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<br />3.1 Hydrologic Analyses <br /> <br />Hydrologic analyses were carried out to establish the peak discharge- <br />frequency relationships for each flooding source studied in detail <br />affecting the community. <br /> <br />Since the Limon Watershed Protection project darns were built, <br />the length of record is insufficient to establish a flood history <br />for the modified watershed. Therefore, flooding on similar miscel- <br />laneous watersheds in the area was investigated to determine the <br />runoff potential of small drainages such as the tributaries in <br />this study. Generally speaking, small watersheds produce higher <br />discharges per unit of drainage area than larger watersheds. Regres- <br />sion equations prepared in conjunction with the miscellaneous <br />data suggest that only 1.0 square mile of uncontrolled drainage <br />area would produce a 100-year peak discharge of 1,500 cubic feet <br />per second (cfs). <br /> <br />Peak discharge-frequency data used in this study were derived <br />from regression equations developed by the U.S. Geological Survey <br />in cooperation with the Colorado Department of Highways and Federal <br />Highway Administration (Reference 5). The regression equations <br />used are: <br /> <br />QIO 500 Ae':~ <br />Q25 = 840 Ae' 1.01 <br />QSO = 1,140 Ae 1.07 <br />QIOO = 1,550 Ae <br />Q500 = Based on Extension of Frequency Line <br />Where Q = Discharge (subscript numeral in recurrence interval) <br />A = Contributing Area (square miles) <br /> <br />This procedure established the lower s~gment of a curve relating <br />drainage area to peak discharge. The upper part of the curve <br />is an extension of the lower segment at a slope parallel to a <br />line developed using Colorado Water Conservation Board methodologies <br />(RE,ference6) .----~-- <br /> <br />According to the National Oceanic and Atmospheric Administration, <br />Precipitation - Frequency Atlas for Colorado, the following amounts <br />of rainfall (point values) could be expected for the frequencies <br />shown: <br /> <br /> 6-Hour 24-Hour <br />Recurrence Duration Duration <br />Interval (Inches) (Inches) <br />10 years 2.37 2.90 <br />50 years 3.22 3.95 <br />100 years 3.60 4.41 <br />500 years 4.53 5.55 <br /> <br />8 <br />