Estimating sediment loads in Great Barrier Reef catchments: the balance between modelling and monitoring

In catchments adjacent to the Great Barrier Reef World Heritage Area, there is growing concern that sediments and nutrients being exported from the land are having a detrimental effect on coral reef communities. Monitoring programs have been initiated in the Burdekin catchment to determine rates of sediment runoff and to provide important base line data against which to evaluate any future effect of land management changes. Due to the spatial limitations and high cost of field monitoring, modelling has also been carried out to determine the current sediment loads across the Burdekin catchment. This paper presents a comparison of some of the measured and modelled sediment load data. The data suggest that there is good agreement between end of sub-catchment measured and modelled sediment loads. However, more detailed process based field monitoring has highlighted that the model does not necessarily accurately represent the different erosion processes contributing to the end of catchment loads, at least during drought conditions. The field data also suggest that there is a significant delay between changes in land condition and end of catchment sediment loads, and further work is needed to quantify the temporal lag between land management change and water quality response.