A numerical model for practical use based on the 'one-line theory' is presehted to simulate shoreline changes due to construction of coastal structures. The model contains the part to calculate wave deformation for estimates of wave energy flux at the breaking point. The algorithm for wave deformation is based on the wave-ray method, and takes the following effects into account;i.e., wave refraction. shoaling, reflection and diffraction.
　Firstly, in this paper, the contents of the present model are out-lines. Then, to examine the characteristics of this model, the effects of the assumptions and
parameters contained in the model are clarified through the calcuations of shoreline change for simplified cases. Further, some descriptions on numerical instabilities and time scale of shoreline change are also presented. In particular, it is shown theoretically that the time scale is proportional to the equare of the alongshore length of the beach concerned.
　Finally, as the guides for the practical application of this model, several comments are made on the required data and the determination of the parameters used in the model, with the presentation of two typical examples of the application of this model.