The existing pond has experienced weed and algae issues since chemicals were stopped being used in the early 2000s.

Since then the Council has been working on a variety of solutions to resolve this issue, but these investigations have been complex, protracted and expensive. A permanent solution is needed to minimise the ongoing costs to the Nelson public.

The reserve will have a number of uses, recreational, environmental and cultural.

The reserve will be designed for families, to have a safe and sheltered place to picnic. The areas will be defined by areas of native planting, appropriate to coastal area. They will also include picnic tables, benches, water fountains and barbeques. There is also the option for the model train tracks to be extended.

The estuarine planting area will act as a natural treatment for stormwater flowing into the area.

The area will also have cultural interpretation panels, so that people can learn about the history of the area and its importance to local iwi.

Council has investigated a wide range of options to come up with a solution to deal with the issues arising from the current pond. Part of these investigations has involved talking to iwi, to make sure that we are considering the wider environmental impact of the various options.

Unfortunately, high carbon and construction costs associated with concreting the pond, meant we could not proceed with this option. There were also concerns this option would not sufficiently improve the quality of stormwater that would end up going to the back beach area.

There are a number of options for modellers to sail their boats around the Nelson Tasman region (including Monaco and Saxton). There is also the potential for future pond access at Best Island.

Although the pond has played a part in receiving stormwater discharges in the past, new solutions have been identified to more effectively manage stormwater to improve the quality of this water.

We are looking to use the Hynds ‘Downstream Defender’. This is a specially designed underground chamber that removes and retains gross debris, total suspended solids (TSS) and hydrocarbons from stormwater flowing through our pipes.

Contaminated stormwater runoff flows into the chamber, and creates a low energy vortex flow. This allows solids/sediment to drop down, while floating oils/rubbish rise to the surface. The treated stormwater exits through a submerged outlet chute.

The solids and floating pollutants can then be removed by a sucker truck. A video of how the ‘Downstream Defender’ works can be seen here.

This product has been developed over 30 years, and has been used throughout New Zealand and the world. Hynds have a branch here in Nelson, so the treatment solution is sourced through the local branch.

The Downstream Defender can remove up to 60-90% Total Suspended Solids (TSS) with a mean particle size of 150 microns (about as thin as a human hair!).

More information can be found https://www.hynds.co.nz/product/downstream-defender/

The “Downstream Defender” captures a fair amount of the contaminants in the stormwater, but some may still sneak through.

The stormwater flows from the pipes into a swale planted with native estuarine species. The plants will help further treat the stormwater, and allow for suitable mixing with the estuarine environment. This provides a level of treatment that is far better than anywhere else in our network.

We believe that the proposed active treatment, using the Downstream Defender and the swale planting, will provide a far more environmentally acceptable solution than the passive treatment of a concrete pond.

The aim of the concept design is to provide a solution for the pond that will maintain the current level of flood protection for the area (drained by the Golf Road stormwater catchment).

This design will help the Centennial Park pump station to operate at its full capacity during spring tide sea levels at Tahunanui. It will also be able to deal with the impacts of sea-level rise and increased rainfall (under median range for RCP 8.5 to 2055 – https://niwa.co.nz/our-science/climate/information-and-resources/clivar/scenarios)

The discharge channel will be sized to receive and discharge 100% current design flow from Centennial Park pump station.

By changing the area to a recreational area, the overflow from Centennial Park pump station becomes part of the stormwater network. Therefore provided the discharge can meet the set standards this discharge is permitted and consent isn’t needed.

The public had an opportunity to make formal submissions through the 2021 - 2031 Long Term Plan consultation process. We are always happy to receive any feedback during the project.