USC model requirements and outputs
Details of model requirements and outputs for the Urban Stormwater Contaminants (USC) model.
USC model requirements
The model requires the following inputs. Estimates of:
- future heavy-metal loads from the land
- future sediment loads and grain sizes from the land
- the natural metal concentrations on catchment soils.
Model parameters include:
- bed-sediment mixing depth in the harbour
- bed-sediment active layer thickness in the harbour.
Patterns of sediment transport and deposition in the harbour, including the way land-derived sediments are discharged and dispersed in the harbour during and following rainstorms, are derived by applying an estuary hydrodynamics/sediment-transport model.
Model initial conditions include:
- present-day grain size distribution of harbour bed sediments
- present-day metal concentrations on harbour bed sediments.
Assumptions need to be made regarding the association of heavy metals with sediment particulate matter. The model is calibrated against annual-average sedimentation rates in the harbour and metal concentrations in harbour bed sediments.
USC model outputs
- predictions of sedimentation in different parts of the estuary, which may be compared and used in an assessment of sediment effects
- predictions of the change in seafloor sediment composition over time (e.g. change of sandy substrate to silt which causes ecological degradation)
- predictions of the accumulation of heavy metals in the surface mixed layer of the seafloor sediments, which may be compared to sediment-quality guidelines to infer associated ecological effects
- an explicit analysis of the links between sediment sources in the catchment and sediment sinks in the estuary, allowing management intervention to be targeted.