A CONCEPTUAL-MODEL OF CATCHMENT WATER-BALANCE .1. FORMULATION AND CALIBRATION

A conceptual model of a catchment's annual water balance is developed. The model is based on the sequential separation of annual precipitati on into surface runoff and wetting, and wetting into baseflow and vapo rization. The separation is based on a proportional relation linking t he three variables involved at each step. The generic form of the prop ortional relation is (X - lambda Z(p) - Y)/[(1 - lambda)Z(p)] = Y/(X - lambda Z(p)), in which X is an independent variable, Y is a dependent variable, X is the initial abstraction coefficient, and Z(p) is the p otential value of the difference Z = X - Y. Given a set of model param eters, the method can be used to separate annual precipitation into it s three major components: surface runoff, baseflow, and vaporization. Initial application of the method to literature catchment data provide d encouraging results. The method can be used for estimates of the ann ual water yield throughout the climatic spectrum. The model parameters can be estimated from past experience or calibrated using measured da ta.