PRACTICAL DETERMINATION OF HYPOTHETICAL FLOODS

A comprehensive procedure for simultaneouslyfrelating storm rainfalls of a range of frequencies to runoff hydrographs of the same frequencies is suggested. Hypothetical storm rainfall is developed from published rainfall frequency data and then related directly to runoff peaks and volumes of corresponding frequencies obtained from recorded runoff. The vexing questions of what rainfall patterns to use to define a storm of a specified frequency and what ground conditions to use for converting the rain to runoff of the same frequency are answered in the model calibration process. Using the same criteria in application as in calibration eliminates some major uncertainties. The primary reason for relating rainfall to runoff is to compute flood hydrographs for conditions and locations other than those for which adequate runoff records are available. Once sound relationships are developed where good runoff data are available, such relationships can be used to assess flood potential for other basin conditions and management plans, as well as for other locations. © ASCE.