Overview of WatBal

The WatBal model performs a daily water balance on piggery effluent treatment and storage systems.

In summary, the WatBal model includes provisions for modelling additions to the effluent stream from piggery manure, waste feed, fresh and recycled flushing and hosing water used for shed wash-down, any runoff from shed rooves or outdoor production areas, drinking water wastage, and rainfall falling onto pond surfaces.  Effluent system extractions incorporated in the model include evaporation from pond surfaces, and use of recycled effluent for shed cleaning and application (irrigation) onto land growing crop and/or pasture.  A daily water balance for the soil in the effluent application area is used to trigger effluent application to land when the soil water deficit reaches a selected value.  This soil water balance allows selection of a range of typical crop/pasture species growing on a selection of different textured soil types in the application area.  The model uses historical daily climatic data which is conveniently downloaded from the SILO climate data website (https://www.longpaddock.qld.gov.au/silo/).  An interactive map is provided to assist the user in selecting the most representative climate data recording station located near the piggery site.  The model accommodates analysis periods commencing from 1900 up until the day prior to the analysis.

Other features of the model include:

  • Ability to model a single effluent treatment and storage pond and two ponds operating in series (primary anaerobic treatment pond + effluent storage pond).
  • Several common effluent pre-treatment/solids separation options.
  • A range of primary anaerobic pond design options, including conventional large ponds (ANSI/ASAE, 2011), heavily loaded anaerobic (HLA) ponds (Skerman et al., 2008) and covered anaerobic ponds (CAPs).
  • Provision for shandying (diluting) effluent by mixing with clean water prior to application to land.
  • Various effluent irrigation management options, including variable soil moisture trigger levels and maximum daily application volumes.