Akaroa Treated Wastewater Irrigation Scheme
Freshwater and estuary ecology assessment for Akaroa’s shift from harbour discharge of treated wastewater to land-based wastewater irrigation: establishing ecological baselines, evaluating effects on threatened species and sensitive habitats, and presenting expert evidence at resource consent hearings.
2021–ongoing
context
With the current harbour discharge consent due to expire in 2024, Christchurch City Council is looking to a new way of managing Akaroa’s wastewater, by discharging treated wastewater to land instead of into the harbour. The resulting scheme involves a new treatment plant and pump station, and irrigation of highly treated wastewater onto native trees and grass at locations around the inner Akaroa harbour. Whilst the scheme discharges to land there is still the need to consider how it will interact with freshwater streams and the intertidal embayments that these streams ultimately flow into.
challenge
- The scheme interacts with multiple freshwater environments, each with different catchment characteristics, fish communities, and water quality profiles requiring individual assessment. These freshwater systems discharge into embayments around the inner Akaroa harbour, that support nationally At Risk seagrass (Zostera muelleri), and shellfish populations valued as mahinga kai – all requiring careful evaluation.
- Whilst there was some existing ecological data for the waterways, our use of eDNA methods helped us to fill key data gaps. Baseline water quality data in the freshwater streams did not exist at the resolution needed. We designed and implemented a 12-month sampling programme across six sites to help inform the effects assessment and scheme models, as well as acting as baseline data for future monitoring of the scheme.
- With limited data on the intertidal habitats we designed and implemented a sampling programme that would not only inform our effects assessments but also act as the start of a baseline monitoring dataset.
our role
EOS Ecology is the aquatic ecology specialist for ATWIS, engaged by Stantec for Christchurch City Council. EOS is responsible for all components of the freshwater and estuary ecological assessments – from initial gaps analysis and baseline surveys through to production of two AEE reports (freshwater and intertidal ecology), presentation of expert witness evidence at resource consent hearings, and expert conferencing.
how we approached it
- Completed freshwater ecological surveys including instream habitat assessment, macroinvertebrate sampling, electrofishing, and eDNA sampling at 12 sites across all potentially affected catchments – identifying fish communities with multiple At Risk species including longfin eel, kōaro, īnanga, giant bully, bluegill bully, torrentfish, and lamprey.
- Implemented a 12-month baseline water quality monitoring programme (August 2021 to July 2022) across six freshwater sites, collecting monthly data on nutrients, heavy metals, faecal indicators, and physicochemical parameters to inform scheme design and our effects assessment as well as establish the baseline for future monitoring.
- Completed intertidal surveys across three estuary embayments, documenting benthic communities and mapping the extent of seagrass beds.
- Provided guidance around the range within which nutrient concentrations in the freshwater receiving environment should be managed to in order to retain existing values.
- Produced two comprehensive AEE reports – freshwater ecology and estuary ecology – both concluding effects could be effectively managed through scheme design and adaptive management. Prepared and presented expert witness evidence at resource consent hearings, and participated in expert conferencing with Regional Council ecologists to establish agreement on recommended monitoring requirements. The estuary AEE received no Section 92 requests for further information, and the freshwater AEE received only a minor request relating to the presentation of water quality data.
outcome
The assessments established that Akaroa’s shift from harbour discharge to land-based irrigation can be achieved without significantly impacting on the freshwater and estuary environments. A comprehensive monitoring programme with adaptive management triggers will ensure any unanticipated effects are detected and addressed. The final decision on the application will be made alongside a related consent for the Duvauchelle wastewater scheme, enabling cumulative effects on Akaroa Harbour to be considered.
wider impact
- A nationally relevant approach for how small communities can manage wastewater reuse in ecologically sensitive receiving environments – the assessment framework spanning freshwater, estuarine, and transitional habitats is transferable to similar coastal wastewater schemes across Aotearoa New Zealand.
- Demonstrates the value of investing in 12 months of site-specific baseline data before drawing conclusions about effects – ground-truthing modelled predictions against actual receiving environment conditions produces more defensible assessments than desktop analysis alone.