Abstract:
Subsurface drainage systems are used to control the depth of the water table and to
reduce or prevent soil salinity. Water flow in these systems is described by the Boussinesq
Equation, and the Advection-Dispersion Equation coupled with the Boussinesq Equation
is used to study the solute transport. The objective of this study was to propose a finite
difference solution of the Advection-Dispersion Equation using a lineal radiation
condition in the drains. The equations’ parameters were estimated from a methodology
based on the granulometric curve and inverse problems. The algorithm needs the water
flow values, which were calculated with the Boussinesq Equation, where a fractal
radiation condition and variable drainable porosity were applied. To evaluate the solution
descriptive capacity, a laboratory drainage experiment was used. In the experiment, the
pH, temperature, and electric conductivity of drainage water were measured to find the
salt’s concentration. The salts concentration evolution was reproduced using the finite
difference solution of the Advection-Dispersion Equation, and the dispersivity parameter
was found by inverse modelling. The numerical solution was used to simulate the leaching
of saline soil. The result showed that this solution could be used as a new tool for the
design of agricultural drainage systems, enabling the optimal development of crops
according to their water needs and the degree of tolerance to salinity.
Keywords: Boussinesq Equation, Dispersivity parameter, Finite difference, Fractal radiation
condition, Inverse modeling.
