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<br /> <br />DRAFT <br /> <br />model unit sediment discharge rate (q,') will be too great for Grain Reynolds numbers ranging <br />between 5 and 100. Therefore, the model sediment size fractions should be adjusted to properly <br />simulate sediment transport in this range. <br /> <br />A diagram of settling velocity (w) of sand and silt particles (fig. 7) illustrates that small particles <br />(less than 1 mm in diameter) settle at slower velocities as the particles become smaller. In order <br />to adjust the sediment discharge rate in the model, particles less than 1 millimeter in diameter are <br />increased in size until the settling velocity is corrected to the proper velocity consistent with Froude <br />scaling. Particles larger than 1 millimeter settle as a function of the diameter (d) to the 1/2 power. <br />consistent with Froude scaling. When the model grain sizes are adjusted for settling velocity, the <br />value of l' decreases while the value of R' increases bringing the model value of q,' closer to the <br />same value as the prototype. The grain size distribution of bedload in the South Platte at Oxford <br />Avenue was simulated in the model. Figure 8 shows the prototype and model grain size <br />distributions. The model grain sizes were adjusted as described above to compensate for Reynolds <br />number effects. <br /> <br />MODEL RESULTS AND ANALYSIS <br /> <br />The main areas of the model study were (1) model calibration, (2) boating conditions, (3) sediment <br />studies, and (4) floodflow conditions. These and other areas are discussed in the following sections. <br /> <br />Model Calibration <br /> <br />The model was calibrated to accurately measure discharge. Flow entering the model was measured <br />with a Venturi orifice meter. Orifice plates ranging in size from 1-3/8 to 4-3/8 inches were used. <br />A mercury manometer indicated the differential across the plates. The accuracy of the orifice <br />meter and manometer was also checked with a strap-on sonic flowmeter. The comparison of the <br />orifice with the flowmeter showed less than a 2-percent difference in flow measurement indicating <br />no problem with measurement of flow entering the model. <br /> <br />Volumetric calibrations were also performed to compare to the orifice meter readings. A known <br />volume in the head box of the model was filled and timed to obtain a discharge. This calibration <br />was within 1 percent of the orifice meter. These calibrations were necessary since the flows being <br />modeled were very small - as low as 50 ft' /s (0.036 ft' /s model). Care was taken during model <br />construction to prevent leakage through the Union Avenue dam and at the downstream rock dam. <br />Checks after the model was built confirmed that very little leakage occurred. <br /> <br />Calibration of dam, radial gate, and intake. - The Union Avenue dam was calibrated for flow vs. <br />water surface elevation by taking point gauge readings of the water surface approximately 30 feet <br />upstream of the boatchute. A discharge rating curve of the Union Avenue dam and boatchule is <br />presented on figures 9A and 98. Two regression equations are presented on figure 9A, depending <br />on the elevation of the water surface. The breaks in the curve correspond to the configuration of <br />the boatchute in relation to the water surface elevation. Figure 9B shows an enlargement of the <br />lower portion of the discharge rating curve. <br /> <br />The Englewood sluice radial gate was also calibrated for flow vs. water surface. Water surface <br />readings were made at the boatchute centerline about 30 feet upstream of the Union Avenue dam <br /> <br />5 <br />