Introduction

Auckland Council’s Healthy Waters Department is developing an innovative water quality accounting programme to enable effective, transparent and integrated management decisions for waterways.

Healthy Waters monitors rainfall, river levels, overland flow paths and the performance of stormwater management and treatment devices. Data is fed into modelling programmes to inform reporting and decision-making on how to manage waterways for weather events, changing climate, development and land use.

A tailor-made stormwater catchment contaminant model, the Freshwater Management Tool (FWMT), is core to the new accounting programme – combining local data and knowledge with open-source models developed by the United States Environmental Protection Agency.

The FWMT will be integral to Auckland Council’s implementation of NDC requirements and investing in improving water quality outcomes, in rural and urban catchments, for freshwater and coastal waterways – by predicting:

• time series of stormwater generation and runoff
• time series of in-stream concentrations and loads for operationally relevant contaminants – contaminants relevant to catchment management responsibilities specified in the regional stormwater network discharge consent (NDC)
• sources of contaminants. 

The FWMT information allows Healthy Waters to inform:

• design of Healthy Waters asset management plans (AMP) for environmental outcome
• operational network management decisions and compliance reporting by Healthy Waters for performance targets and conditions set out in the NDC
• design of integrated management plans and allocation of funding for environmental outcome (Water Quality Targeted Rate) – including both freshwater and coastal water quality targets downstream from Auckland’s rural and urban catchments.

Freshwater Management Tool model schema for baseline and scenario application.

Programme

The FWMT is part of a digital ecosystem of data, tools and services designed to deliver on core planning and management requirements of the NDC, targeted rate investment and Healthy Waters responsibilities to deliver catchment remediation (“management tool” programme).

The management tool programme includes generation of:

• Datasets – for land use (surface or land cover and use), risk (contaminant generation, connectivity), soils (hydrologic soil groups), streams (erosional risk, vegetation status), contaminants (activity and sub-catchment yields, loads to and delivered through reaches, concentration time-series, grading)
• Typologies – classification systems for rural and urban land, highly erodible land classification and stream classification systems (erosional risk, shading)
• Models – intervention lifecycle cost models (rural, urban), intervention greenhouse gas lifecycle models (rural, urban), intervention opportunity models (feasible footprints, drainage areas), accounting framework (FWMT, Tātaki Wai*) and NDC application tool (NDCalculator)
• Technical documentation – including programme technical papers and reports on core and supporting modelling.

* Tātaki Wai is a FWMT-variant delivered for the Kaipara Moana Remediation group, a partnership between mana whenua (Kaipara Uri – Ngā Maunga Whakahī o Kaipara, Te Rūnanga o Ngāti Whātua, Te Uri o Hau), Auckland Council and Northland Regional Council for informing decision-making on strategic and adaptive management of investment on-farm to remediate the Kaipara moana (harbour).

Management Tool partners and supporters involved in modelling programme.

Principles

The management tool programme (“programme”) has adopted principles throughout, of:

1. Trust and transparency – decision-making on model inputs, configuration, outputs and broader information is publicly available, including clarity of modelling scope and fit for purpose.
2. Best practice (environmental modelling) – programme adheres to USEPA (2009) and MfE (2023) environmental modelling practices.
3. Continual improvement – inviting independent peer review, stakeholder review and versioning as review and validation data becomes available.
4. Fit for operational purpose – information, model design and applications are fit for purpose in managing water quality outcomes.
5. Robustness – model performance meets benchmarks for accuracy, certainty and sensitivity.

Purpose

The overall management tool programme is operational and designed to generate information to manage on a wide array of pollutants, catchment conditions, climate patterns and management scenarios – purposely for managing water quality.

The FWMT is of use in decision-making about development, integrated catchment management, climate resilience and catchment remediation impacts on operational contaminants (sediment, nutrients, metals, faecal bacteria).

The FWMT has been designed for:

• NDC decision-making and reporting requirements of Auckland Council (Healthy Waters, Regulatory Services, network applicants)
• asset management planning forecasting and decision-making requirements of Healthy Waters
• water quality remediation decision-making requirements of Auckland Council (Healthy Waters, mana whenua partnerships, primary sector partnerships, network operator partnerships, developer partnerships).

All other FWMT applications require careful consideration (contact: fwmt@aucklandcouncil.govt.nz).

Staging

Auckland Council is the first government agency to adopt a “management tool” approach in New Zealand – combining continuous, process-based and intervention-optimisable models to underpin baseline, scenario and managed scenario choices for water quality outcome.

The Healthy Waters management tool programme is staged – undertaking internal review, independent peer review and stakeholder extension to identify limitations and prioritising continuous improvement.

Core and supporting models for FWMT Stage 1 are nearing completion.

Development is now commencing to operationalise the management tool programme, via:

1. Communications framework – providing operational services and tools for applying the FWMT to NDC, asset-management and catchment remediation decisions
2. NDCalculator – NDC applicant contaminant generation and treatment calculator based on FWMT outputs.

Validation

Staging allows for ongoing validation, including of intervention, network and waterway changes.

The Healthy Waters management tool programme is developing targeted observational sampling and intervention monitoring programmes – purposely for model validation including targeted at “critical conditions”.

Critical conditions are specific places, times and broader climate conditions associated with management outcomes – process-based, continuous and mountains to sea modelling in the FWMT is ideal for identifying the critical conditions to target sampling and underpin validation with.