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<br />Peak discharge-drainage area relationships for Clear Creek and <br />South Clear Creek are shown in Table 1. <br /> <br />TABLE 1 - SUMMARY OF DISCHARGES <br /> <br />FLOODING SOURCE <br />AND LOCATION <br /> <br />DRAINAGE AREA <br />(SQ MILES) <br /> <br />PEAK DISCHARGE (cubic feet per second) <br />10-YEAR 50-YEAR 100-YEAR SOO-YEAR <br /> <br />Clear Creek <br />At northern corporate <br />limit of Georgetown 81.0 <br /> <br />980 <br /> <br />1330 <br /> <br />1480 <br /> <br />1810 <br /> <br />Clear Creek <br />Upstream from South <br />Clear Creek <br /> <br />47.5 <br /> <br />600 <br /> <br />830 <br /> <br />910 <br /> <br />1110 <br /> <br />South Clear Creek <br />At mouth <br /> <br />30.7 <br /> <br />420 <br /> <br />580 <br /> <br />640 <br /> <br />790 <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />riverine sources studied were carried out to provide estimates of <br />the elevations of floods of the selected recurrence intervals. <br /> <br />An analysis of the hydraulic characteristics of Clear Creek and <br />South Clear Creek was performed to determine water-surface <br />elevations for the 10-year and 100-year floods on each stream. <br />Cross see tion data were taken from a 2-foot contour map of the <br />Town of Georgetown (Reference 5). Building areas were "blocked <br />outll of the cross sections to determine the effective flow through <br />the floodplain. This cross section data became input data for the <br />U. S. Army Corps of Engineers (COE) HEC-2 step-backwater computer <br />program. Bridge elevations and sizes of openings were surveyed <br />and measured in the field by Black and Veatch Consulting Engineers <br />(B&V). The data were reviewed and field checked by the CWCB. <br /> <br />A comparison of bridge cross section elevations surveyed by B&V <br />with those obtained from the 2-foot contour map led to the <br />conclusion that there was a significant problem with the datum of <br />one of the two sources. Further study of the problem was thus <br />undertaken. Two other sources of elevation data were used in this <br />analysis: a I-foot contour map of the vicinity of Georgetown Lake <br />(Reference 6), and two field surveys of selected cross sections <br />along Clear Creek performed in May 1979 by Hayes and Soucie. A <br />total of 60 points from the three described sources were compared <br />with the corresponding points on the 2-foot contour map. From <br /> <br />6 <br />