The model makes the following assumptions:

  • Contribution of water and any constituents other than salt are calculated at a FU level and accumulated to a sub-catchment level by separate rainfall-runoff and constituent models.
  • Groundwater flows calculated by the plugin are only used for calculating salt fluxes at a link that receives the associated subcatchment fluxes and do not contribute to downstream flows.
  • There is no feedback between the groundwater model and the 1-D Water balance models.
  • All deep drainage becomes recharge at the saturated zone within the time-step.
  • The sub-catchment is parameterised with a single set of hydrogeological values (area weighted average).
  • The groundwater response assumes that aquifers are unconfined.
  • Groundwater discharge can only occur to a stream (not to the land surface).
  • Salt mass balance is conserved in the surface water.


The model is intended to represent salt fluxes at each subcatchment and does not allow for any cross connection between subcatchments.  Groundwater salinity is assumed to be constant within each subcatchment but can vary spatially across subcatchments.  Surface water salinity from functional units are also assumed to be at a constant concentration for a particular functional unit, but can also vary spatially.  Point source salt contributions from dewatering or desalination activities would be input as direct contributions into a stream and therefore do not need to be catered for in this module itself.

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