Evaluation of the conceptual basis of the rational method

It is interpreted in this study that the IUH of the well known rational method corresponds to the time-area concentration curve at the outlet of a symmetrical V-watershed.The appropriateness of this interpolation is verified by simulating a number of hypothetical hydrographs at the outlet of different sizes of area such V-watersheds varying from 0.1km 2 to 1km 2 , using kinematic wave theory of the HEC-HMS model, and proving that for increasing intensity of rainfall over a given watershed area, the kinematic wave hydrograph tends to approach the shape of triangular hydrographs, characteristic of the rational method; Similarly, for a given rate of rainfall and for increasing watershed area, the kinematic wave hydrographs tend to deviate away from the triangular hydrograph shape, thus, establishing the appropriateness of the rational method for application to small urban watershed runoff studies not only for peak flood estimation but also for associated distribution of runoff volume.