The use of unit‐Source watershed data for runoff prediction

The conceptual model upon which studies of hydrologic relations between unit‐source and complex watersheds are based is discussed. Comparisons of measured storm runoff from two complex watersheds with that predicted by combining storm runoff of representative unit‐source watersheds in accordance with the conceptual model revealed that the measured values were different from those predicted. Within the framework of the present model, unit‐source watersheds cannot be used to predict the effects of land use changes on complex watersheds. If the unit‐source concept is to find effective application, an improved model must be developed. Three phenomena that seem necessary in a more realistic model are discussed: (1) Interflow, (2) partial area runoff production, and (3) the influence upon downslope runoff production of runoff from upper slopes.