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<br /> <br />40 <br /> <br /> <br />To determine travel times for each of the channel reaches in the <br />Colorado River basin, knowledge obtained from similar basins and <br />similar studies was applied. Flood flow velocities usually range <br />between 8 and 12 ft/s; therefore, average streambed slopes and <br />channel conveyance characteristics were used to estimate the flow <br />velocities. Generally, the steeper portions of the upper basin had <br />the highest velocities, and the flatter areas around Lake Powell and <br />Lake Mead had the lower values. The channel lengths were divided <br />by the flow velocities to obtain travel times for each reach. <br />Table 3.5 shows the selected t:ravel times for each subbasin. <br /> <br />3.7 DIMENSIONLESS GRAPHS <br /> <br />The dimensionless unit hydrograph is used with the FHAR computer <br />program to calculate the flood hydrograph for each subbasin. The <br />basin above Hoover Dam includes three basic types of terrain - <br />deserts, foothills, and mountains. Data gathered from the field <br />reconnaissance and from analysis of basin features shown on <br />topographic maps were compared with similar data for basins where <br />unit hydrographs had been developed from observed flood hydrographs. <br /> <br />Separate dimensionless graphs were used for each type of topography. <br />The following three dimensionless graphs were used in the study: <br />(1) Southwest Desert for the desert areas, (2) Buckhorn for <br />the foothill areas, and (3) Uinta for the mountainous areas. <br />Tables 3.6, 3.7, and 3.8 show the unitgraph ordinates for the three <br />dimensionless graphs. These dimensionless graphs were derived from <br />analysis of flood events for the Salt River in Arizona, Buckhorn <br />Creek in Colorado, and the Uinta Mountains in Utah. They are <br />considered appropriate for use in this study. <br />