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<br />STREAMFLOW MEASUREMENTS <br />The following five methods may be used to measure surface-water flow, depending on the <br />hydraulic conditions and the accuracy required: <br />BUCKET AND STOPWATCH METHOD <br />This method will be used where channel geometry and flow rates allow ahand-held bucket to <br />capture the entire streamflow over a time period of at least 5 seconds (approximately < 100 <br />gpm). The elapsed time to displace a known volume is recorded. This procedure should be <br />repeated three times and the average flow computed. Measurements will be recorded in a field <br />logbook. Measurement accuracy is relatively high. The method requires a graduated bucket <br />and stopwatch. <br />PORTABLE FLUME <br />If the geometry of the channel is adequate, the flow is less than about 1.0 cubic feet per second <br />and/or the depth is less than about 0.3 feet, a portable cut-throat flume may be installed in the <br />channel to measure the flow. The flume will be leveled and the flow channelized through the <br />throat of the flume. The water level on the flume staff will be recorded and the standazd <br />rating supplied with the flume will be used to calculate the dischazge. Measurements will be <br />recorded in a field logbook. <br />SURFACE OR FLOATING STICK METHOD <br />This method will be used in open channels to approximate streamflow where the bucket and <br />stopwatch, portable flume, and wading and suspension methods are not feasible. Under most <br />conditions, the measurement error can be expected to range from about 10 to 25 percent <br />(USGS, 1977). A representative section of channel with relatively uniform flow is chosen. <br />Water depth is measured at several points across the channel in addition to the channel width. <br />The cross-sectional area is computed and an appropriate length of channel measured. A <br />floating object (stick, float, etc.) is placed in the center of the channel and the elapsed travel <br />time over a measured distance recorded. This should be repeated five times and an average <br />travel time computed. Measurements will be recorded in a field logbook. The average <br />velocity (distance time) is multiplied by a constant of 0.85 to convert surface velocity to a <br />mean velocity in the vertical (iTSGS, 1977). Finally, discharge is computed using the equation <br />Q = AV, where Q =discharge in cubic feet per second, A =cross sectional area in square <br />feet, and V =velocity in feet per second. <br />WADING METHOD <br />