Biophysical Risk Mapping
The Bay of Plenty Regional Council (BOPRC) sought A2E for advice to develop a contaminant risk mapping framework to support their land managers in targeted conversations with landowners on potential mitigation opportunities. The biophysical risk maps (i.e., E. coli, Nitrogen, Phosphorous and Sediment) will help landowners make decisions to help meet catchment targets, including sediment reduction, mahinga kai, wetland management, and Te Mana o te Wai.
Through A2E, WSP Primary Industries team members, Dr Glen Treweek, Jessica Hall, Dr Istvan Hajdu and Aimee Dawson provided their expertise to develop risk models in collaboration with the BOPRC team.
As the freshwater farm plan regulations are being rolled out across New Zealand, the landowners who meet certain criteria are required to develop a risk profile of their farm regarding freshwater quality. Identifying the risks a farming operation has to freshwater is the first step in the freshwater farm planning process. Risk identification leads to appropriate land management and the implementation of risk mitigations. Farm specific risk is the combination of ‘inherent biophysical risks’ and ‘management risks’.
The experts delivered three key outputs:
A spatially explicit, GIS-based mapping tool developed in the form of an ESRI ArcGIS toolbox
Methodology documentation with the intention to create an easily replicable method. BOPRC will be able to refer to this when rolling the mapping out in other catchments and by users in other regions that may develop similar information in future will also be able to refer to this document. Furthermore, it will help to understand the context of inherent risk mapping and its purpose along with its limitations.
A series of contaminant risk maps for two catchments in the Bay of Plenty (Waihī Estuary primary catchment and the Nukuhou which is a secondary catchment within the Ōhiwa catchment). These maps were created with the intention of creating an easily replicable method that could be used in other catchments in the Bay of Plenty region and potentially across Aotearoa, New Zealand.
WSP and BOPRC identified the following:
Mapping inherent biophysical risks to freshwater involved integrating environmental variables like elevation, slope, soil properties, land cover, rainfall, waterways, and flow paths to assess their combined impact.
Field validation at pre-selected sites gathered feedback from land managers to refine the maps and better capture the landscape’s risk profile. While preliminary maps were accurate, the validation workshop offered crucial insights that enhanced mapping quality (Note: these risk maps are not contaminant load models and should not be interpreted as such).
The project was successfully delivered, with BOPRC now using the models to create contaminant risk maps for all other catchments, soon to be available online. These maps will aid decision-making and facilitate discussions with landowners about mitigation opportunities. BOPRC has also released factsheets to help users interpret the contaminant risk maps and understand their limitations.
This project provides much-needed farm-scale spatial guidance for freshwater farm plan development in future. As the risk modelling tool will be publicly available, other regional councils will have access to the tool to create risk maps. Landowners are also able to add this to their base layers for enhanced identification of inherent biophysical risks.
