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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 />10 <br /> <br />sub-basin drainage area. <br /> <br />These physical characteristics of <br /> <br />each sub-basin plus two empirical coefficients were used to <br /> <br />develop the unit hydrographs. The empirical coefficients, <br /> <br /> <br />Ct and Cp' are coefficients of time to unit hydrograph peak <br /> <br /> <br />and peak rate of runoff, respectively. These coefficients are <br /> <br /> <br />given in the Drainage Criteria Manual for 60, 40 and 20 percent <br /> <br /> <br />of watershed imperviousness, and it was necessary to interpolate <br /> <br /> <br />to obtain coefficients for the estimated percent imperviousness <br /> <br /> <br />for future land use conditions of the Lakewood Gulch <br /> <br />and McIntyre Gulch basins. These drainage basin characteristics <br /> <br />are shown on Table 2. <br /> <br />The foregoing hydrographic analysis was required to determine <br /> <br /> <br />the volume of flood runoff from excess rainfall depth. In ad- <br /> <br />dition, it was necessary to determine the peak rate of discharge <br /> <br />for a given flood volume. This required that the sub-basin <br /> <br />characteristics, including the two empirical coefficients, and <br /> <br />the rainfall data be used in a computer program to obtain a <br /> <br /> <br />total of 192 hydro graphs for the 24 hydrologic points. <br /> <br />A typical print-out of the numerical data from the computer pro- <br /> <br /> <br />gram developed for the Lakewood Gulch and McIntyre Gulch study <br /> <br /> <br />is shown on Table 3, which follows. The balance of the hydro- <br /> <br /> <br />graph data that was prepared is not included in this report be- <br /> <br /> <br />cause of its bulk. <br />