Our Waitarakao Washdyke Lagoon Catchment

Waitarakao Washdyke Lagoon

Our lagoon needs help. Let's make a plan.

Waitarakao Washdyke Lagoon is a special place for wildlife and mahika kai food gathering, but now it's in decline and the habitat for plants and animals has degraded.

Department of Conservation, Environment Canterbury, Te Rūnanga o Arowhenua and Timaru District Council have joined together to make a plan to restore the health of the lagoon and its wider catchment – and we want your help to make sure we get it right.

Why a plan is needed

Waitarakao Washdyke Lagoon is a significant wildlife sanctuary and a special place for mana whenua, local people and visitors from all around the country.

It was once an abundant mahika kai food gathering hub for local mana whenua and visiting iwi from all over the South Island Te Waipounamu. Tuna (eel), kanakana (lamprey) and all sorts of fish and shellfish were plentiful.

In recent decades however, the lagoon has shrunk and its health and the habitat of the wildlife is declining. Coastal flooding and erosion, and the impacts of climate change, are a risk to the lagoon and to property, farmland and industry in the wider catchment area.

Improving the mauri (life force) of the lagoon will take cooperation across many agencies, organisations, groups and stakeholders. That's why we want the whole community to get involved in creating a strategy to plan for the future of this special place.

How to get involved

To get involved, sign up for future updates (click 'Stay Informed') as we develop Our Waitarakao Washdyke Lagoon Catchment strategy.

Our lagoon needs help. Let's make a plan.

Waitarakao Washdyke Lagoon is a special place for wildlife and mahika kai food gathering, but now it's in decline and the habitat for plants and animals has degraded.

Department of Conservation, Environment Canterbury, Te Rūnanga o Arowhenua and Timaru District Council have joined together to make a plan to restore the health of the lagoon and its wider catchment – and we want your help to make sure we get it right.

Why a plan is needed

Waitarakao Washdyke Lagoon is a significant wildlife sanctuary and a special place for mana whenua, local people and visitors from all around the country.

It was once an abundant mahika kai food gathering hub for local mana whenua and visiting iwi from all over the South Island Te Waipounamu. Tuna (eel), kanakana (lamprey) and all sorts of fish and shellfish were plentiful.

In recent decades however, the lagoon has shrunk and its health and the habitat of the wildlife is declining. Coastal flooding and erosion, and the impacts of climate change, are a risk to the lagoon and to property, farmland and industry in the wider catchment area.

Improving the mauri (life force) of the lagoon will take cooperation across many agencies, organisations, groups and stakeholders. That's why we want the whole community to get involved in creating a strategy to plan for the future of this special place.

How to get involved

To get involved, sign up for future updates (click 'Stay Informed') as we develop Our Waitarakao Washdyke Lagoon Catchment strategy.

  • Next steps - Phase Two community workshops

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    We have wrapped up Phase One of the Our Waitarakao project, where our team got out in the community to find out what you think is important about the Waitarakao Washdyke Lagoon catchment. We enjoyed hearing your ideas and feedback on how the area could be improved.

    Conversations with the community at the drop-in events and stakeholder meetings, along with online survey submissions, indicated an overwhelming level of support towards the project. More than 100 people, businesses and organisations registered their interest to be involved in community workshops to help develop a strategy to restore the health and mauri (lifeforce) of the lagoon and catchment.

    As we enter Phase Two of the project, our team will be holding three half-day workshops in October and November. The group attending the workshops has been selected to include a diverse range of individuals, groups, organisations and stakeholders to represent the Timaru community. Using this combined knowledge and insight, the feedback gathered from these events will inform the development of the draft strategy for the catchment.

    Our team will keep you updated as the project develops. To stay informed follow the Our Waitarakao facebook page, or keep an eye on this website.

  • Community feedback - what you told us in June/July 2023

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    The South Canterbury community has provided a wealth of information, ideas and stories to Our Waitarakao – a project to help restore the health of the Waitarakao Washdyke Lagoon catchment.

