Our Waitarakao Washdyke Lagoon Catchment

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.

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.

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 catchment impacts 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.

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.

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).

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.  

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.

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

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

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

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

Seawater flooding

Ōpihi River flooding

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.