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<br />Large hypothetical floods that represent relatively extreme condi- <br />tions (such as the standard project or probable maximum floods described <br />in Chapters 3 and 4) are needed as a basis of design of projects whose <br />inadequacy would result in major property damage or loss of life. Such <br />extreme hypothetical floods can also be used as reference levels for <br />design floods that are smaller. thus permitting their indirect use in a <br />set of standards and guides for design of projects where potential pro- <br />perty damage and loss of life is not sufficient to warrant design for <br />the full flood magnitude. <br />The need for probable maximum floods that represent the upper <br />feasible limit of anticipated flood magnitudes is of particular impor- <br />tance. These are used to design spillways of major dams where failure <br />would cause a disaster far greater than would be caused by natural <br />flooding. Next in importance is the need for standard project floods <br />that are representative of maximum events that occur within entire <br />regions. These events rarely occur on individual drainage areas. but <br />their occurrence within a region demonstrates that they are a definite <br />threat at any specific location. Lastly. hypothetical floods that have <br />expected probabilities of occurrence at specific locations are needed <br />for economic and other planning and design purposes. This last cate- <br />gory of hypothetical floods must be representative of large ranges of <br />magnitude and of time and area distributions so that evaluations of <br />project effects can be made by simulating project operation using a <br />minimum number of hypothetical floods. <br /> <br />Section 1.03. Application <br /> <br />Hypothetical floods are used primarily to simulate the operation of <br />a project or system of projects in order to verify that facilities and <br />operation rules are adequate. <br />In the case of simple limited channel improvement, floods of all <br />magnitudes are usually reduced in stage. and it is simple to compute the <br /> <br />1-02 <br />