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<br />A critical need exists to obtain additional data on steep-gradient <br /> <br />streams over a range of flow depths and to provide practical guidelines <br /> <br />for evaluating channel-flow resistance. The investigation described <br /> <br />here was conducted to provide data and improved methods for estimating <br /> <br />the Manning roughness coefficient used to make indirect discharge measure- <br /> <br />ments or estimates of flow depths on steep-gradient streams. This study <br /> <br />aiso provides additional information on other aspects of the hydraul ics <br /> <br />of steep-gradient streams. <br /> <br />COLLECTION OF DATA <br /> <br />Seventy-five current-meter measurements of discharge using a Price <br /> <br />AA meter and appropriate field surveys were made at 21 steep-gradient <br /> <br />natural stream sites in the Rocky Mountains of Colorado for the purpose <br /> <br />of computing channel roughness by the Manning formula and to evaluate <br /> <br />other aspects of the hydraulics of steep-gradient streams. Most of <br /> <br />these sites were at or. near U.S. Geological Survey streamflow-gaging <br /> <br />stations because facil ities for measuring discharge by current meter <br /> <br />/5" <br /> <br />-.c!..- '" <br />"-.V <br />,,~/- <br />~, <br /> <br /> <br />'RL / were available at these sites. A typical steep-gradient stream, Lake <br /> <br />- .... <br />...~ Creek (table 1, site 10) is shown in figure 1; These sites were se- <br /> <br /> <br />lected to represent a wide range of channel type, f1oW'widt~__depth, <br /> <br /> <br />channel slopel.~ roughness, and bed-material size. <br /> <br />The following criteria were used in selecting the sites: <br />t <br />1. Straight channel alinement with little Increase In width in the <br /> <br />downstream direction. This criterion was used because of the uncer- <br /> <br />tainty regarding the magnitude of energy losses attributable to channel <br /> <br />expansion; <br /> <br />2. <br />3. <br />4. <br /> <br />Minimal vegetation on the banks and in the channel; <br />Stable banks and bed having only minor channel irregularities; and <br />Relatively wide stream of simple trapezoidal shape. <br />