    The project team was pleased with the positive level of response to the project, with great turn-out to community events and visits to the Timaru Artisan Farmers Market stall, 170 surveys completed, as well as more than 90 ‘ideas and stories’ submitted during June and July 2023. There was also strong interest from businesses, landowners and groups in the area. The information gathered will be used to help inform the next steps in creating the strategy.

    The wider Timaru community was very supportive of raising awareness of Our Waitarakao, co-hosting additional events to highlight the importance of improving the health of the area, including displays and activities at the South Canterbury Museum, South Canterbury EcoCentre, Timaru Library, articles in the local media, planting events and even beach clean ups.

    Here’s some of what the community shared with the Our Waitarakao team, including comments (shown in italics) from survey and event participants. You can also take a look at a summary here.

    Our Waitarakao Washdyke Lagoon Catchment

    Results from all feedback - including events, surveys, and meetings – was overwhelmingly supportive of the creation of a joint strategy to restore the health and mauri (lifeforce) of the lagoon and catchment. This was reinforced by more than 100 people, businesses and organisations who offered to be involved in future community workshops to help develop the strategy.

    “The lagoon needs to be protected from human impact. Any human benefit from the lagoon should be because it is protected and healthy, not exploited.”

    People visit the lagoon for many reasons

    Waitarakao Washdyke Lagoon is a special place for wildlife and mahika kai (traditional resource) gathering and it is also a popular place for recreation, education and improving our health.

    From the community survey, walking and exercising are the most popular reasons for visiting the lagoon, closely followed by visiting the rockpools on the basalt reef. There were many other reasons for visiting - showing that it has many uses including birdwatching, whitebaiting, school trips and meditation.

    “It is a cool place to be one with nature and look out to the sea.”

    “It's a taonga for Kati Huirapa.”

    “It is a breath of fresh air. It is beautiful on a stormy day, scenic, full of noise from bird chatter, waves and smells, a treasure. It is refreshing. It is utilised for bird watching, walking, fishing, photography, sunrises watching, field trips and general recreation.”

    The community was also asked in the survey what specific features within the lagoon area were important to them. The top answers were:

    • It's a Department of Conservation Wildlife Sanctuary to help protect endangered native and migratory birds, aquatic life and rare plants;
    • The catchment has many small streams feeding into the lagoon, which are important for supplying freshwater and providing habitat for fish and other animals;
    • It's part of a coastal walkway that links up with Caroline Bay;
    • It provides an important link along a network of coastal wetlands in Canterbury for migratory birds and animals; and
    • It has accessible rockpools which people can visit to explore and look at many interesting sea creatures.

    The decline of the natural environment was the key concern

    Across the different types of feedback, people were most concerned about the decline of the natural environment of the lagoon and the wider catchment area.

    In the community survey, the top four areas of concern were: loss of wetland and plant habitat; declining water quality in the lagoon from urban and rural activity; erosion of the beach, lagoon and coastal land; and disturbance of bird nesting areas from motorised vehicles, humans and dogs.

    There was also a lot of feedback that people have experienced litter and rubbish when visiting the lagoon.

    “(It is) particularly important for humans, animals/birds to cohabitate in safe, healthy and secure environments. From living in close proximity to the lagoon I became very interested in the abundance of birdlife. Somehow we need to stop its decline, particularly not allowing it to get any smaller.”

    People want improved access to the lagoon area, better information and education

    Feedback from the community showed a demand for better access to the lagoon area as well as increased educational signage and information. For those surveyed that had not visited the lagoon, the biggest reason was because they didn’t know how to gain access (there is foot access from Bridge Rd, the Coastal Path (currently closed) and Aorangi Road). Some people also commented that they didn’t know that the lagoon was a wildlife sanctuary or accessible to the public at all.

    There was also strong interest in improving walkways and cycleways in the area, as well as linking these to other key active transport networks.

