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<br />CHAPTER 6 <br />APPROACHES TO FLOOD HYDROLOGY <br /> <br />There are a variety of approacl1es to flood hydrology, This chapter summarizes the <br />approaches, while Chapter 7 describes them in detail, These approaches can be classified <br />into e~her standard or non-standard categories. Standard approaches, as the name <br />implies, are methods commonly \,lsed for flood hydrology estimates, These methods can <br />be considered "tried and somewhat true" methods for flood hydrology estimates, Non- <br />standard methods, though, are not so commonly used techniques or relatively new <br />techniques that have not been \,lsed on a regular basis, but show promise and may be <br />increasingly used in future analysis, <br /> <br />6.1 Standard Approaches. Standard approaches to flood hydrology can be categorized <br />under three methods: <br /> <br />(1) Simplffied methods <br /> <br />(2) Frequency analysis of streamflow data <br /> <br />(3) Rainfall-runoff analysis of storm events <br /> <br />6,1,1 Simolified Method, Simplffied methods may involve use of relatively simple <br />equations such as the rational formula, previously developed regression equations, etc, <br />Depending on time and resources, these methods can be used as stand-alone estimates, <br />or more preferably, should be used for providing an independent check on estimates <br />developed by other, potentially more accurate methods, <br /> <br />Advantaaes <br /> <br />Disadvantaaes <br /> <br />1. Simplic~y, <br /> <br />1, Due to assumptions of homogeneity, <br />method is only for small areas (< 1 mi2), <br /> <br />2, Widely used, particularly for sewer <br />design, <br /> <br />2, Assumes rainfall intens~y is constant <br />during storm duration, <br /> <br />3, Only defines peak discharge, <br /> <br />6.1,2 Freauencv Analvsis of Streamflow Data, Where adequate streamflow data are <br />available, frequency analysis of such data can be perfonned to develop exceedance <br />frequency estimates, Frequency analysis is a method to infer the probability of <br />exceedance of all possible discharge values from observed discharge values, This <br />process is accomplished by selecting a statistical model that describes the distribution of <br />discharges of the parent population, The parameters of the statistical model are estimated <br /> <br />Colorado Flood <br />Hydrology Manual <br /> <br />6.1 <br /> <br />a:w=r <br />