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<br />v <br /> <br />The hydrograph parameters and loss rates rust usually be determined by <br />calibration, from rainfall and flow data. When no data Bre available for a <br />watershed, they rust be estimated by using data from similar watersheds. If <br />the watersheds are hydrologically similar, direct transfer of the data may be <br />done with minor adjustments. More generally, regionalization techniques are <br />used to develop runoff transformation and loss rate parameters. <br /> <br />The methodology for the development of hypothetical storms is presented <br />in detail (pppendix A), with examples of the development of storm rainfall <br />distributions. In many studies, hypothetical rainfall data are the only <br />rainfall data available fDr the study. The approaches presented for storm <br />development use the rainfall intensity-duration-frequency critera developed <br />by the National Weather Service, as presented in the NOAA Atlases (NOAA, <br />1973) and in Technical Paper 40 (U.S. National Weather Service, 1961), COrps <br />of Engineers procedures for configuring the hypothetical storms are used. <br /> <br />Because the methods described in this report rely on the features <br />available in computer program HEC-l, detailed techniques are given for the <br />estimation and calibration of HEC-l model parameters. Included are <br />discussions of the runoff transformation and loss-rate parameters as well as <br />streamflow routing parameters. Typical values of parameters are given for <br />comparison, and the sensitivity of results to parameter estimation errors is <br />discussed. <br /> <br />Three case studies are presented to illustrate the practical application <br />of the material in this report, An example is given for each of three degrees <br />,of data availability: (1) for the case where some discharge-frequency data <br />are available; (2) where some rainfall and streamflow data are available, <br />but where streamflow data are insufficient to determine discharge-frequency <br />curves by statistical analysis; and (3) where no streamflow data exist for <br />the watershed. <br /> <br />The primary objective of this report is to describe how HEC-l can be <br />used to develop peak-discharge-frequency estimates for ungaged areas. The <br />hydrologist can use the material presented here to help choose the <br />appropriate level and detail of a study, basing this decision on the <br />availability of the data, time and funds available, and the accuracy <br /> <br />2 <br /> <br />e <br /> <br />e <br /> <br />. <br /> <br />e <br />