    The importance of the basalt reef rock pools, as an educational opportunity and special place, was also highlighted in many comments.

    “With a wetland area so close to a city centre, I think there should be a focus on conservation and restoration, with regional plans reflecting this over industrial and agricultural interests.”

    “More visual displays near the lagoon/walkway entrance explaining traditional (Māori) usage of Waitarakao Lagoon for kaimoana etc. Information on types of birdlife/wildlife that can be seen, near the site too.”

    “I had no idea of this wonderful taonga so close to Timaru. Always thinking it was part of the Washdyke industrial area. Keep up the good work raising awareness of this!”

    “The ‘Our Waitarakao’ project is a great opportunity for people to see the importance of wetlands in the past and for the future. Schools are interested in their local area and this project fits in nicely with kaitiakitanga – being guardians of natural sites and the organisms that live there. Climate change and the effects on our coasts is also important for our young people and their whanau to learn about. This project can help highlight this information”. - Keely Kroening, South Canterbury Museum Educator.

    Business, industry and landowners are eager to improve the health of the area

    Engagement with businesses, industry and landowners indicated a high level of interest in getting involved in future actions to improve the catchment – and many already had ideas about how they could make a positive difference to the environment.

    Thirteen stakeholder meetings, including with farming catchment groups, irrigation schemes, businesses and non-profit organisations, were held during the engagement phase to introduce the strategy and gather ideas and information. All meetings were positive and highly productive, with a willingness from all to contribute ideas, feedback and knowledge of the catchment area – including thoughts on flood protection, enhancing wetlands and environmental compliance. The meetings also led to requests for future presentations to other interested groups.

    “Establish a sustainability collective made up of business/industry and other key stakeholders to support the delivery of agreed science-based environmental outcomes and deliver on business sustainability goals.”

    Next steps for Our Waitarakao

    The project team and its steering group will now use the feedback and knowledge gained through this engagement with the community to help inform the next steps of creating the strategy. This will include some additional focused community and stakeholder workshops looking at different ideas for improving the health of the area, as well as how to measure success. A draft strategy for the lagoon catchment will then be drafted and available for feedback in the first half of 2024.

    About Our Waitarakao

    'Our Waitarakao' Washdyke Lagoon Catchment strategy is a partnership between Te Rūnanga o Arowhenua, the Department of Conservation, Environment Canterbury, and Timaru District Council to plan for the area’s future by addressing problems with water quality, wildlife habitat, flooding, erosion, and the impacts of climate change.

    The strategy will be for the whole catchment area, as activity in the wider area impacts the health of the lagoon through the many streams, drains and neighbouring businesses, farms, and properties. There are also emerging issues across the catchment area with flood protection and the impacts of climate change that are likely to be part of the strategy.

    For more information and to join the e-newsletter, click the 'Stay Informed' section of this webpage.

  • Our stories

    Young Farmers' planting day

    10 July

    More than 1,000 natives were planted in the Waitarakao catchment on Saturday 8th July, thanks to a collaboration with local farmers Kevin and Karen O’Kane, and the contestants from the Young Farmer of the Year competition and their families.

    A drizzly morning did not deter planting efforts, with 60 people getting involved. We look forward to watching these plants grow and enhance the biodiversity of this catchment.

    Community involvement ramps up

    15 June

    More than 40 people attended a drop-in event at C-Bay Caroline Bay Trust Aoraki Centre on Tuesday evening (13 June). This was a chance to chat with the team, ask questions, and share stories and ideas for the future of the threatened coastal lagoon, and wider catchment.

    It followed a similar event at the Timaru Artisan Farmers Market on Saturday. Many braved the chilly morning to find out more the project – and the free, Our Waitarakao bags were a bit hit.

    Our Waitarakao project lead, Chris Fauth, says some great conversations are being had - kicking of several months of engagement.

    “We’re really enjoying hearing what people like about the environment at Waitarakao. There’s a wide range of interests, including around natural hazards, water quality and environmental quality – both in the lagoon and up the streams.

