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<br />,'; <br /> <br />Sediment <br /> <br />Two types of sediment were used in the 2-ft 'tilting flume. The <br /> <br /> <br />first was silica sand, having a median fall diameter (d50) of 0.28 mm, <br /> <br />and specific gravity of 2.65. Movement of particles for this sediment <br /> <br />began at an average velocity of about 0.90 ft per second. <br /> <br />The second type used was light-weight material obtained from the <br /> <br />Great Western aggregate plant in Laramie, V1yoming. Commercially the <br /> <br />aggregate is used for concrete. The median fall diameter for this <br /> <br />material was 0.37 mm with specific gravity of 1. 78. Al though detailed <br /> <br />studies were not attempted to establish the velocity at which particle <br /> <br />movement began, the observed velocity for incipient movement was much <br /> <br />lower than for the first sedi~ent used; at about 0.4 to 0.5 it per second. <br /> <br />Weir Models <br /> <br />There were several variations in shape of broad crested weirs <br /> <br />tested. The dimensions of these weirs are given in Figs. 2-8; <br /> <br />Weir A - The broad crested weir of Fig. 2 had the basic shape <br /> <br />recommended in the Field Investigation Report. The upstream face was <br /> <br />sloped at 2:1 and the downstream face at 3:1. The height of 16.2 inches <br /> <br />was based on sand depth of 9 inches in the flume and crest height of <br /> <br />7.2 inches (3 ft prototype) above the average channel bed. The crest of <br /> <br />the weir was 2.0 ft. <br /> <br />, .. t- _ ;"", <br />\,:. ~.I 1. ~~ ~.... ... <br /> <br />-7- <br />