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<br />feet per second (cfs). Due to inadequate channel capacity, this discharge <br />was routed uniformly across the alluvial fan. Because of highly unpredict- <br />able flow direction, all possible flood routes were considered. Three cross <br />sections perpendicular to the major axis of the fan were taken in hydraulic <br />computations for shallow flooding to determine average flood depths. <br />Average depths were computed using the Sribniy formula (Reference 12), a <br />modified Manning's equation, as follows: <br /> <br />v = 1.486 1 H2/3 si/2 <br /> (0.194S 4) <br />V = the mean velocity in feet per second (fps) <br /> -i <br />where <br />H = the average depth in feet <br /> ? <br />S = the slope in feet/feet <br /> <br />The average depths and velocities at the three cross sections as shown on <br />the Floodway Map (Exhibit 2) are tabulated in the following: <br /> <br />Cross Section <br /> <br />1 <br /> <br />:2 <br /> <br />3 <br /> <br />A verage Depth (feet) <br />Mean Velocity (fps) <br /> <br />0.9 <br /> <br />2.0 <br /> <br />2.7 <br /> <br />2.6 <br /> <br />6.8 <br /> <br />10.9 <br /> <br />For Cornet Creek, no flood profiles were developed and the 500-year <br />flooding was not studied. N ei ther was the 10-year flooding studied because <br />the average depth of 100-year flooding was no greater than three feet in this <br />area. <br /> <br />.. <br />~'- <br /> <br />~ <br /> <br />The slope-area method was used for determination of starting water-surface <br />elevations for all other streams studied in detail. Water-surface profiles of <br />selected recurrence intervals were developed using the COE HEC-2 step- <br />backwater computer model (Reference 13). These water-surface profiles <br />were computed to a degree of accuracy of 0.5 foot. The locations of <br />selected cross sections are shown on both the Floodway Map (Exhibit 2) and <br />the water-surface profiles. <br /> <br />Approxima te methods were used to study portions of the San Miguel River, a <br />portion of Leopard Creek, South Fork San Miguel River, and Gurley Ditch. <br />Since there is not any previous study in these areas, an area prone to <br />flooding for the recurrence interval of 100-years was determined by <br />hydraulic calculations, which included estimation of cross sections and <br />discharges to obtain depths of flow. <br /> <br />, <br /> <br />., <br /> <br />The hydraulic analyses for this study are based only on the effects of <br />unobstructed flow. The flood elevations as shown on the profiles (Exhibit 1) <br /> <br />'~ <br /> <br />10 <br />