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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />shows the relationship of the annual peak discharges to the annual exceedance probability (the <br />percent probability that a flood magnitude would be exceeded in anyone year) obtained from the <br />Log-Pearson probability distribution, The flood frequency curves were created from 328 gauging <br />stations on unregulated streams having at least 10 years of data (USGS, 2000), <br /> <br />The regression analysis developed by the USGS was the ordinary least-squared and the <br />generalized least-squared methods, Flood magnitudes as a function of the drainage basin <br />characteristics were expressed through multiple regression equations, Base 10 logarithmic <br />transformations were used to normalize the data and to obtain linear relationships. The equation <br />that the USGS uses is as follows: <br /> <br />og Q, = logK + a log A + b 10gB + ,..nlogN <br />Where: <br />Q. = The estimated flood magnitude (cfs) <br />K = Regression constant <br />A, B, '" N= Values of drainage basin characteristics <br />a, b, '" n = Regression coefficients <br /> <br />Equation 1 <br /> <br />(USGS, 2000 <br /> <br />The values for each of the variables listed above can be found by refemng to the USGS <br />document, Orchard City is located in the Northwest Region (below 7,500 feet). The <br />corresponding equation for the 100-year peak flow is as follows: <br /> <br />Q=104,7xA624 <br /> <br />Where: <br /> <br />Equation -' <br /> <br />Q = The estimated flood magnitude (cfs) <br />A = Drainage Area (mi2) <br /> <br />(USGS, 2000' <br /> <br />For more information refer to USGS-Analysis of the Magnitude and Frequency of Floods in <br />Colorado (USGS, 2000), <br /> <br />15 <br />