ABSTRACT
The empirical models, on the other hand, relate input to the output assuming a very general relationship between the input and the output with little or no attempt to identify the physical processes involved. The empirical models are also referred to as system-theoretical models (Lettermann, 1 99 1 ) . Most of the unit hydrograph methods originally introduced by Sherman ( 1 932) are widely used examples of empirical models. Although the derivation of this type of models is purely empirical the selection of the input-output parameters are, by and large, dictated by some physical understanding of the processes.
