Date of Award
Master of Science (MS)
Biological and Irrigation Engineering
Gary P. Merkley
Surface velocity coefficients were calculated at five locations in three different irrigation canals in Logan, Utah. First, the total flow' rate was measured using current meters and calculated cross-sectional flow area. Second , the surface velocity was measured using four trials of the float method , and the average float travel time was calculated for each location and measurement instance. The measurements were taken on different days for various water depths in the canals. Third, the surface and mean cross-sectional velocities were divided , yielding the surface velocity coefficient, for every measurement at each of the five locations. Several channel bed elevations were also measured near each location along a distance of 100 m or more, as necessary, to define the average longitudinal bed slope. Linear equations and averages were developed from the relationship between the velocity ratios and critical depth, and between those ratios and the measured water depths. Finally, the approximate cross-sectional velocity profiles for several of the measurement instances were produced using GIS software.
All the steps mentioned above were followed to determine surface velocity coefficients for use with the float method. The results in the five locations show that the coefficients are not proportional to the water depth variation, and that the presence of rocks and sediment in the channel bed affect the coefficient values. Consequently, the development of a linear relation among coefficients to correct the surface velocity obtained from float method was difficult to obtain from the available data. In the five measurement locations, the surface velocity coefficients vary from 0.33 to 0.81 and the measured water depths during the period of evaluation were from 0.16 m to 0.53 m. No clear relationship was found between average water depth and surface velocity coefficient.
Escurra, Jorge, "Field Calibration of the Float Method in Open Channels" (2004). All Graduate Plan B and other Reports. Paper 352.
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