Application of the compartmental analysis theory to the studies of the kinetics of the rainfall infiltration in the unsaturated zone in Abadia de Goias

The compartmental analysis was used for evaluation of kinetic parameters of the rainfall infiltration and determination of ground water recharge in Ab adia de Goias - Goiania-Brazil. A model containing 13 compartments was prop osed to explain the water infiltration and the kinetics of the unsaturaded zone. To validate the model, tracer injections were carried out at a repres entative site of the region, at a depth of 50 cm, below the root zone. Soil samples were taken 4, 9 and 12 months after the injection. In the first co mpartment, one component of evaporation (k(4,0)) was considered and for the last compartment, one constant of removal for the water table (k(13,0)) Co mpartments 1, 2 and 3 were added to the system to consider precipitation ef fect. The AnaComp program, developed at IPEN, was used to determine the tra nsfer constants k(i,j) (from compartment i to compartment j) where i and j range from 0 to 13. In this program the constants k(i,j) were determined by the nonlinear least squares method, using eigenvalues - eingenvectors rout ines or alternatively, the fourth order Runge-Kutta routine. In this compar tment model, the radioactive tracer was introduced as a single pulse, into the 6th compartment (50 cm deep). This permits to characterize the tracer d iffusion processes in the soil studied. The adopted model showed an explana tion coefficient r(2) equal to 0.78, which is satisfactory for the methodol ogy used.