Since 2016 integrated eReefs catchment and marine modelling has been used to undertake user-specified management scenarios that can provide assessments of how likely proposed catchment load reduction interventions could likely contribute to the achievement of mandated water quality targets. Agreed scenarios (a baseline and 3 or more management interventions) are developed by GBR managers and involve testing varying combinations of nutrient and sediment load reductions on downstream water quality conditions (Chlorophyll as a proxy of nutrient status, suspended sediment concentration) in the GBR lagoon, as well as ecological variables (bottom light, Secchi depth, seagrass cover, zooplankton). Based on these scenarios, catchment loads are firstly predicted from SOURCE and these are subsequently used as input into the regional marine models to predict GBR water column nutrient and sediment concentrations.
What scenarios have been run?
Nine scenarios were completed as part of the scenarios work package and WQ Targets (WQT). The five WQT scenario span dates between 2011 and 2022. The eReefs marine model outputs and scenarios for the 11 years were used to underpin the establishment of Water Quality Targets for Reef Plan 2050. Marine modellers provided expertise and detailed analysis as part of the technical advisory committee December 2023 - September 2024. The model results were approved by the Intergovernmental science panel (ISP).
| Scenarios completed (Report Card 11 period) | Date of model run | Model used | With remote sensing | Number of rivers | Flow |
|---|---|---|---|---|---|
| Baseline | Dec 2010 to Nov 2022 | GBR4 4 km grid |
no | 103 | BoM G2G |
| 25% reduction | Dec 2010 to Nov 2022 | GBR4 4 km grid |
no | 103 | BoM G2G |
| 50% reduction | Dec 2010 to Nov 2022 | GBR4 4 km grid |
no | 103 | BoM G2G |
| 75% reduction | Dec 2010 to Nov 2022 | GBR4 4 km grid |
no | 103 | BoM G2G |
| Preindustrial | |||||
| Multiyear spin up | Dec 2010 to Nov 2022 | GBR4 4 km grid |
no | 103 | BoM G2G |
| No river nutrient of sediment inputs (only flow) | Dec 2010 to Nov 2022 | GBR4 4 km grid |
no | 103 | BoM G2G |
Application of the eReefs marine model scenarios were used to determine marine WQ targets, providing essential data and insights to inform policy and management decisions aimed at protecting the GBR. This includes a major contribution of the eReefs platforms to the development of the Reef 2050 Long-Term Sustainability Plan through the assessment of the Water Quality Targets.
eReefs provides critical Reef modelling scenarios that support and inform the Reef Authority’s resilience-based management and decision-making processes, planning, permitting, monitoring and operations. The eReefs functionality and continued input is essential for planning in relation to climate change mitigation, impact assessment of critical inshore GBR habitats (e.g. seagrass), and associated Reef management strategies. The Great Barrier Reef Marine Monitoring Program provides water quality data for eReefs modelling purposes, which is then reported to the Reef Water Quality Report Card. This reciprocal relationship in the sharing of information helps drive spatial management priority and target review processes that Reef Water Quality programs are reliant upon for management, planning, operations and investment costing purposes.
Dr Kaye Walker, Assistant Director, Science for Management Section, GBR Marine Monitoring Program Leader, Reef Authority