A man-made weir on the Hokio Stream controls the height of Lake Horowhenua.
A man-made weir on the Hokio Stream controls the height of Lake Horowhenua.
Residents neighbouring a proposed new wetland want an assurance it won’t lead to an increase in groundwater levels in the region.
Detailed plans of the new Arawhata wetland complex proposal have been released, with Horizons Regional Council welcoming further community feedback on an initial design.
The aim of the wetland was to improve the water quality of Lake Horowhenua, recognised as one of the most polluted lakes in New Zealand.
The wetland would remove a large percentage of contaminants from lake-bound stormwater and complement a range of initiatives aimed at reducing nitrate levels.
Horizons held a series of public consultation meetings with neighbouring property owners and iwi in recent weeks.
More than 30 residents attended the most recent meeting at Te Takere Te Takeretanga o Kurā-hau-pō.
Neighbouring dairy farmer Don Hayes said the region’s groundwater and stormwater system was complicated, and any alterations had the potential to impact property owners as far away as Waitārere Beach.
“I feel like they’re trying to ram this through. I fear there will be widespread flooding events,” he said.
“What are they trying to achieve? The lake is also fed by artesian groundwater springs that have high nitrate levels anyway.
“I just need to see the science.”
Frits Van Geldorp farms 13 acres on Hokio Sands Road and said he wanted to see the results of robust hydrolysis testing to put his mind at ease, and an upgrade to culverts within the catchment to mitigate the potential impacts of flood events.
Horizons Governance Group co-chair Rachel Keedwell said all community feedback would be taken into consideration before final design plans were adopted.
“We are committed to working through and understanding possible impacts, as well as working with neighbouring landowners,” she said.
“We understand there are concerns about what a wetland complex might do to worsen those issues, and so careful consideration has been, and will continue to be, given to that in the design process.
“Overall, the meetings have been really helpful as we’ve heard a range of perspectives, including a lot around the current issues with groundwater and drainage in the area during a very wet year.
“The additional feedback we’ve received at these meetings will allow for further refinement of the proposed wetland complex, which is great.”
The group aimed to have a consent application lodged by mid-2023, with the first stage of the wetland built by 2025, she said.
The project, estimated to cost $12.5 million, received $11.2m of Government funding in 2020, with a deed of funding signed in February 2021.
The site of the proposed new Arawhata wetland. Photo: Horizons.
Since then, 142ha of low-lying land that had previously existed as a wetland was purchased from local farmer Geoff Kane for $6.75m to serve as the site for the wetland feeding into the lake.
Keedwell said a lot of work had gone into completing the conceptual wetland design.
“The design has been developed with wetland experts Jacobs, Niwa, and Tonkin + Taylor, as well as a mātauranga ropu established with Muaūpoko Tribal Authority and the Lake Horowhenua Trust,” she said.
“Including these parties has meant that a wide range of perspectives have been included, and Te Mana o te Wai has been at the forefront.
“The initial phase of the project will incorporate at least 15 hectares of the land that Horizons was able to purchase last year thanks to the Jobs for Nature funding, and will have the ability to add further to the wetland in the future.”
The wetland complex aimed to reduce the amount of nitrogen, sediment and phosphorus entering Lake Horowhenua, and improve its water quality.
“The recent completion of the master conceptual design for the wetland complex is an exciting step towards improving the water quality of both Lake Horowhenua and the catchment,” she said.
Horizons had provided information online and continued to welcome feedback through a dedicated website.
The proposed wetland design is available for viewing on the Horizons website.
“The page includes the conceptual design, and a number of scientific reports which have been completed for the Waiopehu Freshwater Management Unit that have been used to inform the development of the conceptual design.”
“The page also has detail on the wider suite of completed and in-progress interventions for the catchment which the wetland adds to. This includes the constructed sediment trap, Hōkio Stream fish pass, and weed harvesting to address water quality and aquatic health within Lake Horowhenua.”
