US EPA

7872929 

Journal Article 

Incorporating variable cover in erosion algorithms for grazing lands within catchment scale water quality models 

Searle, RD; Ellis, RJ 

2009 

3542-3548 

WOS:000290045003084 

There is currently a high degree of interest in sediment loads being supplied to the Great Barrier Reef (GBR) lagoon. While monitoring provides an effective tool for quantifying the actual load of sediment being supplied to the reef, it is often difficult, without an exceptionally detailed monitoring network, to determine from this data where and why sediment is being produced. Also given the long duration of measurement required to ascertain trends in a highly dynamic system, and the vast areas needing to be assessed, it is generally impractical to quantify these impacts directly through monitoring. Broad scale catchment modelling has a role to play in helping land managers assess the temporal and spatial aspects of sediment generation. In Australia there are currently two modelling paradigms typically applied to investigate broad scale catchment sediment generation. These are the USLE based steady state or long term average assessment (e.g. SedNet) style of model, and the temporal constant concentration (e.g. WaterCAST) models. While both of these approaches have their benefits in helping us understand catchment processes, they are limited in their ability to improve our understanding of the interactions of temporal and spatially variable sediment generation processes. With recent developments in the remote sensing of ground cover and the development of the WaterCast catchment modelling framework, an opportunity to incorporate both temporally and spatially variable estimates of cover into broad scale catchment water quality modelling has arisen. This study reports the development of techniques to utilise the remotely sensed Bare Ground Index, a satellite estimate of ground cover, into the daily timestep WaterCast Modelling framework to improve our representation of sediment generation dynamics within catchments. Both the highly calibrated EMC/DWC base model and the newly developed RUSLE Variable Cover model provide sound temporal estimates of sediment load generated within the catchment. The fixed EMC/DWC modelled sediment concentrations do not closely match observations, while the RUSLE Variable Cover model estimates do a better job at predicting concentrations. The ability to incorporate spatially and temporally variable cover estimates for sediment generation into WaterCast is a useful advance in catchment water quality modelling. The variable cover estimates allow us to more realistically determine sediment generation hot spots within the catchment and hence gain a much better understanding of the management required in specific areas of the catchment. 

Water quality; remote sensing; USLE; WaterCast; sediment generation