PRELIMINARY EMPIRICAL-MODELS TO PREDICT REDUCTIONS IN TOTAL AND LOW FLOWS RESULTING FROM AFFORESTATION

Mathematical models to predict runoff reductions due to afforestation are presented. The models are intended to aid decision-makers and plan ners who need to evaluate the water requirements of competing land use s at a district or regional scale. Five afforestation catchment experi ments were analysed by the paired catchment method to determine the re ductions in both total (annual) and low flows. The percentage reductio n in flow after afforestation with both eucalypts and pines was determ ined for each post-treatment year relative to the expected flow based on a calibration relationship with an untreated (control) catchment. W e fitted curves to these data points to predict the effects of affores tation under optimal and sub-optimal growing conditions. Eucalypt plan tations were found to depleter both total and low flows sooner and in larger quantities than pine stands.