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<br />~,~ .-.--.--. . <br /> <br />c <br /> <br />'.... . <br /> <br />j <br /> <br />, c\- <br /> <br />...:,...' ik..o:2 .)Zl C';all <br /> <br />~'II!'... <br />~ ! ';"1 rAl rA1 W f,Q .,,_ <br /> <br />I " I \ I \ I \ I \ j <br /> <br />Il <br /> <br />Figure 3. End view of weigh pans withdrawn from the trap; <br />bottom doors are completely or partially open. <br /> <br />The numerical designation assigned to each sampler <br />and special sampling arrangement are given in table I. In <br />addition, the table lisls pertinent characteristics of the sam. <br />pIers and indicates the runs in which each sampler was <br />tested. <br /> <br />EXPERIMENTAL PROCEDURE <br /> <br />The different bed materials used during the study <br />were placed in the flume hydraulically by continuously <br />feeding material into the sump, at the intake side of the <br />pump, while the flume was in operation. The sediment was <br />pumped to the upper end of the flume. There, it initially <br />deposited, built up the bed, and then moved downstream as <br /> <br /> <br />Figure 4. Downstream view of sediment trap, weigh-pan sup- <br />port structure, and load cells. <br /> <br /> <br />, <br /> <br />l~ <br /> <br />~_. <br /> <br />Figure 5. Enclosed instrument console with weigh-pan- <br />control, data-acquisition, and master-time systems. Load-cell <br />relays (lower cenler) and demodulators (hidden) controlled <br />opening and closing of weigh.pan doors. Dual. and single- <br />channel strip-chart recorders (upper center and upper right) <br />monitored weigh-pan operation. Magnetic-tape, data- <br />acquisition system (lower right) recorded cumulative time, <br />sampling time, and voltage output from load cells that sup. <br />ported the weigh pans. Master-time system (upper left) gener- <br />ated cumulative and interval times. <br /> <br />the flow velocity and bed slope accommodated transport. <br />Material was added until the depth of sediment at the lower <br />end ofthe study reach was about1.S ft thick. The emplace- <br />ment process ordinarily took about 12 hours. <br />For the fIrst run, and each subsequent run thereafter, <br />water discharge and height of the sharp-crested weir were <br />adjusted to achieve and maintain, in a quasi-equilibrium <br />state, the desired bedload.transport rate and flow depth. The <br />period of adjustment required to reach statiooarity varied <br />from run to run. The duration of the flow-adjustment period <br />(including emplacement of bed material) for all runs and all <br />bed materials is given in table 2. In addition, table 2 lists the <br />duration of the quasi-equilibrium period when the various <br />data included in this report were collected. The periods are <br />expressed in day numbers, which are a count of the number <br /> <br />Tested Bedload Samplers 5 <br />