    “What’s impressed me is we’ve had lots of people asking what actions they can take, and how they can get involved.

    “This is the start of what will be a big process, and it’s been really positive so far.”

  • Strategy process, scope and objectives

    Over the next year – and with multiple opportunities for input from the community and stakeholders – the Our Waitarakao Washdyke Lagoon Catchment strategy will be created for the whole catchment and will outline the actions needed to ensure a healthy future for this area.

    The vision of the strategy is: to restore the mauri (health/lifeforce) of Waitarakao for everyone.

    Our Waitarakao is guided by both a Working Group and Steering Group, made up of key staff and representatives from partner organisations.

    Collectively, we have agreed the process and scope of the strategy, and also come up with proposed objectives to achieve the vision.

    Strategy process

    Strategy scope

    We want to work with the community to identify suitable and realistic options for restoring the health of the lagoon, at the same time as planning for change. The strategy will deliver both short and longer-term options to proactively address issues impacting the catchment and anticipate future actions.

    There are policies and legislation already in place for Waitarakao Washdyke that you may be aware of - such as Environment Canterbury’s Land & Water Regional Plan, Timaru District Council bylaws, the Wildlife Act 1953, and Mātaitai Reserve bylaws, to name just a few. Our Waitarakao Washdyke Lagoon Catchment Strategy will consider existing legislation and link in with other relevant plans being developed - to identify what else is needed to ensure a better future for the lagoon.

    Once the strategy is created and approved, it will be implemented into a non-statutory plan, with functional stages, actions, and requirements for future funding. Information gathered as part of the Our Waitarakao strategy will help inform future local and regional planning processes.

    Our Waitarakao will be:

    • an opportunity to carefully consider many issues including natural hazards and climate change adaption, mahika kai/resource gathering, water quality, biodiversity and wildlife habitat, ecosystem health, land use, access and education
    • for the whole catchment including the lagoon, nearby coastal flats, farmland and streams
    • driven by a partnership between Department of Conservation, Environment Canterbury, Te Rūnanga o Arowhenua and Timaru District Council, with representation from the Orari Temuka Opihi Water Zone Committee on the Working Group
    • a process where all members of the community are given opportunity to contribute ideas and feedback across multiple phases of engagement
    • about planning for the future but does not include implementation. It will form the basis of a subsequently-developed implementation plan
    • a non-statutory document, but some of the options and outcomes are likely to assist partner agencies to meet statutory requirements

    Proposed objectives

    Here are proposed objectives for Our Waitarakao Washdyke Lagoon Catchment. These may be refined to reflect community feedback, before being confirmed later this year.

    - Enable customary harvest of food/resources that were traditionally gathered from the area in and out of the water. Acknowledging and improving access rights for the purpose of mahika kai.

    - Ecological revitalisation or restoration to achieve a thriving, healthy, functioning ecosystem.

    - Proactive identification of current and future climate events and hazards. And specifically plan how we will adapt to coastal hazards to achieve the other objectives of the strategy.

    - Advocate that new and adapted infrastructure is determined by climate change with mauri (health and lifeforce) of Waitarakao at its forefront.

    - Plan for the management of freshwater flooding that enters this catchment for the benefit of the mauri of Waitarakao and the values of this strategy, as well as for the protection of people and property.

    - Understand how the hydrology/water balance of the whole catchmentimpacts our ability to achieve the values and objectives of this strategy. Where necessary action change to achieve objectives.

    - Enhance community understanding and awareness of the Waitarakao Washdyke environment, enabling all our community to interact with the catchment through promotion, learning opportunities and appropriate physical access.  

    You can give feedback on these proposed objectives by taking our survey.

  • Summary of the catchment area

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    Waitarakao Washdyke Lagoon is a brackish, shallow, coastal lagoon north of Tīmaru on Poupou-a-Rakihouia (the South Canterbury coastline).

