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University of Canberra
ACT 2601



CLASS Unsaturated Moisture Movement Model U3M-1D can be used for partitioning water balance using Richards' equation in the unsaturated zone for any combination of climate conditions, land-use and soil type. Non-reactive solute balance across the soil profile can also be performed using advective transport. A balance is conducted for each soil material and evaporative, drainage and solute fluxes are simulated over time. Water balance error associated with the numerical approximation is quantified for each soil material. The model uses an adaptable sub-daily time step based on transient climate conditions.

Target user group

The model is designed for use by environmental science professionals including scientists, researchers, State and Federal NRM organisations, Catchment Management Authorities, consultants and students.


U3M-1D is designed for use by professionals with varying levels of expertise in plant water use and recharge modelling. It can be used by expert scientists, modellers and soil physicists to investigate complex issues relating to flow through porous media. Advanced users with measured field data and a sound understanding of soils and plant growth can update parameter files and apply U3M-1D to their own applications. In the absence of field data and parameters, default parameters inbuilt into U3M-1D database can be used.

Example applications

CLASS U3M-1D was implemented on the Little River catchment for all combinations of soil types (14), land-uses (5) and climate zones (4). A total of 90 model runs were carried out. Outputs from these runs were used to produce the spatial surfaces for leakage from the soil profile, plant transpiration, soil evaporation and excess soil moisture for all soil materials. Estimates of saturation excess runoff and leakage from the soil profile were compared with the measured streamflow at the catchment outlet.

Overview of features, advantage and benefits

The main features of CLASS U3M-1D are:
  1. It provides a Windows based user-friendly graphical user interface (GUI).
  2. Richards? equation based hydrology, an established and proven technology for accurate water balance simulations.
  3. Ability to use adaptable sub-daily simulation time steps by sensing transient nature of the atmospheric conditions and attempts to overcome the divergence problems usually associated with solution of the Richards? equation.

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