A treatment train, an upgraded culvert and stormwater diversions all feature in the council’s detailed plan designed to convey stormwater from the Meadowstone subdivision to Lake Wānaka without flooding precious creeks or private properties.

But a prominent water advocacy group is questioning whether council’s engineered solution is up to the task to divert all the stormwater and ensure it’s clean when it enters Roys Bay.

The design process of the Stone Street stormwater plan to alleviate the ongoing flooding of Bullock Creek is complete, Queenstown Lakes District Council (QLDC) announced recently.

QLDC Stone Street stormwater project manager Simon Brackstone said the complexity of the design meant the design process took longer than anticipated. 

As a consequence, its budget also increased from $1.6M (indicated in last year’s 10-year plan) to $4.48M in the current annual plan.

The stormwater plan

Stormwater runoff from the neighbouring Alpha Series residential subdivision has inundated Bullock Creek on numerous occasions since the subdivision was constructed in 2017.

Council has acknowledged Bullock Creek’s sensitive trout habitat and wetlands and the primary purpose of the new stormwater plan is to protect Bullock Creek by diverting stormwater from both the Alpha Series subdivision (Meadowstone) and Upper Stone Street that currently discharges into the creek, Simon said.

Stormwater overflows the Alpha Series retention pond, depositing sediment into the neighbouring Bullock Creek.

It will also provide some flood protection to houses and properties alongside Bullock Creek, improve the treatment of the stormwater before it’s discharged to the lake, upgrade the undersized Middle Creek culvert under Mt Aspiring Road, and facilitate better pedestrian and cyclist active travel links in the Wānaka A&P Showgrounds area.

“Applications for consent for earthworks and to work in proximity to water bodies have been lodged with the Otago Regional Council and the QLDC,” Simon said. These consents are required before construction can begin.

Council has consulted a wide range of interested and affected parties, including iwi, the Otago Fish and Game Council, the Friends of Bullock Creek, Wai Wānaka, the Guardians of Lake Wānaka, and the Upper Clutha A&P Society, he said, and has considered this feedback in the design process.

Friends of Bullock Creek’s concerns

But one community organisation consulted by the QLDC is questioning the long-term effectiveness of this stormwater plan.

A spokesperson for Friends of Bullock Creek (FOBC) said while FOBC had been kept informed of the council’s stormwater plans it has not been involved in the design of the pipeline proposal, nor has it signed an ‘affected party agreement’ for the resource consents.

This QLDC design plan shows the path of the “treatment train” along a Showgrounds’ boundary and the upgraded Middle Creek culvert under Mt Aspiring Road which discharges the stormwater to the lake.

“FOBC remains very concerned that [council’s consultation process] falsely conveys to the wider community that we agree and support the project in its current form,” the spokesperson said.

The group has previously filed a complaint with the Otago Regional Council’s pollution hotline after steady rain released sediment from the Alpha Series holding pond into Bullock Creek.

The council deserves credit for persevering with efforts to solve the flooding and contamination of Bullock Creek “every time it rains”, the spokesperson said, but FOBC remains concerned this plan might only provide a partial solution.

Given that previous engineering-driven solutions to the flooding have not worked, FOBC has a number of concerns regarding this plan’s design and viability.

Their concerns are reinforced by council’s own resource consent applications which state that the operation of the proposed soakage system may be compromised due to the limited land available at the showgrounds and the system might allow incompletely filtered water to enter Roys Bay, the spokesperson said.

“FOBC is 100 percent committed to solving this problem to deliver the best outcome for Bullock Creek and the waters of Roys Bay.”

Stormwater treatment

These concerns for the quality of water being discharged into Roys Bay were echoed by deputy mayor Calum MacLeod at the Wānaka Community Board (WCB) last week (August 4).

He said QLDC should investigate how it could monitor the stormwater through this new system.

The new system features a ‘treatment train’ comprising a series of bays to treat the stormwater, a forebay where the stormwater velocity is slowed and sediment can settle, followed by four planted swales where the stormwater is filtered through gravels and plants before discharging into the lake, Simon said. 

The treatment train will appear as wide swales located beside the showgrounds' Middle Creek boundary, between the A&P Society’s building and Mt Aspiring Road.

While monitoring of stormwater may be a resource consent requirement, Simon said council also intends to monitor Bullock Creek’s stormwater and “further consideration will be given to monitoring stormwater at the end of the treatment train”.

Concurrent improvements

Construction of the new stormwater system will need to be scheduled around the A&P Show and the fish-spawning season in Bullock Creek, Simon said. 

As a result, a construction programme has not been established “but work could begin this summer, and it is expected take about nine months to complete,” he said.

Subject to the granting of resource consents and funding, the council also intends to upgrade public access to the showgrounds.

Simon said improved pedestrian and cycleway access is incorporated into the design in the form of widening the footbridge across the creek at the end of Lansdown Street, and moving the fence at the back of the Wānaka Lakeview Holiday Park to widen the existing unformed path between Stone Street and the showgrounds.

Funding for this additional work is yet to be resolved, he added.

Middle Creek runs through central Meadowstone and was cleaned and cleared earlier this year, but stormwater diverted into existing underground systems will necessitate a pipe upgrade, and this work will affect roads, such as Stone Street.

“This will result in road disruptions, but we will do our best to keep people well informed about these,” Simon said.

“I think it’s great to use these opportunities when [council is] digging up roads and putting in infrastructure to upgrade other stuff,” WCB member Ed Taylor said. 

IMAGES: QLDC