    It is a nationally significant wildlife sanctuary for birds, plants, and fish. It is also a special place for mana whenua, for local people to visit and explore the rock pools, and for visitors from all around the country - including birdwatchers and geologists.

    The wider catchment includes important infrastructure, business and industry, mātaitai reserves, streams and rivers, farming and residential homes.

    The lagoon catchment is vulnerable to natural hazards, climate change impacts, and land-use pressures, which has led to an ongoing decline in ecosystem health and increase in hazard risks.

    Waterways flowing to the lagoon

    The lagoon is a well-known part of Washdyke, Timaru, but the strategy will look at all the areas around it that form the overall catchment. This includes three major streams; Papaka, Rosewill, and Oakwood, and several small tributaries (stream offshoots) which merge into Washdyke Creek before entering the lagoon environment.

    The catchment also includes the Seadown Drainage Ratings District – farmed land extending north along the coastline from the lagoon – and parts of the Levels Plain, which contains groundwater, local run-off and other land use that affect parts of the catchment.

    The industrial area contains a mix of small business, larger commercial and industrial operations, and large-scale storage facilities. Stormwater run-off following rainfall discharges into Waitarakao Lagoon (in some cases via Washdyke Creek) through a combination of piped or open drains.

    The ongoing impacts of land use in the catchment mean we need to collectively take action to make a plan to restore the health of the lagoon and catchment.

  • Natural environment

    The Waitarakao Washdyke Lagoon Catchment is part of a threatened network along the Canterbury coast of lagoons, estuaries, swamps, wetlands, scrub, and remnant patches of native bush.

    It became an official Wildlife Sanctuary Reserve in 1907 and is home – or a stop-off point – to many species of birds, including the tarāpuka/black-billed gull, ngutu pare/wrybill, taranui/Caspian tern, and poaka/pied stilt. Waitarakao is also home to native freshwater species including īnaka/whitebait and the long-fin eel (tuna) which is New Zealand’s largest native freshwater fish. Longfin eels are a taonga species for Māori and swim thousands of kilometres out to near the Tonga trench to complete their life cycle.

    Many of these types of coastal wetland and lagoon environments have been lost in recent history – and those remaining are critical mahika kai environments and unique and important habitats for a range of wildlife and flora.

    Waitarakao Washdyke Lagoon was historically much larger than it is today, with estimates suggesting in 1881 it was around 250 ha in size – it is now is less than 50 ha due to changing land use and development. Other parts of the catchment also contained large wetland or swamp habitats that have subsequently been drained or destroyed through historic land-use.

    The lagoon’s shrinking size means that it’s becoming a challenging place for birds to nest, fish to breed, and delicate plants to grow.

    There is work already underway by community groups and organisations to help control predators and improve habitat, but there is still a lot of work to do.

    Caption: A rare, historic painting of Waitarakao Washdyke Lagoon in 1874

    Mahika kai

    Waitarakao was once a renowned kāinga mahika kai area for mana whenua and the wider Ngāi Tahu iwi and part of a busy coastal travel route between lakes Wairewa and Waitarakao (Washdyke Lagoon) and then further south.

    Waitarakao and the nearby pa was a popular stop-off point for these trips. You could travel light – as there was kai available to catch and eat all along the way. 

    There was a tarakihi breeding area near the lagoon – alongside other stocks of fish/kaimoana including pātiki, shark, kanakana, kina, paua, cockles and crayfish.

    There were also special plants such as kōareare - the edible rhizome of raupō, patete (seven finger or umbrella tree) and karengo sea lettuce.

    These are now hard to find – or not there anymore.

    Despite the lagoon and surrounding parts being officially recognised as mātaitai reserves, overfishing and erosion have had an adverse effect and mahika kai resources have degraded.

    Caption: Another historic painting. Handwritten caption reads: Washdyke Lagoon near Timaru NZ, Oct 1874 - Commencement of Ninety Mile beach

    (Ninety Mile beach refers to a travel route used by mana whenua and wider iwi, extending from Te Roto o Wairewa/Lake Forsyth - in Banks Peninsula, to Waitarakao Lagoon)

    Water quality

    The water quality in the Waitarakao Washdyke Lagoon and nearby streams is poor and not meeting some standards.

