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<br />Elevation-Frequency Curves <br /> <br />Definition, Hydraulic studies and observed streamflow data form the <br /> <br />basis of the elevation-frequency curves, such as those shown in Figure V- <br /> <br />5, which will be required for each reach for existing conditions and for <br /> <br />each plan of local improvement considered ranging from zero damage stage <br /> <br />to the Standard Project Flood, <br /> <br />Use. The elevation-frequency relationships are primarily tools of <br /> <br />economic analysis, Selection of the basic data and derivation of the <br /> <br />statistical relationships expressing flood frequency is a responsibility <br />of both the hydrologist and economist, <br /> <br />Procedure, In previous paragraphs, derivation of elevation- <br /> <br />discharge curves and discharge-frequency curves use is discussed. It is a <br /> <br />simple matter to combine these relationships to establish the elevation <br /> <br />frequency curves, <br /> <br />Elevation,frequency relationships require a combination of hydraulic <br /> <br />and hydrologic information, The hydraulic engineering is mostly <br /> <br />completed earlier, by computing rating curves, During that phase, water <br /> <br />surface elevations are computed for levels of discharge, During this <br /> <br />phase, it is necessary to calibrate frequencies to discharge. <br /> <br />Computation of elevation-frequency curves is a two step process, <br /> <br />which consists of constructing elevation discharge curves from cross <br /> <br />sections and topographic information, and using historic data and modeling <br /> <br />to estimate discharge-frequency relationships, It is then a simple matter <br /> <br />to combine these relationships to establish elevation-frequency curves, <br /> <br />V,l4 <br />