PHYSICALLY BASED FLOOD FEATURES AND FREQUENCIES

Hydrographs and flood-frequency distributions are often required for hydrologic and hydraulic analysis of small ungauged basins. Due to the lack of runoff data, a numerical model to relate rainfall with runoff cannot be used without appropriate calibration. Thus, it would be extremely useful to obtain critical elements of hydrograph and flood-peak distribution for small ungauged basins from rainfall and basin characteristics. In this study, simple expressions are developed to express the time of concentration, time to peak, and peak flows as functions of basin and storm characteristics for small basins, based on results obtained from a specially derived kinematic wave rainfall-runoff model. Following the approach presented in several classic papers by Eagleson, the distribution of flood peaks is derived. These flood-peak distributions are based on the assumptions that the arrival of storm events can be modeled by a Poisson process, and that the relationship (as derived from this study) expressing peak flow as a function of rainfall and basin characteristics is valid. The derived flood-frequency distributions are applied to several contrived basins with various storm and basin characteristics. The sensitivities of these parameters on flood-frequency distribution are also investigated. © ASCE.