Main Processes

In the Main Processes dialog window, users specify the processes to be simulated, i.e., Water Flow, Solute Transport, Heat Transport, and/or Root Water Uptake.

The Dual-Permeability Module can be selected as an alternative description for water flow.

Furrow Module        The  Furrow module can be selected to simulate the coupled surface-subsurface flow and transport processes occurring during furrow irrigation and fertigation [Brunetti et al., 2018] The hybrid Finite Volume – Finite Element (FV-FE) model combines a one-dimensional description of water flow and solute transport in an open channel with a two-dimensional description of water flow and solute transport in a subsurface soil domain. The additional input parameters required by the Furrow module are specified in the "Furrow Parameters" dialog window..

When Solute Transport is selected, users can choose from multiple modules of different complexity. The Standard Solute Transport module is described in detail in the HYDRUS Technical Manual. This module allows consideration of individual solutes (one or several) that are either independent, or subject to sequential (or consecutive) first-order decay reactions.

Other solute transport modules (briefly described below) can consider multiple solute components that can mutually interact.

Wetland Module        Check this box if the Wetland module is to be used. The Wetland Module (for two-dimensional problems only) was developed to model biochemical transformation and degradation processes in subsurface flow constructed wetlands. In the wetland module two biokinetic model formulations can be chosen: (1) the biokinetic model as described in CW2D [Langergraber and Šimunek, 2005, 2006, 2011] and (2) the CWM1 (Constructed Wetland Model #1) biokinetic model [Langergraber et al., 2009]. In CW2D aerobic and anoxic transformation and degradation processes for organic matter, nitrogen and phosphorus are described, whereas in CWM1 aerobic, anoxic and anaerobic processes for organic matter, nitrogen and sulphur.

Unsatchem Module        The Major Ion Chemistry Module [UNSATCHEM; Šimůnek and Suarez, 1994] can be used instead of the standard solute transport module. Detailed description of the UNSATCHEM Module is given in the UNSATCHEM user manual [Šimůnek et al., 2012c]. More detailed description of concepts used in the UNSATCHEM module is provided in the HYDRUS-1D manual [Šimůnek et al., 2008], which provides  all relevant information about the one-dimensional version of this module.

C-Ride Module        The C-Ride module simulates two-dimensional variably-saturated water flow, colloid transport, and colloid-facilitated solute transport in porous media. The module accounts for transient variably-saturated water flow, and for both colloid and solute movement due to advection, diffusion, and dispersion, as well as for solute movement facilitated by colloid transport. Detailed description of the C-Ride Module is given in the C-Ride user manual [Šimůnek et al., 2012b].

HP2 Module        The HP2 module is the result of coupling Hydrus (its two-dimensional part) with the PHREEQC geochemical code [Parkhurst and Appelo, 1999], and corresponds to a similar one-dimensional module HP1 [Jacques and Šimůnek, 2005, 2010; Jacques et al., 2006, 2008]. HP2 has, apart from the dimensionality (2D), the same capabilities as HP1. HP2 contains modules simulating (1) transient water flow, (2) the transport of multiple components, (3) mixed equilibrium/kinetic biogeochemical reactions, and (4) heat transport in two-dimensional variably-saturated porous media (soils). Detailed description of the HP2 Module is given in the HP2 user manual [Šimůnek et al., 2012a].

The program automatically considers transient water flow when the “Water Flow” option is selected. Otherwise the code tries to calculate steady-state flow from the specified initial and boundary conditions. The success of such calculations depends on the complexity and/or nonlinearity of the problem. If unsuccessful, then a model run with constant boundary conditions and long simulation time may be required.

If the solute transport, heat transport or root water uptake options originally considered in an existing project are switched off by the user, the program issues a warning that all data related to these processes will be lost. If this loss is undesirable we recommend that users first copy the input data of the current project to a new project before switching off the solute transport, heat transport and/or root water uptake options.

For two-dimensional problems a user can also select if a Direct or Inverse Problem (Inverse Solution?) is to be solved. Inverse problems involve the estimation of selected parameters from available experimental data.

A new add-on module Slope Classic was included in Version 2.04. The Slope Classic module is intended to be used mainly for stability checks of embankments, dams, earth cuts and anchored sheeting structures (see Section 3.23 of the User Manual).

A new add-on module Slope Cube was included in Version 2.05. Details about the Slope Cube module are given in its own manual.

Slope Classic Module        The Slope Classic add-on module uses results obtained by HYDRUS (i.e., relative saturations and water fluxes) for subsequent slope-stability analyses. The module is intended mainly for stability tests of embankments, dams, earth cuts, and anchored sheeting structures. The influence of water is modeled using the distribution of pore pressure, which is imported automatically from HYDRUS runs into the SLOPE module at specified times, each of which can be analyzed separately. The slip surface in the SLOPE module is considered to be circular, and is evaluated using the Bishop, Fellenius/Petterson, Morgenstern-Price or Spencer method [Lu and Godt, 2013]. More details can be found in the user manual of this module. See Section 3.23.

Slope Cube Module        While the Slope Classic module (added in version 2.04) is based on classical engineering soil mechanics theories and uses the effective stress approach only for saturated conditions, the new add-on module "Slope Cube" (Slope Stress and Stability) was developed to provide a unified effective stress approach for both saturated and unsaturated conditions [Lu et al., 2010]. The module is intended to predict spatially and temporally infiltration-induced landslide initiation and to carry out slope stability analyses under variably-saturated soil conditions. Transient moisture and pressure head fields are directly obtained from the HYDRUS-2D model, and subsequently used to compute the effective stress field of hillslopes [Lu and Godt, 2013]. Furthermore, instead of the methodology of one-slope for one factor safety in the classical slope stability analysis, the SLOPE Cube module computes fields of the factor of safety in the entire domain within hillslopes [Lu et al., 2012], thus allowing identification of the development of potential failure surface zones or surfaces.