Browsing by Author "Kincaid, George P."

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    Gas Transfer at Gated Sill Structures In the Ohio River Valley
    (St. Anthony Falls Laboratory, 1999-02) Urban, Alicia L.; Gulliver, John S.; Miller, Kimberly F.; Kincaid, George P.
    The Ohio River Valley is one of the most heavily industrialized basins in the United States. As a result, the Ohio River, Monogahela, MusldngUln, Kanawha, and other tributaries often experience poor water quality. One measure of poor water quality is low dissolved oxygen concentrations during low flow periods. Most of the rivers in the Ohio River Valley have been transformed into navigable waterways through a series of locks and dams. The free flowing river is now a series of pools. Quiescent pools do not promote the transfer of oxygen into the water due to low turbulence levels. Fortunately, the hydraulic structures themselves may actually be a key componen~ in improving the water quality because of the high turbulence levels generated at these structures. The purpose of this study is to investigate the use of dam gates and hydropower installations for the addition of oxygen to the water. The amount of oxygen added to the water varies with the structural characteristics, gate opening, and hydraulic conditions. Analysis of the most recent data taken in 1998, along with data taleen in previous years, shows trends for oxygen transfer at gate sill structures. Gate tests indicate that a high tailwater submergence of the sill allows minimal oxygen transfer to occur until an unsubmerged hydraulic jUlUP forms. The transfer efficiency will increase until a maximUlU transfer is reached. Beyond this critical gate opening, the transfer efficiency will level out or may even decline. If the submergence on the sill is low, a hydraulic jUlnp can form at very low gate settings. In this case, the transfer efficiencies will increase to a maximUlU at the critical gate opening. After this gate setting is reached, the transfer efficiencies will level out or decline. Te:;ts were also perfonned on hydropower installations with the draft tube air vent opened. Analysis of all sites indicates that oxygen transfer is negligible due to insufficient suction head. The minimal retrofit scheme is not suitable for raising oxygen levels. A more detailed study of retrofit options is needed to raise oxygen levels through hydrotuI'bine venting, In conclusion, the gated sill structures show promise as a tool for improving water quality within the river system by raising oxygen levels, if operated under close-tooptimum hydraulic conditions for gate aeration.
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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.