M. Leon Hyatt

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The discharge occurring in an open channel can be measured by placing a constriction in the channel. Flumes are commonly used as constriction in open channels. A flume is a specially designed and calibrated section built into a channel, the physical properties of which allow the calculation of the discharge. The narrowest section of the flume is usually called the throat. The velocity of flow through the throat, for any given flow rate, increases with a decrease in the flow depth. The ideal condition for measurement of discharge is a throat sufficiently constricted to produce critical-depth in the throat. Whenever the geometry of a channel produces critical flow the relationship between discharge and head is independent of conditions downstream, making discharge a function of only the upstream depth. Thus, when critical-depth occurs in the throat, the only measurement required to determine the discharge through the flume is the upstream depth of flow, thus making the wide use of critical-depth flumes desirable for measurement purposes. Flumes of carious shapes are used to obtain a condition of critical-depth, the most common and well known being the Parshall flume.

One purpose of this investigation has been to study the trapezoidal shaped flumes which several researches (Ackers and Harrison, 1963; Ludwig and Ludwig, 1951; Palmer and Bowlus, 1936; Robinson and Chamberlain, 1962; and Wells and Gotaas, 1948) have investigated. However, the primary purpose of this investigation has been the design, calibration, and evaluation, by model study, of a trapezoidal measuring flume to be constructed in the distribution system of the D.M.A.D. Company (Delta, Melville, Abraham, and Deseret Irrigation Companies) in Delta, utah. The flume to be constrcuted will be used to measure irrigation waters in a canal (Canal "B") having a capacity of 300 cfs (cubic feet per second) and located below the D.M.A.D. Dam.

The essential objectives of the model study have been: (1) investigation of several entrance and exit conditions to obtain the most economical, efficient, and practical design, (2) correlation of the data from this study with that of previous research, and (3) comparison of head losses in trapezoidal flumes with those of rectangular and Parshall flumes.

The trapezoidal flume has been designed as a critical-depth flume utilizing present tailwater conditions (the present depth-discharge relationship for Canal "B" is illustrated in Figure 1). However, increased developments by the D.M.A.D. Company in the channel downstream from the proposed flume may yield increased depth of flow for any particular discharge, thereby increasing the degree of submergence. In case the tailwater depths should rise much above the present levels for any particular discharge, submergence of the flume will undoubtedly occur and then two variables will have to be measured both the upstream and tailwater depths. Consequently, the calibration of the trapezoidal measuring flume was extended to submerged flow in this investigation.

After the prototype structure has been constructed, a field calibration will be conducted. This field calibration will be compared with the calibration for the prototype structure as predicted from the model study. Neither the field calibration nor the comparison between the field and model prediction calibrations will be incorporated into this thesis.