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<br />Most of the stations were located near bridges. At every station except <br />the South Platte River and Cache La Poudre River sites, the bridges completely <br />spanned the stream and had no piers and no encroachment on the stream width. <br />Measurements on the South Platte River were made at the midpoint of the spans <br />between piers; these spans were 45.5 feet wide. At the Cache La Poudre River, <br />the bridge pier was 30 feet from the nearest vertical. For each station, <br />details of the relationships between the measuring section location and nearby <br />bridges are given in the Streamflow-gaging Station Description in the Tabu- <br />lated Velocity-Profile Data section at the end of the report. In no instance <br />were bridge piers or abutments felt to affect the flow at the section <br />measured. <br /> <br />In general, selection of the streamflow-gaging stations was based on <br />attaining as large a degree of variation in water-surface slope, depth, and <br />bed material as possible. Sites were selected on streams that have a range of <br />flow resulting from snowmelt so that changes in stage would be small during <br />measurements. The maximum change in stage between velocity observations by <br />the two current meters was 0.03 feet. Usually the stage was constant and no <br />change occurred between observations. There are flow conditions that are not <br />represented by the selected stations. For instance, deep, high-flow, high- <br />gradient streams common in the Pacific Northwestern States were not included. <br />The selected streams do, however, represent a good sampling of the type of <br />streams normally found in Colorado and the Rocky Mountain States. <br /> <br />DATA COLLECTION <br /> <br />Each streamflow-gaging station listed in table 1 was visited at three <br />different times to obtain velocity data for high-, medium-, and low-flow con- <br />ditions. Velocity measurements were recorded only when the variation in gage <br />height from previous visits was 0.5 foot or more. Therefore, two stations, <br />site numbers 8 and 9, have only two sets of measurements. <br /> <br />During each measurement session velocities were measured at three or four <br />verticals in the cross section using both the Price type AA current meter and <br />the Price Model PAA current meter. Verticals were placed at the same loca- <br />. - "" - --- - -Uons-[fi"subsequeiiC me-asuremeiiEs~ - Wf"tliiil-eacli .verfrcar,- -p-o-inrve!ocities" we-u <br />observed at intervals of 0.10 depth beginning at 0.10 depth (10 percent of. <br />total depth measured from the surface) and ending when t~ meter or sounding <br />weight touched the top of the channel bed. An additional observation was made <br />at 0.05 depth in each vertical. These intervals resulted in a significant <br />number of point-velocity observations within 0.5 foot of the water surface or <br />streambed. This is considered too close to the surface or streambed to give <br />reliable results when using the Price type AA current meter; the meter may <br />underregister when placed closer than 0.5 foot to the water surface or stream- <br />bed (Pierce, 1941, p. 3; Buchanan and Somers, 1973, p. 31; Rantz and others, <br />1982, p. 132). Realizing that the point velocities observed close to the <br />water surface or streambed may be unreliable, they are still presented in this <br />report to allow for thorough examination of velocity profiles and mean veloci- <br />ties. Pierce (1941) took a similar approach when he observed point velocities <br />very close to both the water surface and streambed to derive coefficients for <br />determination of mean velocity in shallow-depth streams. <br /> <br />6 <br />