was also in the D band but likely improving over the last 15 years, along with Total Ammonia and water clarity. The Macro-invertebrate Community Index (MCI) was in the B band (5-year median to 2022 was 119 MCI units) and no trends detected. Compare this to a site on the Kaituna upstream of all farmland that is consistently in the A band (5-year median to 2022 was 139 MCI units) and is in the A band for all other water quality measures.
Considerable effort has gone into reducing the impacts of surrounding land use on the water quality of the Aorere River. Fencing off dairy cows from streams was completed in the catchment by 2013 and between 2006 and 2014 over 23,000 plants were established by the Golden Bay Streamcare Group. Over $1.6 million was also invested in on-farm best management practices to 2015.
From investigations prior to 2015, a number of the tributaries from the Aorere were found to have poor water quality, predominantly those from intensive pastoral use catchments. These include Clay Creek and Mackay Creek which have very high E.coli concentrations, and poor MCI scores. High nutrient load from Mackay Creek have likely to have caused nuisance levels of filamentous green algae on the bed of the Kaituna river at the Solly Rd site each summer in the past. However, more-recently this seems to have improved.
Several shallow coastal lakes in this FMU have important ecological and recreation values, but are at-risk. About 43% and 51% of the catchment of Lake Whupa/Kaihoka West and Lake Tinawhu/Kaihoka East is in farmland respectively, with the remainder mostly in regenerating native bush. These lakes do not have an outlet to the sea but have land-locked populations of banded kokopu. There are early indications of a decline in water quality in both lakes as evidenced by notable increases in cyanobacteria in Lake Whupa and the Sediment Bacterial Trophic Index suggesting that the lakes are moderately nutrient enriched (mesotrophic to eutrophic).[5] Further monitoring on these lakes is therefore a priority.
Dune and Island Lakes in Wharariki Farm Park are both likely to be eutrophic (moderately nutrient enriched).
Lakes Mangarakau and Lake Otuihe appear to be in good condition.
Sedimentation, nutrient regimes, faunal composition and the food chains are essentially operating in a natural state in the Whanganui Inlet, although logging in the Wairoa Catchment has increased sedimentation in the inlet and a small rubbish tip near the northern tip of Mangarakau Swamp is a source of leachate to the inlet.
Overall, groundwater in the Aorere/West Coast FMU is of good quality. The majority of chemical parameters have been measured to be well below the Drinking Water Standards for New Zealand 2005 for both the health significant maximum acceptable values (MAV) and aesthetic factors guideline values (GV).
However, localised contamination of Escherichia coli (E.coli) was common in shallow groundwater sites, both for the inland and coastal sites. The majority of shallow sites (wells or driven bores), regardless of their location (coastal or inland), exceeded the MAV for E.coli. This is potentially due to inappropriate siting of the bore/well and/or poor protection of the bore/well head. Groundwater abstracted from deeper in the aquifer (bores deeper than 10 m below ground level) did not have detections of E.coli at the time of sampling.
The total suspended solid load from the Aorere River to the coast is considered low-moderate when compared across New Zealand. Nutrient loads to Golden Bay are relatively low. However, the Ruataniwha Inlet where the Aorere discharges to has only been assessed as having moderate condition due to high disease risk, and moderate muddiness and habitat loss.
Due to the high annual rainfall totals there are very few water availability issues in this FMU although there has been a slow increase in demand for irrigation in the Aorere valley to meet short dry periods during the summer. The main river of the FMU is the Aorere River with a 7 day Malf of 10.8 m3/sec. Other significant rivers in the FMU include the Kaituna, Brown, Clark, Boulder and Slate Rivers that flow into the Aorere. To the south of the Aorere there is the Parapara River which flows into the Parapara Inlet.
The Kaituna River in Golden Bay/Mohua has also recently been identified as possibly over-allocated (18.8% of the 5 yr 7 day low flow) relative to the more conservative default policy >10% of the 5yr 7 day, but is below the current lower default policy of 33 % of the 5yr 7 day low flow. Both a review of the allocation and consideration of allocation portion is to be undertaken as part of the Aorere Water Resources Investigation due in 2024/25 once sufficienct hydrological data is available.
There are numerous small streams that drain to the coast between Collingwood and Puponga and some of these dry up in their lower reaches in summer. Streams that drain into the Wanganui Inlet may also dry up in their lower reaches in summer. Other significant rivers are those along the west coast. The largest of these are the Patarau, Anatori Turimamiwi, Anaweka and Big rivers. These west coast rivers drain the rugged terrain to the west and all flow into the Tasman Sea. Water demand is minimal here apart from stock use in the farmed reaches.
State of the Environment - River Water Quality in Tasman District 2015.pdf (pdf 33 MB)
Aorere River Project Landcare Prize Winner
Good Practice Guide (No. 2) for Managing Wetlands.pdf (pdf 3 MB)
Broad Scale Habitat Mapping of the Whanganui Inlet - 2016.pdf (pdf 2.5 MB)
Whanganui 2021 Seagrass report.pdf (pdf 4.2 MB)
Broad Scale Habitat Mapping of Ruataniwha Inlet (2015).pdf (pdf 2.6 MB)
2023 Water Quality Trends in Rivers of Tasman technical report.pdf (pdf 2.3 MB)
Review of current and past health of Ten Tasman Lakes 2023.pdf (pdf 4 MB)
Technical Report Aorere West Coast Groundwater Quality Survey 2021.pdf (pdf 2.5 MB)
