Browsing by Author "Hibbs, David E."

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    Gas Transfer Measurements at Hydraulic Structures on the Ohio River
    (St. Anthony Falls Laboratory, 1998-06) Hettiarachchi, Suresh L.; Gulliver, John S.; Hibbs, David E.; Howe, John; Miller, Kimberly F.; Kincaid, George P.
    Gas transfer at hydraulic structures has been a topic of interest for many years. Navigation dams on rivers can add a large amount of atmospheric gases to the water due to the high velocities and the turbulence generated as the water passes through these structures. The increase in air-water gas transfer is due to air entrainment and the formation of bubbles in the flow. Hence, gas transfer at hydraulic structures plays an important role in the water quality of a river-reservoir system. Measurement of air-water gas transfer at hydraulic structures is a complicated process. Oxygen has, historically, been the measured gas, but concentration levels close to saturation and significant vertical stratification in oxygen concentration in the upstream pool often hinder accurate transfer measurements. The U.S. Army Corps of Engineers, The u.s. Geological Survey, and th~ University of Minnesota have been involved in this project to measure gas transfer at hydraulic structures in the Ohio River basin, using in~ situ methane as a tracer in addition to measuring dissolved oxygen. The use of the two volatile chemicals increases the possibility of worthwhile field measurements. This project is conducted in order to evaluate gas transfer characteristics at various hydraulic structures on the Ohio River so that spills through the gates can be optimized. The hydropower producers on the Ohio River may also benefit from this information, as wastage of water from the reservoir to meet water quality requirements will be minimized. The results show that gas transfer increases significantly when a hydraulic jump forms in the stilling basin at gated sill structures, which is the type most commonly seen on the Ohio River. It is also clear that gas transfer at hydraulic structures is significantly affected by the structural characteristics and the hydraulic action at each site.
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    Hydraulic Model Study of the Siphon Intake to the Brasfield Dam Hydroelectric Facility
    (1992-04) Hibbs, David E.; Gulliver, John S.; Erickson, Benjamin G.
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    Methane Sampling Technique and the Measurement of Plunge Pool Impact on Gas Transfer Rates at Low-Head Hydraulic Structures
    (St. Anthony Falls Hydraulic Laboratory, 1993-11) Hibbs, David E.; Gulliver, John S.; McDonald, John P.
    Hydraulic structures have a large impact on the amount of dissolved gases in a river system. Even though the water passes over the structure for only a short time, the water flowing over a spillway or weir entrains air bubbles, creating significantly more air-water surface area for gas transfer. In addition, the high turbulence that occurs at most hydraulic structures will increase the transfer rate coefficients. The same quantity of gas transfer that normally would occur in several miles in a river can occur at a hydraulic structure. The transfer of oxygen from the atmosphere to the water is often of interest, therefore it seems logical to directly measure oxygen transfer. However, there are some problems associated with the measurement of dissolved oxygen (DO) concentration. If the DO level is close to saturation (within approximately 2.5 mg/.e) , the tremendous uncertainty associated with the current measurement techniques makes the estimation of gas transfer useless (Gulliver and Wilhelms, 1992). Also, if the reservoir is stratified, it is difficult to predict withdrawal from the various layers with the required precision, and usually impossible to sample at the spillway crest (Gulliver and Rindels, 1993). Because the required field conditions for accurate DO measurement often do not occur, other measurement techniques, such as the tracer technique are used.
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    Methane Sampling Technique and the Measurement of Plunge Pool Impact on Gas Transfer Rates at Low-Head Hydraulic Structures
    (St. Anthony Falls Laboratory, 1995-09) Hibbs, David E.; Gulliver, John S.; McDonald, John P.
    Hydraulic structures have a large impact on the amount of dissolved gases in a river system. Even though the water passes over the structure for only a short time, the water flowing over a spillway or weir entrains air bubbles, creating significantly more air-water surface area for gas transfer. In addition, the high turbulence that occurs at most hydraulic structures will increase the transfer rate coefficients. The same quantity of gas transfer that normally would occur in several miles in a river can occur at a hydraulic structure. The transfer of oxygen from the atmosphere to the water is often of interest; therefore, it seems logical to directly measure oxygen transfer. However, there are some problems associated with the measurement of dissolved oxygen (DO) concentration. If the DO level is close to saturation (within approximately 2.5 mg/l), the tremendous uncertainty associated with the current measurement techniques makes the estimation of gas transfer useless (Gulliver and Wilhelms 1992). Also, if the reservoir is stratified, it is difficult to predict withdrawal from the various layers with the required precision, and usually impossible to sample at the spillway crest (Gulliver and Rindels 1993). Because the required field conditions for accurate DO measurement often do not occur, other measurement techniques, such as the tracer technique, are used.