Runoff Analysis Based on Equivalent Frequency Transfer Function

It is well known that the frequency transfer function (FTF) played as an important role to examine the dynamic behavior of linear system. However, as several studies have focused on linear runoff system, it was necessary to concern non-linearity as well. This study proposed an application of Equivalent Frequency Transfer Function (EFTF) to non-linear runoff models. The EFTF has originally been used among control engineers to solve dynamics of non-linear elements problems for example threshold and saturation elements. It was considered that the obtained EFTF is a lumped function of distributed parameter runoff models over frequency domain. Vector locus, gain and time lag function are proposed in order to investigate the efficiency and effectiveness of EFTF. In addition, this study has pointed out that EFTF can be approximated by means of delay system or approximation method. Simplification of the derivation by applying mathematical techniques is proposed. Finally, our new findings have been applied to available data observed from real catchment basins.