Abstract: According to a general theory of conceptual watershed geomorphy concentration model, using the conceptual element of diffusion analogy reach to simulate the concentration action of each ordering unit channel, this paper developes a diffusion analogy type watershed geomorphy concentration model in which the parameters are flood wave velocity and diffusion coefficient. The instantaneous unit hydrograph (iuh) of three order basin is derived, and the nature of the iuh is analysied. The author discusses the methods of moment and interior penalty functon (ipf) which are used to obtain the parameters of the proposed model. The model is tested in Nanyan catchment and the result shows that the model has a rational structure and an accuracy when the ipf method is used.

Key words: diffusion, analogy, watershed concentration, geomorphy, interior penalty functon method