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 Abadia-Goiania-Brazil. A model containing 13 compartments was proposed to explain the water infiltration and the kinetics of the unsaturated zone. To validate the model, tracer injections were carried out at a representative 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 compartment, one component of the evaporation (K4,0) was considered and for the last compartment, one constant of removal for the water table (k13,0). Compartments 1, 2 and 3 were added to the system to consider precipitation effect. The AnaComp program, developed at IPEN, was used to determine the transfer constants ki,j ( from compartment i to compartment j)were i and j range from 0 to 13. In this program the constants ki,j were determined by the nonlinear last squares method, using eigenvalues - eigenvectors routines or alternatively, the fourth order Runge-Kutta routine. In this compartment model, the radioactive tracer was introduced as a single pulse, into the 6th compartment (50 cm depth). This permits to characterize the tracer diffusion processes in the soil studied. The adopted model showed an explanation coefficient f2 equal to 0.78, which is satisfactory for the methodology used. (author)