    Polluted stormwater is contributing to poor water quality in Washdyke waterways. This impacts on the relationship of Te Rūnanga o Arowhenua with the waterway and Waitarakao Washdyke Lagoon. Stormwater can carry contaminants that impacts the safe consumption of food gathered from the waterways.

    High nutrient concentrations (nitrogen and phosphorus) have been found in the waterways. This is consistent with nutrients from agricultural runoff and surrounding urban activities in the areas. Elevated nutrients can result in algae growth that can harm aquatic life.

    High concentrations of metals (arsenic, zinc and lead) have been found accumulating in the waterways. These can be attributed to surrounding industrial and urban activities in the area, vehicle movements and roofs/building materials.

    Environment Canterbury’s Land and Water Regional Plan and other key pieces of planning legislation require improvements to water quality in the catchment. Timaru District Council’s stormwater management plan consent, and farming land use consents, will help drive improvements - but other initiatives will also be needed.

  • Water flow

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    Waitarakao Washdyke lagoon and catchment - once a thriving network of streams, swamps, and wetlands - has been highly modified over the years. The way in which water moves through the catchment has therefore changed and we now need to review how it will work best in the future.


    Farmland nearest the coast (east of Seadown Road) is supported by a network of drains referred to as the Seadown Drainage Rating District. These drains all eventually feed into the northern end of Waitarakao Washdyke Lagoon and during periods of low or normal rainfall this drainage scheme provides the only regular input of freshwater that flows directly into the lagoon.

    The Seadown Drain is the largest of this network of drains, and flows immediately on the landward side of the coastal stopbank. This drain supports farming to the north of the lagoon and is part of the mātaitai. Its fate is tied to that of the coastal stopbank; when the stopbank is shifted in response to coastal erosion the Seadown Drain must also shift in location. Changes to the drainage scheme will change the whole lagoon’s water flow (hydrology).

    Flows from streams

    The freshwater stream flow input to Waitarakao Lagoon is via Washdyke Creek, which crosses beneath State Highway One. Washdyke Creek is the downstream reach of a number of tributary catchments including Papaka, Rosewill and Oakwood streams.

    These stream tributaries extend as much as 10–12 km west and northwest of the lagoon. The upper parts of the streams are rolling downs or low hill country that is farmed with isolated residential development. The streams exit the rolling hill/gully type parts of their catchments on the Washdyke Flat (traversed by Washdyke Flat and Cartwrights Roads) up-plain of the industrial area. This flat land is riddled with old watercourses and depressions, which will carry flood flows during heavy rainfall events.

    Washdyke Creek (during 'normal' conditions) does not flow directly into Waitarakao Lagoon but is picked up by a ring drain circling the outside of the lagoon and taken directly to the piped outlet point to sea at the south end of the lagoon. When flows in the creek are slightly elevated after rainfall, the creek overtops the ring drain and discharges straight to the lagoon.

    Stormwater inflows

    Stormwater run-off following rainfall will discharge from the residential, commercial, and industrial development land into Waitarakao Lagoon (in some cases via Washdyke Creek) via a combination of piped or open stormwater drains. In major rainfall events, stormwater flooding can impact lower parts of the developed catchment.

    Seawater inputs

    Seawater influences the catchment in multiple ways. High tides push up through the piped lagoon outlet and ring drain and lift the lagoon level (at low tide the lagoon can mostly empty out in a reverse of the same process). In moderate coastal storm/high swell events the gravel barrier between the lagoon and sea can be overtopped and waves will push seawater into the lagoon filling it up. And lastly, in larger/extreme coastal events, seawater can breach or overtop the stopbank to the north (as well as overtopping the gravel barrier) causing more widespread flooding of rural and/or industrial land.

