The Module Soil in MOHID solves
the Richards equation for Saturated and Unsaturated porous media.
This module is used for water flow in porous media. In the present,
the hydraulic properties are described using Van Genuchten function.
However the model is prepared, if needed, to include any model that
describes the relation between water content and pressure head and
the relation of conductivity and pressure head.
The Module Soil of MOHID simulates
water flow in soil. The forcing functions are evaporation and
precipitation, with the possibility of formation of a water layer (in
future programming this water layer will be drained due to run-off).
Other simple forcing conditions, also implemented, are: flux and water
content on the surface.
Initialisation and forcing can be
specified in the domain with boxes. This means that it is possible to
simulate the spatial heterogeneity of the system. This is essential to
simulate soil because normally their hydraulic properties change with
depth. MOHID can simulate in
1D, 2D or 3D. This allows the study of complex field experiments, like
the one presented below. In this experiment part of the soil was covered
(with a plastic liner), which implied that evaporation only happened
around the liner. However this experiment also shown that, under the
plastic liner (where there was no evaporation), the horizontal gradient
was enough to lower the water content.
Simulation of water flow in very dry
soils has numerical problems due to the existence of high gradients.
This model is particularly suitable for calculations in very dry soils
because: (i) is mass conservative (it uses finite difference); (ii) it
can optionally solve the Richards equation explicitly or implicitly
(Thomas algorithm); (iii) the type of convergence method is optional.
In the present it is been developed
the module, which will allow the transport of properties in the soil.
This transport will be made in accordance with the Convection-Dispersion
Equation (similar to Advection-Diffusion Equation).