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runoff associated with a storm of a given frequency. A number of stoms, each of a different frequency, are used to produce a discharge-frequency curve, This is done by either assuming that the rainfall and runoff frequency relationships are the same or by using an adjustment procedure to relate rainfall and discharge frequency. If no adjustment is used, it is assumed, for example, that the 1 percent frequency storm produces the 1 percent frequency flood flow. e One major weakness of this method is the fact that rainfall of a given frequency does not generally produce a flood of the same frequency, and it is probable that different combinations of rainfall intensities and loss rates can give rise to the same peak discharge. HOwever, when no rainfall or flow data are available, this may be the most acceptable approach, Because of the wide use of this method it will be described in some detail in Chapter 4, 2.5 selection of A Particular Method The particular approach used for the hydrological analysis of a watershed depends on a number of factors (Burnham, 1980). The type of study being performed and the information that is needed from it are important, as well as the amount of time and the personnel available, The characteristics and location of the watershed will influence the method used. Often the experience of the hydrologist and his familiarity with a particular technique will influence him to select a given method over Dthers, even though a less familiar method may give superior results. However, if one assumes comparable expertise, the most important factors in determining the method used for the analysis of an ungaged watershed are the type and amount of data available. The following chapter discusses in detail the effect of data availability and will serve as a guide for establishing the methodology to be used in a given study. e e 10