    In any situation where there is an excess of water due to seawater overtopping, heavy or prolonged rainfall (or river and stream flooding) the lagoon will rise. When the lagoon is at high levels, stormwater discharges will back up in the industrial area and the Seadown Drain system will cease flowing to the lagoon and floods. This situation can be alleviated by either a natural or mechanical breach of the gravel barrier to lower the lagoon level (but only if sea conditions allow this).

    Piped outlet

    The catchment currently contains just a single outlet for discharging water to sea; a pipe at the south end of the lagoon. This means all water in the catchment must pass through the lagoon area in its journey to the ocean – including industrial stormwater and farm drainage. The pipe’s location has impacts on the reef environment, and its height above sea level controls the lagoon level and enables the Seadown Drain scheme to function.

    Sea level rise and coastal erosion threaten the outlet’s ability to function as it does currently. Changes to the outlet will have other significant effects on wider catchment hydrology. 

  • Land use - residential, farming and industry

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    Most of the catchment area is rural land with a range of farming activities, as well as lifestyle blocks.

    The inland part has rolling hills that feed onto generally very flat farmland. It's traversed by numerous stream tributaries, drainage and other channels and depressions.

    The smaller, more densely developed part of the catchment houses a major commercial and industrial hub for Timaru, small businesses, residential areas, critical infrastructure, and the lagoon itself.

    With one exception, up until the early 1970s the Washdyke industrial area was still entirely rural pasture land and low land on the fringes of Waitarakao Lagoon. Since the late 1970s and early 1980s, the industrial and commercial hub has grown rapidly into one of the main industrial and commercial hubs of the Timaru district, and economically, is regionally significant.

    The industrial area contains a mix of small business, larger commercial and industrial operations, and large-scale storage facilities. Some businesses directly link into the port via the railway which extends through the area. The industrial area contains critical infrastructure including State Highway One, the Main South Railway Line, and Timaru’s main wastewater treatment ponds.

    The industrial centre of Washdyke is protected from freshwater flooding from Washdyke Creek by a flood protection scheme including stopbanks.

    The catchment also contains some higher density residential development. The densely developed part of the catchment discharges stormwater into the lagoon, and relies on the lagoon for a natural buffer against sea or freshwater flooding. In future, this part will become increasingly at risk of natural hazards like coastal inundation and erosion.

    Residential areas located on the west side of State Highway One which, although elevated above most of the catchment, discharge stormwater to Waitarakao Lagoon and Washdyke Creek.

    There are also smaller pockets of residential development within the commercial and industrial areas.

  • Flooding and erosion

    Natural hazards like flooding and erosion negatively impact humans, animals, and the environment.

    For Waitarakao, the key natural hazards are coastal erosion, seawater flooding and freshwater flooding. These all have a big effect on the catchment.

    Coastal stopbank

    An approximately 7 km-long coastal stopbank runs parallel to the coast from the northern margins of the lagoon to Beach Road. It was built in the mid-1980s, after an earlier version was compromised by coastal erosion.

    The stopbank is managed by Environment Canterbury on behalf of a small rating district made up of farm owners to the north of the lagoon, and mostly eastward of Seadown Road. Those in the rating district also contribute to the maintenance of the drainage scheme and management of the piped outlet to sea, at the southern end of the lagoon.

    The stopbank protects the land behind from seawater flooding and also protects the Seadown Drainage Scheme – the main drainage channel which runs parallel to the stopbank.

    Caption: A 7 kilometre-long stopbank protects the Seadown Drainage Scheme and farmland behind

    The stopbank does not protect against erosion and it can't stand up to ongoing and direct wave action. Erosion is now beginning to encroach on this stopbank to the extent that it's reaching the end of its lifespan, and risks being breached.

    Caption: Erosion is bringing the sea closer, making it easier for damaging waves to reach the stopbank

    Because the Seadown Drain is located immediately landward of the stopbank, the fate of the stopbank and drain are linked - if one is moved or changed, the other must be moved also.

