Realistic Assessment of Maximum Flood Potentials

Abstract

A procedure is proposed which uses probability concepts to achieve a consistent and realistic assessment of the probable maximum flood (PMF) and its use in design or evaluation of high‐hazard dams. A PMF computation involves selection of a sequence of meteorologic and hydrologic events. These include the principal storm, antecedent and/or subsequent storms, time and areal distribution of rainfall, loss rates, and the hydrograph determination. Computed maximum headwater levels used in dam design or evaluation depend on assumed initial reservoir levels, operating conditions, and windwave conditions. A review of present practice shows basic agreement on events or conditions to postulate, but significant differences in their magnitude. These differences produce major variations in the relative magnitude of the computed flood. Further, some events are defined in terms which, when applied in different climatic regions, will result in computed floods of varying relative magnitude. The results of studies conducted by the Tennessee Valley Authority to establish a consistent and realistic standard for PMF determination in the Tennessee Valley region are used to illustrate the proposed procedures.