Direct Problem: Infiltration into a one-dimensional soil profile
Possible additional modifications
Inverse Problem: One-step outflow method
The first example represents the direct problem of infiltration into a one-meter deep loamy soil profile. The one-dimensional profile is discretized using 101 nodes. Infiltration is run for one day. Ponded infiltration is initiated with a 1-cm constant pressure head at the soil surface, while free drainage is used at the bottom of the soil profile. The example is divided into three parts: (A) first, only water flow is considered, after which (B) solute transport is added. Several other modifications are suggested in part (C). These include (1) a longer simulation time, (2) considering solute retardation, (3) using a two-layered soil profile, and (4) implementing alternative spatial discretization. Users in this example become familiar with most dialog windows of the main module, and get an introduction into using the external graphical Profile module in which one specifies initial conditions, selects observation nodes, and so on.
The second example considers the inverse solution of a one-step outflow experiment. Data presented by Kool et al. , and used in example 6 of the HYDRUS-1D manual (p. 102), are used in the analysis. Three hydraulic parameters were estimated by numerical inversion of the observed cumulative outflow and the measured water content at a pressure head of -150 cm. Since water exits the soil column across a ceramic plate, the flow problem involves a two-layered system. The profile, consists of a 3.95-cm long soil sample and a 0.57-cm thick ceramic plate, and is discretized using 50 nodes, of which five nodes represent the ceramic plate. Only a few nodes were used for the ceramic plate since the plate remains saturated during the entire experiment, thus causing the flow process in the plate to be linear. Outflow is initiated using a pressure head of -10 m imposed on the lower boundary. Details about this inverse problem are given in the HYDRUS-1D manual.
We believe that by carrying out these two examples, HYDRUS-1D users will obtain the basic skills necessary to solve their own problems. We wish you all the luck and patience needed in this endeavor.