    Coastal erosion

    The coastline in this catchment is eroding at an average rate between around 1.7m to 2m per year. There can be periods of slow erosion, followed by shorter bursts of significant erosion during and after a storm.

    The coast has been eroding throughout recent history, but the rate accelerated significantly after the first Timaru Port breakwater was built in the 1870s. The breakwaters restricted the movement of sediment from the south – starving the Waitarakao/Washdyke beach of gravel.

    Caption: Blue lines showing past shoreline positions indicate the extent of erosion of this coastline

    Erosion has caused the Waitarakao Washdyke lagoon area to reduce by about 90 percent. As the lagoon continues to shrink, its ability to act as a buffer against natural hazards - and as a healthy environment and habitat for wildlife - will be further compromised.

    The effect of erosion and the shrinking of the lagoon is exacerbated by land use and development, which prevents the lagoon from expanding inland or to the north. Old North Road was named as such because it was historically used as the main north road for Timaru, in part because the current State Highway One would be inundated regularly by the lagoon.

    To the north of the lagoon, erosion primarily impacts on farmland, with the historic response being the periodic retreat of the coastal stopbank and drainage infrastructure (and associated loss of private land).

    Seawater flooding

    The lagoon has some capacity to absorb seawater that overtops the beach barrier into this area. The coastal stopbank north of the lagoon also provides some protection against the risk of seawater flooding.

    However, coastal defences (both natural and built) can only handle so much, and in large storms there is a risk of significant seawater flooding into the Washdyke industrial area and onto farmland to the north of the lagoon.

    Ongoing coastal erosion continues to put pressure on, and will eventually compromise, the coastal stopbank, while also shrinking the capacity of Waitarakao Lagoon.

    Sea level rise will increase the potential frequency, depth, and extent of seawater flooding in the area.

    Decisions need to be made around the use of, functionality, and location of potential coastal defences.

    Ōpihi River flooding

    In extreme flood events in the Ōpihi River, it is expected that deep breakout flows will travel into the coastal stopbank then run parallel to the coastline, through coastal farmland, past the Washdyke industrial area and into Waitarakao Lagoon.

    There is currently enough space between the existing coastal stopbank and most built development for this water to reach the lagoon without flooding the Washdyke industrial area, though farmland will be significantly flooded.

    However, as the coastline and coastal stopbank retreat, and development remains fixed in place, the space for the water to reach the lagoon will reduce. The ongoing shrinking of the lagoon also reduces its capacity to absorb such flooding without affecting surrounding development. For these reasons, it is likely the Washdyke industrial area will become at direct risk of flooding from the Ōpihi River in future.

  • Climate change

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    Our climate is changing, and more extreme weather and sea level rise will impact the ability to effectively drain the Waitarakao Washdyke catchment long-term.

    Higher mean air temperatures are likely to raise the water temperature of waterbodies within the catchment. Climate change projections indicate an increase in rainfall intensity in the area, which will increase the occurrence of flooding and stormwater runoff. This will lead to additional inputs of nutrients, contaminants and sediment to the waterbodies. Higher water temperatures will increase the risk to native freshwater diversity as some species are sensitive to temperature increases. Warmer water temperatures could further alter water quality by contributing to algal blooms.

    The coastline of Washdyke Waitarakao is eroding and sea level rise is projected to increase coastal erosion rates.

    Coastal erosion will squeeze and degrade coastal and wetland habitats where geographical constraints or existing land use don’t allow a natural landward migration of coastal habitats. Sea level rise will also increase the frequency and size of coastal storm flooding, increasing the flood risk to built environments, productive land and coastal wetland habitats.

    More coastal flooding will lead to increasing salinity stress to coastal wetlands. Many species of invertebrates, some species of plants, and fish species are specifically adapted to coastal wetland conditions and cannot tolerate large changes in salinity. This could result in a loss of biodiversity and/or changes to the composition of wetland species.

Page last updated: 17 Oct 2023, 12:53 PM