Modelling and monitoring

Modelling program

Monitored pollutant loads leaving catchments vary significantly from year to year, mainly due to differences in annual rainfall and run-off. Therefore, catchment modelling is used to estimate the long-term annual pollutant load reductions due to the adoption of improved land management practices. This removes the impact of factors such as climate variability.

Research suggests time lags to monitor the improvements from land management practice change could range from years for pesticides, up to decades for nutrients and sediments, due to the high level of climate variability.

The Great Barrier Reef Catchment Modelling Program estimates average annual loads of key pollutants (sediment and nutrients) for each of the 35 catchments draining to the Great Barrier Reef as part of the Paddock to Reef program. It reports on baseline levels and the change in loads for each subsequent year due to adoption of improved land management practices. This assesses progress towards the Reef water quality targets with the latest results available in Report Card 2019.

For more information about the modelling, refer to the Methods to create report card .

Modelling can also be used to assess the level of adoption needed to achieve the targets. The Modelling improved land management practices: Management scenario modelling of innovative (lowest risk) to minimum standard (moderate risk) practices report estimates the required increase in improved management practice adoption to meet the water quality targets.

An independent review of the modelling program was undertaken in 2019.

Catchment loads modelling program technical reports:

Regional technical reports were produced covering 2009–2013:

Monitoring program

The Great Barrier Reef Catchment Monitoring Program tracks long-term trends in water quality entering the Great Barrier Reef lagoon from adjacent catchments as part of the Paddock to Reef program. The monitoring data is used to validate the catchment water quality models that track progress towards the Reef targets.

This involves monitoring 43 sites in 20 key catchments for sediment and nutrients and a further 19 sites for pesticides. Samples are collected on a monthly basis during ambient (low flow, dry season) conditions and every few hours to daily during high flow events in the wet season.

The concentrations of contaminants are determined and the volume of water flowing in the rivers is then used to determine the total amount of each contaminant (i.e. the load) that flows past the sampling sites.

For more information about how the loads are monitored, refer to the Methods to create report card .

You can also access more information about the methods used to estimate the pesticide risk metric, pesticide risk baseline and the pesticide condition results.

The catchment loads monitoring results are reported through an interactive Story Map:

The loads for all measured contaminants were previously released in an annual technical report: