Richards equation feasibility in predicting flow in unsaturated solid waste at a semi-arid tropical landfill

Abstract

The validity of a model that calculates one-dimension, one-phase, vertical transient water flow through unsaturated Municipal Solid Waste (MSW) was verified by comparing the simulated results against data obtained in a new field experiment. The experimental data consisted of absolute moisture profiles that changed over time from columns packed with real solid wastes, measured by a Neutron Probe, and subjected to an artificial intense rain event. The artificial rain tried to simulate the precipitation intensity present in a semi-arid tropical region, The results showed that in order to adjust to the experimental curves, the field capacity had to be increased during the simu- lation by changing the characteristic equation empirical parameter acf. It was also found that, when used in the simulation process, the measured hydraulic conductivity at saturation (K s = 1.71 × 10 –04 cm/sec) was not able to represent the experimental unsaturated flow. Only by attributing large values to K s (such as 10,000 cm/hr), was it found a good fit to the experimental curves. Although it was possible to mimic them using the Richards equation, it is evident that the conceptual model used is not a physically sound representation of the observed phenomenon.