Laserfiche WebLink
<br />collected velocity-profile data in a shallow stream with a coarse-sand and <br />gravel bed. They found that the velocity profiles over dunes and other large <br />roughness elements were nonlogarithmic. This report presents data that was <br />collected to evaluate the magnitude of the problem of computing subsection <br />mean velocity and to determine the hydraulic conditions where the problem <br />exists. <br /> <br />The methods used to collect this velocity-profile data, as well as the <br />data itself, are presented in this report. This completes the first phase of <br />an ongoing research project examining mean velocity determination in high- <br />gradient, shallow-depth streams. The next phase of the project involves <br />evaluation and interpretation of this data and publication of the results. <br />Evaluation will center around existing methods for determining mean velocity <br />by current-meter measurement, their application in high-gradient, shallow- <br />depth streams, needs of additional data collection, and whether new methods <br />for determining mean velocity in these streams are needed. <br /> <br />Problems with computing mean velocity in high-gradient, shallow-depth <br />streams could be widespread. Shallow-depth streams, defined herein as those <br />with depths generally less than 5 feet, are common throughout mountainous <br />areas. High-gradient streams also are not limited to Colorado. About <br />25 percent of the land area in the United States could be classified as steep <br />terrain having water courses that may be described as high-gradient and <br />shallow-depth streams. These land areas include the Western and Eastern <br />Mountain States. <br /> <br />Subsequent analysis of the velocity-profile data presented in this report <br />may enable improvement of discharge-measurement techniques in high-gradient, <br />shallow-depth streams and indicate areas where additional data collection and <br />research is needed. Improved accuracy of velocity and streamflow determina- <br />tion on high-gradient mountain streams would improve the results of hydrologiC <br />studies and hydraulic designs in these areas. Investigations in streamflow, <br />determinations of flood magnitude and frequency, flood-plain studies, and the <br />design of transportation facilities would benefit from improvements in <br />discharge-measurement accuracy. <br /> <br />Approach <br /> <br />Several types of data are required to examine techniques for determining <br />mean velocity in high-gradient, shallow-depth streams. Velocity.profile data <br />are necessary to compute mean velocities and to evaluate existing methods for <br />estimating mean velocity. Water-surface slope data are needed to determine <br />stream gradient and to assess the effect of slope on the velocity profile and <br />subsequent mean velocity determination. Data that adequately dpscribe the <br />characteristics of the streambed are necessary for examination of possible <br />relationships between depth, bed-particle size, and mean velocity. <br /> <br />To assess the contribution of a new development in current meter design, <br />two Price current meters, each equipped with a different type bucket wheel, <br />were used to collect the velocity-profile data. Velocity profiles obtained <br />using the standard Price type AA meter that is commonly used by the U.S. <br />Geological Survey may be compared to those profiles obtained using a prototype <br /> <br />2 <br />