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Browsing by Author "Gates, TImothy K., advisor"

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    Experimental investigations for improving the accuracy of flow measurement in irrigation canals
    (Colorado State University. Libraries, 2021) Pugh, Joseph E., author; Venayagamoorthy, S. Karan, advisor; Gates, TImothy K., advisor; Windom, Bret C., committee member
    Flow measurement in open-channels refers to the process by which a volume amount of water passing through a channel cross section is quantified per unit time. In the irrigation water management context, this is done to account for available water resources so that water distribution systems can be properly managed to achieve adequate and efficient allocation. Today, irrigation water use remains the largest consumptive draw on our collective water budget, while the availability of this resource is becoming increasingly scarce. Additionally, access to reliable irrigation water acts as a major factor in maintaining strong crop production and healthy rural livelihoods. Improvement in the accuracy of flow measurement methodologies is then motivated by a need for implementing more conservative practices to limit unnecessary waste and to promote effective and equitable allocation. The two principal means by which flow is quantified in open-channels are the velocity-area method and the use of stage-discharge relationships associated with hydraulic structures placed within the channels. The present study investigates improvements to the accuracy of flow measurement for each of these methodologies. The velocity-area method involves the integration of several point measurements of velocity multiplied by sub-components of the channel cross-sectional area to achieve an estimate of flow rate via the principle of continuity. Traditionally, these methods have been time-consuming and subject to inaccuracy due to the large number of measurements needed. In recent decades, the development of Acoustic Doppler Current Profilers (ADCPs) has offered a means for measuring flow using the velocity-area method with time-efficiency and less intrusiveness into the flow. However, opportunity still exists for refining the operational protocols for this device to quantify and reduce measurement uncertainty, especially within the irrigation water management context. With this motivation, a StreamPro ADCP manufactured by Teledyne RD Instruments was used to quantify flow rates in man-made irrigation canals with the aim of determining best practices for: the method of deployment of an ADCP using a moving boat, the duration of the measurement transect per unit width of canal, and the number of transects to use in computing mean steady discharge. The purpose of these refinements is to better resolve a mean representation of the fluctuating turbulent velocity flow field by lessening user-induced uncertainty and estimating the point of diminishing returns for additional data collection. Suggested protocols developed from this experimentation indicate that a reduction of 30 to 70% in the values of uncertainty metrics can be accomplished utilizing a remotely operated tagline deployment method with a minimum transect duration relative to the canal top width of 24 s/m (7.3 s/ft), equivalent to 24 vertical pings per meter of an ADCP measuring at 1 Hz; and at least six total transects taken in reciprocal directions included in measurements of mean steady discharge. These findings provide further specificity beyond current guidelines to enhance the likelihood of practical implementation by ADCP users. Refinement of ADCP measurement protocols also serve as a chief aid in the accuracy of hydraulic structure calibration. As permanent fixtures within an open-channel, these structures rep- resent a means of obtaining continuous flow measurement without the time cost of velocity-area methods. The fundamental principle upon which hydraulic structures operate is the stage-discharge relationship. This equation relates an upstream measurement of the water surface elevation to the flow rate passing through the channel. However, the theoretical derivation of stage-discharge equations require several simplifying assumptions that must be corrected for using empirical calibration. In the present study, the nature of the stage-discharge relationship for a particular hydraulic structure known as the Obermeyer pivot weir is investigated. This device was primarily designed as a control for upstream water levels, and the current effort to establish a means by which the weir can be used for flow measurement purposes represents a novel contribution to the literature. In general, research on pivot weirs remains sparse, and no consensus has been reached concerning the correct theoretical approach for establishing the stage-discharge equation for this type of structure. Here, using a set of field observations, four alternative approaches are investigated to elucidate the optimal method for the use of pivot weirs for flow measurement. Specifically, a hypothesis concerning the effect of the changing angle of a pivot weir on the flow dynamics is tested. A recommended approach is given and informed by knowledge of practical implementation limitations. Finally, preliminary investigations using a laboratory model of the Obermeyer pivot weir are discussed, which offer insight into the complex nature of the dynamics for flow over this type of structure. The results of the present study offer important refinements to the current body of knowledge found within the literature and identify promising avenues for future research.